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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549





FORM 10-Q







|x | QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ---------------------------------------------------------------------------------------

For the quarterly period ended June 30, 2008

OR



| ̈ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------

For the transition period from  to

Commission File Number 000-33095





ACHILLION PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its
charter)







|                                                               |  |                                     
|-------------------------------------------------------------- |  | ------------------------------------
|Delaware                                                       |  | 52-2113479                          
|(State or other jurisdiction of incorporation or organization) |  | (I.R.S. Employer Identification No.)
|                                                               | 
|300 George Street, New Haven, CT                               |  | 06511                               
|(Address of principal executive offices)                       |  | (Zip Code)                          

(203) 624-7000

(Registrants telephone number, including area code)





Indicate by check mark whether
the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports),
and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No   ̈

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, non-accelerated filer or a smaller reporting company.
See definition of accelerated filer, large accelerated filer and smaller reporting company in Rule 12b-2 of the Exchange Act. (Check one):



|                                            |  |   |  |                           |  |  
|------------------------------------------- |  | - |  | ------------------------- |  | -
|Large accelerated filer                     |  |  ̈ |  | Accelerated filer         |  |  ̈
|                                            |  |   | 
|Non-accelerated filer                       |  |  ̈ |  | Smaller reporting company |  | x
|                                           
|(Do not check if smaller reporting company)

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the
Exchange Act).    Yes   ̈    No  x

As of August 13, 2008, the registrant had 26,376,078 shares of Common Stock, $0.001 par value per share, outstanding.









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INDEX



|                                                                                                         |  |           
|-------------------------------------------------------------------------------------------------------- |  | ----------
|                                                                                                         |  | PAGENUMBER
|PART I. FINANCIAL INFORMATION                                                                            |  |           
|                                                                                                         | 
|ITEM 1. FINANCIAL STATEMENTS                                                                             |  |           
|Condensed Balance Sheets at June 30, 2008 and December 31, 2007 (unaudited)                              |  | 3         
|Condensed Statements of Operations for the Three and Six Months Ended June 30, 2008 and 2007 (unaudited) |  | 4         
|Condensed Statements of Cash Flows for the Six Months Ended June 30, 2008 and 2007 (unaudited)           |  | 5         
|Notes to Financial Statements                                                                            |  | 6         
|                                                                                                         | 
|ITEM 2. MANAGEMENTS DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS            |  | 14        
|                                                                                                         | 
|ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK                                       |  | 24        
|                                                                                                         | 
|ITEM 4. CONTROLS AND PROCEDURES                                                                          |  | 24        
|                                                                                                         | 
|PART II. OTHER INFORMATION                                                                               |  |           
|                                                                                                         | 
|ITEM 1A. RISK FACTORS                                                                                    |  | 24        
|                                                                                                         | 
|ITEM 4. SUBMISSION OF MATTER TO A VOTE OF SECURITY HOLDERS                                               |  | 40        
|                                                                                                         | 
|ITEM 6. EXHIBITS                                                                                         |  | 40        



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PART I. FINANCIAL INFORMATION



|ITEM 1. | FINANCIAL STATEMENTS
|------- | --------------------

Achillion Pharmaceuticals, Inc.

Balance Sheets

(in thousands, except per share amounts)

(Unaudited)



|                                                                                                                        |  |               |          |   |                   |   |          |  
|----------------------------------------------------------------------------------------------------------------------- |  | ------------- | -------- | - | ----------------- | - | -------- | -
|                                                                                                                        |  | June 30, 2008 |          |   | December 31, 2007 |  
|Assets                                                                                                                  |  |               |          |   |                   |   |          |  
|Current assets:                                                                                                         |  |               |          |   |                   |   |          |  
|Cash and cash equivalents                                                                                               |  | $             | 10,758   |   |                   | $ | 8,971    |  
|Marketable securities                                                                                                   |  |               | 11,224   |   |                   |   | 22,138   |  
|Accounts receivable                                                                                                     |  |               | 369      |   |                   |   | 136      |  
|Prepaid expenses and other current assets                                                                               |  |               | 566      |   |                   |   | 1,671    |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total current assets                                                                                                    |  |               | 22,917   |   |                   |   | 32,916   |  
|Fixed assets, net                                                                                                       |  |               | 2,089    |   |                   |   | 2,475    |  
|Deferred financing costs                                                                                                |  |               | 115      |   |                   |   | 36       |  
|Restricted cash                                                                                                         |  |               | 205      |   |                   |   | 205      |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total assets                                                                                                            |  | $             | 25,326   |   |                   | $ | 35,632   |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Liabilities and Stockholders Equity                                                                                    |  |               |          |   |                   |   |          |  
|Current liabilities:                                                                                                    |  |               |          |   |                   |   |          |  
|Accounts payable                                                                                                        |  | $             | 1,665    |   |                   | $ | 2,083    |  
|Accrued expenses                                                                                                        |  |               | 2,766    |   |                   |   | 2,748    |  
|Deferred revenue                                                                                                        |  |               | 1,290    |   |                   |   | 1,298    |  
|Current portion of long-term debt                                                                                       |  |               | 9,062    |   |                   |   | 6,563    |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total current liabilities                                                                                               |  |               | 14,783   |   |                   |   | 12,692   |  
|Accrued expenses, net of current portion                                                                                |  |               | 114      |   |                   |   | 130      |  
|Deferred revenue                                                                                                        |  |               | 424      |   |                   |   | 1,272    |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total liabilities                                                                                                       |  |               | 15,321   |   |                   |   | 14,094   |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Commitments                                                                                                             |  |               |          |   |                   |   |          |  
|Stockholders Equity:                                                                                                   |  |               |          |   |                   |   |          |  
|Common Stock, $.001 par value; 100,000 shares authorized: 15,659 and 15,637 shares issued and outstanding, respectively |  |               | 16       |   |                   |   | 16       |  
|Additional paid-in capital                                                                                              |  |               | 174,601  |   |                   |   | 173,301  |  
|Accumulated deficit                                                                                                     |  |               | (164,616 | ) |                   |   | (151,830 | )
|Accumulated other comprehensive income                                                                                  |  |               | 4        |   |                   |   | 51       |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total stockholders equity                                                                                              |  |               | 10,005   |   |                   |   | 21,538   |  
|                                                                                                                        |  |               |          |   |                   |   |          |  
|Total liabilities and stockholders equity                                                                              |  | $             | 25,326   |   |                   | $ | 35,632   |  
|                                                                                                                        |  |               |          |   |                   |   |          |  

The accompanying notes are an integral part of these financial statements.



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Achillion Pharmaceuticals, Inc.

Statements of Operations

(in
thousands, except per share amounts)

(Unaudited)



|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|------------------------------------------------------------------------------ |  | ----------------------------------- | ------ | - | --------------------------------- | - | ------ | ---- |  | - | ------- | - |  | - | ------- | -
|                                                                               |  | For the Three Months Ended June 30, |        |   | For the Six Months Ended June 30, |  
|                                                                               |  | 2008                                |        |   | 2007                              |   |        | 2008 |  |   | 2007    |  
|Revenue                                                                        |  | $                                   | 398    |   |                                   | $ | 1,195  |      |  | $ | 1,025   |   |  | $ | 2,745   |  
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Operating expenses                                                             |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Research and development                                                       |  |                                     | 5,483  |   |                                   |   | 7,719  |      |  |   | 10,481  |   |  |   | 16,085  |  
|General and administrative                                                     |  |                                     | 1,608  |   |                                   |   | 1,723  |      |  |   | 3,296   |   |  |   | 3,271   |  
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Total operating expenses                                                       |  |                                     | 7,091  |   |                                   |   | 9,442  |      |  |   | 13,777  |   |  |   | 19,356  |  
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Loss from operations                                                           |  |                                     | (6,693 | ) |                                   |   | (8,247 | )    |  |   | (12,752 | ) |  |   | (16,611 | )
|Other income (expense)                                                         |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Interest income                                                                |  |                                     | 162    |   |                                   |   | 666    |      |  |   | 453     |   |  |   | 1,424   |  
|Interest expense                                                               |  |                                     | (308   | ) |                                   |   | (242   | )    |  |   | (559    | ) |  |   | (506    | )
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Net loss before tax benefits                                                   |  |                                     | (6,839 | ) |                                   |   | (7,823 | )    |  |   | (12,858 | ) |  |   | (15,693 | )
|Tax benefit                                                                    |  |                                     | 50     |   |                                   |   | 170    |      |  |   | 72      |   |  |   | 371     |  
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Net loss                                                                       |  |                                     | (6,789 | ) |                                   |   | (7,653 | )    |  |   | (12,786 | ) |  |   | (15,322 | )
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Basic and diluted net loss per share (Note 3)                                  |  | $                                   | (0.43  | ) |                                   | $ | (0.49  | )    |  | $ | (0.82   | ) |  | $ | (0.99   | )
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Weighted average shares used in computing basic and diluted net loss per share |  |                                     | 15,646 |   |                                   |   | 15,556 |      |  |   | 15,642  |   |  |   | 15,548  |  
|                                                                               |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  

The accompanying notes are an integral part of these financial statements.



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Achillion Pharmaceuticals, Inc.

Statements of Cash Flows

(in
thousands)

(Unaudited)



|                                                                            |  |                           |         |   |      |   |         |  
|--------------------------------------------------------------------------- |  | ------------------------- | ------- | - | ---- | - | ------- | -
|                                                                            |  | Six Months Ended June 30, |        
|                                                                            |  | 2008                      |         |   | 2007 |  
|Cash flows from operating activities                                        |  |                           |         |   |      |   |         |  
|Net loss                                                                    |  | $                         | (12,786 | ) |      | $ | (15,322 | )
|Adjustments to reconcile net loss to net cash used in operating activities: |  |                           |         |   |      |   |         |  
|Depreciation and amortization                                               |  |                           | 419     |   |      |   | 372     |  
|Noncash stock-based compensation                                            |  |                           | 1,092   |   |      |   | 811     |  
|Noncash interest expense                                                    |  |                           | 75      |   |      |   | 58      |  
|Loss on disposal of equipment                                               |  |                           |        |   |      |   | 2       |  
|Amortization of discount on securities                                      |  |                           | (284    | ) |      |   | (1,036  | )
|Changes in operating assets and liabilities:                                |  |                           |         |   |      |   |         |  
|Accounts receivable                                                         |  |                           | (233    | ) |      |   | 766     |  
|Prepaid expenses and other current assets                                   |  |                           | 1,105   |   |      |   | 161     |  
|Account payable                                                             |  |                           | (418    | ) |      |   | 600     |  
|Accrued expenses                                                            |  |                           | 2       |   |      |   | 1,287   |  
|Deferred revenue                                                            |  |                           | (856    | ) |      |   | (1,690  | )
|                                                                            |  |                           |         |   |      |   |         |  
|Net cash used in operating activities                                       |  |                           | (11,884 | ) |      |   | (13,991 | )
|                                                                            |  |                           |         |   |      |   |         |  
|Cash flows from investing activities                                        |  |                           |         |   |      |   |         |  
|Purchase of property and equipment                                          |  |                           | (12     | ) |      |   | (418    | )
|Purchase of available for sale marketable securities                        |  |                           | (11,613 | ) |      |   | (38,428 | )
|Maturities of marketable securities                                         |  |                           | 22,764  |   |      |   | 40,430  |  
|                                                                            |  |                           |         |   |      |   |         |  
|Net cash provided by investing activities                                   |  |                           | 11,139  |   |      |   | 1,584   |  
|                                                                            |  |                           |         |   |      |   |         |  
|Cash flows from financing activities                                        |  |                           |         |   |      |   |         |  
|Proceeds from exercise of stock options                                     |  |                           | 13      |   |      |   | 65      |  
|Proceeds from sale of common stock under the Employee Stock Purchase Plan   |  |                           | 40      |   |      |   | 93      |  
|Proceeds from repayment of stock subscription receivable                    |  |                           |        |   |      |   | 49      |  
|Borrowings under notes payable                                              |  |                           | 5,000   |   |      |   | 800     |  
|Repayments of notes payable                                                 |  |                           | (2,421  | ) |      |   | (1,759  | )
|Payment of deferred financing costs                                         |  |                           | (100    | ) |      |   |        |  
|                                                                            |  |                           |         |   |      |   |         |  
|Net cash provided by (used in) financing activities                         |  |                           | 2,532   |   |      |   | (752    | )
|                                                                            |  |                           |         |   |      |   |         |  
|Net increase (decrease) in cash and cash equivalents                        |  |                           | 1,787   |   |      |   | (13,159 | )
|Cash and cash equivalents, beginning of period                              |  |                           | 8,971   |   |      |   | 22,662  |  
|                                                                            |  |                           |         |   |      |   |         |  
|Cash and cash equivalents, end of period                                    |  | $                         | 10,758  |   |      | $ | 9,503   |  
|                                                                            |  |                           |         |   |      |   |         |  
|Supplemental disclosure of cash flow information                            |  |                           |         |   |      |   |         |  
|Cash paid for interest                                                      |  | $                         | 442     |   |      | $ | 453     |  
|Cash received from tax credits                                              |  | $                         | 1,008   |   |      | $ |        |  
|Supplemental disclosure of noncash financing activities                     |  |                           |         |   |      |   |         |  
|Issuance of warrants in connection with debt financing                      |  | $                         | 155     |   |      | $ |        |  
|Cashless exercise of warrants                                               |  | $                         |        |   |      | $ | 282     |  

The accompanying notes are an integral part of these financial statements.



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Achillion Pharmaceuticals, Inc.

Notes to Financial Statements

(in
thousands, except per share amounts)

1. Nature of the Business

Achillion Pharmaceuticals, Inc. (the Company) was incorporated on August 17, 1998 in Delaware. The Company was established to discover, develop and commercialize innovative anti-infective drug
therapies. The Company is devoting substantially all of its efforts towards product research and development.

The Company has incurred
losses of $150,753 from inception through June 30, 2008 and had an accumulated deficit of $164,616 through June 30, 2008. The Company has funded its operations primarily through the sale of equity securities, borrowings from debt
facilities, and the receipt of license fees, milestone and cost-sharing receipts from its collaboration partner, Gilead Sciences, Inc. (Gilead).

The Company expects to incur substantial and increasing losses for at least the next several years and will need substantial additional financing to obtain regulatory approvals, fund operating losses, and, if deemed
appropriate, establish manufacturing and sales and marketing capabilities, which the Company will seek to raise through public or private equity or debt financings, collaborative or other arrangements with third parties or through other sources of
financing. There can be no assurance that such funds will be available on terms favorable to the Company, if at all.

In addition to the
normal risks associated with early-stage companies, there can be no assurance that the Company will successfully complete its research and development, obtain adequate patent protection for its technology, obtain necessary government regulatory
approval for drug candidates the Company develops or that any approved drug candidates will be commercially viable. In addition, the Company may not be profitable even if it succeeds in commercializing any of its drug candidates.

2. Basis of Presentation

The accompanying unaudited
condensed financial statements of the Company should be read in conjunction with the audited financial statements and notes as of and for the year ended December 31, 2007 included in the Companys Annual Report on Form 10-K filed with the
SEC on March 5, 2008. The accompanying financial statements have been prepared in accordance with generally accepted accounting principles in the United States (U.S. GAAP) for interim financial information, in accordance with the
instructions to Form 10-Q and the guidance in Article 10 of Regulation S-X. Accordingly, since they are interim financial statements, the accompanying financial statements do not include all of the information and disclosures required by
U.S. GAAP for complete financial statements. The accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, that are, in the opinion of management, necessary for a fair statement of the results of
operations for the interim periods presented. Interim results are not necessarily indicative of results for a full year.

The preparation
of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements and notes thereto. A discussion of the Companys critical accounting policies
and management estimates is described in Managements Discussion and Analysis of Financial Condition and Results of Operations included in Part I, Item II of this quarterly report on Form 10-Q.

3. Earnings (Loss) Per Share (EPS)

Basic
EPS is calculated in accordance with Statement of Financial Accounting Standards (SFAS) No. 128, Earnings per Share, or SFAS No. 128, by dividing net income or loss attributable to common stockholders by the weighted
average common stock outstanding. Diluted EPS is calculated in accordance with SFAS No. 128 by adjusting weighted average common shares outstanding for the dilutive effect of common stock options and warrants. In periods in which a net loss is
recorded, no effect is given to potentially dilutive securities, since the effect would be antidilutive. Total securities that could potentially dilute basic EPS in the future were not included in the computation of diluted EPS because to do so
would have been antidilutive for the three and six months ended June 30, 2008 and 2007. Basic EPS for the three and six months ended June 30, 2008 and 2007 were as follows (prior to consideration of the treasury stock method):



|                                                  |  |                                     |  |      
|------------------------------------------------- |  | ----------------------------------- |  | -----
|                                                  |  | Three and Six Months Ended June 30,
|                                                  |  | 2008                                |  | 2007 
|Options                                           |  | 1,834                               |  | 1,182
|Warrants                                          |  | 354                                 |  | 312  
|                                                  |  |                                     |  |      
|Total potentially dilutive securities outstanding |  | 2,188                               |  | 1,494
|                                                  |  |                                     |  |      



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4. Collaboration Arrangement

In November 2004, the Company entered into a collaboration arrangement with Gilead Sciences Inc. (the Gilead Arrangement) to jointly develop and commercialize compounds for use in treating hepatitis C
infection which inhibit viral replication through a specified novel mechanism of action. Commercialization efforts will commence only if such compounds are found to be commercially viable and all appropriate regulatory approvals have been obtained.
In connection with this arrangement, Gilead paid the Company $10,000 as payment for both a non-refundable upfront license fee and 2,300 shares of Series C-1 Convertible Preferred Stock (Series C-1).

Under the Gilead Arrangement, the Company and Gilead are working together to develop one or more compounds for use in treating hepatitis C infection
until proof-of-concept in one compound, as defined in the Gilead Arrangement, is achieved (the Research Period). Subsequent to the achievement of proof-of-concept, the Company has no further obligation to continue providing services to
Gilead but, at Gileads request, the Company may elect to extend the Research Period for up to an additional two years after proof-of-concept is established, based upon good faith negotiations at that point in time. Further, if it is agreed
that potential back-up compounds should continue to be researched, good faith negotiations would also be conducted to determine the specifics of any arrangement to continue to research backup compounds.

Gilead has agreed to make milestone payments to the Company upon the achievement of various defined clinical, regulatory and commercial milestones, such
as regulatory approval in the United States, the European Union, or Japan. The Company could receive up to $157,500 in development, regulatory and sales milestone payments, assuming the successful simultaneous development of a lead and back-up
compound, and annual sales in excess of $600,000. The Company could also receive royalties on net sales of products if commercialization is achieved.

The up-front payment of $10,000, received in 2004, was first allocated to the fair value of the Series C-1, as determined by management after considering a valuation analysis performed by an unrelated third-party
valuation firm, Fletcher Spaght, at the direction of the Company, in which each share of the Series C-1 was determined to be worth $0.88 per share, or approximately $2,000 in aggregate. The remaining $8,000 balance of the $10,000 is being accounted
for as a non-refundable up-front license fee. Due to certain provisions contained within the Gilead Arrangement relating to services to be performed on both the primary and backup compounds, as defined in the Gilead Arrangement, the non-refundable
up-front license fee of $8,000, as well as a $2,000 milestone achieved during the Research Period, is being accounted for under the proportionate performance model. Future milestones, if any, will occur after the Research Period and are not
accounted for under the proportionate performance model. Revenue recognized under the proportionate performance model is limited by the aggregate cash received or receivable to date by the Company. Milestones achieved, if any, after the termination
of the Research Period, will be recognized when the milestone is achieved as the Company has no further research or development obligations after the Research Period.

Under the Gilead Arrangement, through March 31, 2007, agreed upon research or development expenses, including internal full-time equivalent (FTE) costs and external costs, incurred by both companies
during the period up to proof-of-concept were borne equally by both parties. Prior to March 31, 2007, the Company was incurring the majority of those expenses and, therefore, was the net receiver of funds under this cost-sharing portion of the
arrangement. Effective April 1, 2007, internal full-time equivalent costs are no longer subject to this cost-sharing arrangement. Instead, each party bears its own internal costs, including FTE costs. External costs continue to be shared
equally by both parties. In March 2007, the Company and Gilead also revised their joint research program to focus on next-generation NS4A antagonists, after discontinuing clinical trials for ACH-806, an NS4A antagonist the Company was previously
evaluating. Pursuant to the project plan under the Gilead Arrangement, the Companys remaining obligations under the plan continue through the third quarter of 2009.



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Gilead has the right to terminate the agreement without cause upon 120 days written notice to the
Company. Upon termination of the Gilead Arrangement for any reason, all cost share amounts due and payable through the date of termination shall be paid by the appropriate party and no previously paid amounts will be refundable.

During the three months ended June 30, 2008 and 2007, the Company recognized revenue of $398 and $1,195, under the Gilead Arrangement, respectively,
of which $251 and $722, respectively, related to the recognition of the non-refundable upfront fee and a pre-proof-of-concept milestone under the proportionate performance model. The remaining $147 and $473 recognized during the three months ended
June 30, 2008 and 2007, relate to FTE reimbursements recognized under the proportionate performance model and external costs billed under the Gilead Arrangement, net of the receipt of payments from Gilead of $2 for the three months ended
June 30, 2008 and net of payments to Gilead of $109 for the three months ended June 30, 2008 and 2007, respectively. Payments to Gilead under this collaboration are recognized as a reduction in revenue.

During the six months ended June 30, 2008 and 2007, the Company recognized revenue of $1,025 and $2,710, under the Gilead Arrangement, respectively,
of which $533 and $1,475, respectively, related to the recognition of the non-refundable upfront fee and a pre-proof-of-concept milestone under the proportionate performance model. The remaining $492 and $1,235 recognized during the six months ended
June 30, 2008 and 2007, relate to FTE reimbursements recognized under the proportionate performance model and external costs billed under the Gilead Arrangement, net of payments made to Gilead of $24 and $358 for the six months ended
June 30, 2008 and 2007, respectively. Payments to Gilead under this collaboration are recognized as a reduction in revenue.

Included
in the accompanying balance sheets as of June 30, 2008 and December 31, 2007 are $294 and $989 respectively, of accounts receivable resulting from this collaboration agreement and $1,714 and $2,570, respectively, of deferred revenue
resulting from the up-front fee, a milestone payment, and FTE costs. In addition to Gileads rights to unilaterally terminate this agreement, each party has the right to terminate for material breach; however, the Company may terminate for
Gileads breach only on a market-by-market basis, and, if applicable, a product-by-product basis.

5. Marketable Securities

The Company adopted SFAS No. 157, Fair Value Measurements,or SFAS No. 157, effective January 1, 2008 for financial assets and
liabilities measured on a recurring basis. There was no impact to the Companys financial statements upon the adoption of SFAS No. 157. SFAS No. 157 requires disclosure that establishes a framework for measuring fair value and expands
disclosures in the financial statements. The statement requires that fair value measurements be classified and disclosed in one of the three categories:

Level 1: Quoted prices in active markets for identical assets and liabilities that the reporting entity has the ability to access at the measurement date;

Level 2: Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; or

Level 3: Unobservable inputs.

The fair value of the Companys securities of $11,224 as of June 30, 2008 is valued based on level 2 inputs as defined in SFAS No. 157. The Company classifies its entire investment portfolio as available for sale as defined
in SFAS No. 115, Accounting for Certain Investments in Debt and Equity Securities. As of June 30, 2008 and December 31, 2007, the Companys investment portfolio consisted of U.S. government and agency securities and short
term commercial paper held by a major banking institution. The maturities of all marketable securities held at June 30, 2008 and December 31, 2007 are less than one year. Securities are carried at fair value with the unrealized gains
(losses) reported as a separate component of stockholders equity.

The unrealized gain from marketable securities was $4 and $51 at
June 30, 2008 and December 31, 2007, respectively.

As of June 30, 2008 and December 31, 2007, none of the
Companys investments were determined to be other than temporarily impaired.



8



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6. Accrued Expenses

Current and long-term accrued expenses consist of the following:



|                                          |  |               |       |                   |   |      
|----------------------------------------- |  | ------------- | ----- | ----------------- | - | -----
|                                          |  | June 30, 2008 |       | December 31, 2007
|Accrued compensation                      |  | $             | 953   |                   | $ | 720  
|Accrued research and development expenses |  |               | 1,417 |                   |   | 1,618
|Accrued professional fees                 |  |               | 244   |                   |   | 294  
|Other accrued expenses                    |  |               | 266   |                   |   | 246  
|                                          |  |               |       |                   |   |      
|Total                                     |  | $             | 2,880 |                   | $ | 2,878
|                                          |  |               |       |                   |   |      

Accrued research and development expenses are comprised of amounts owed to third-party contract
research organizations or CROs, clinical investigators, laboratories and data managers for research and development work performed on behalf of the Company.

7. Debt

Debt consists of the following:



|                                                                                                                                                                |  |               |        |   |                   |   |        |  
|--------------------------------------------------------------------------------------------------------------------------------------------------------------- |  | ------------- | ------ | - | ----------------- | - | ------ | -
|                                                                                                                                                                |  | June 30, 2008 |        |   | December 31, 2007 |  
|CII Term Loan, payable in monthly installments of $13 through September 2010 with a final balloon payment of $686, with interest at
7.5% per annum              |  | $             | 890    |   |                   | $ | 933    |  
|2003 Credit Facility, payable in monthly installments as the individual notes mature through December 2010, with interest ranging from 7.75%
to 9.06% per annum |  |               | 525    |   |                   |   | 675    |  
|2005 Credit Facility, payable in monthly installments as notes mature through December 2009, with interest of 10.92% to 11.58% per annum                        |  |               |       |   |                   |   | 4,955  |  
|2008 Credit Facility, payable in monthly installments as notes mature through March 2011, with interest of 9.97% to 11.58% per
annum                            |  |               | 7,647  |   |                   |   |       |  
|                                                                                                                                                                |  |               |        |   |                   |   |        |  
|Total long-term debt                                                                                                                                            |  |               | 9,062  |   |                   |   | 6,563  |  
|Less: current portion                                                                                                                                           |  |               | (9,062 | ) |                   |   | (6,563 | )
|                                                                                                                                                                |  |               |        |   |                   |   |        |  
|Total long-term debt, net of current portion                                                                                                                    |  | $             |       |   |                   | $ |       |  
|                                                                                                                                                                |  |               |        |   |                   |   |        |  

In February 2008, the Company entered into a credit facility with GE Capital Corporation and
Oxford Finance Corporation. This facility has substantially the same terms as the 2005 Credit Facility. At the same time, the Company combined the amounts outstanding under the 2005 Credit Facility with the newly issued notes (collectively, the
2008 Credit Facility). The 2008 Credit Facility provided $5,000 to fund the Companys working capital needs, and is collateralized by substantially all of the Companys tangible assets. In connection with the 2008 Credit
Facility, the Company issued warrants to purchase 43 shares of common stock at an exercise price of $4.68 per share. The fair value of the warrants at the date of issuance was estimated to be $155, utilizing the Black Scholes method and was recorded
as a debt discount. This amount is being amortized as interest expense over the term of the loan.

All of the Companys debt
agreements contain certain subjective acceleration clauses, such that upon the occurrence of a material adverse change in the financial condition, business or operations of the Company in the view of the lenders (Material Adverse
Change), amounts due under the agreement may become immediately due and payable. The Company has no indication that it is in default of any Material Adverse Change clauses, and none of the Companys lenders have accelerated scheduled loan
payments as a result of these provisions.

8. Stock-Based Compensation

The Companys 2006 Stock Incentive Plan, or the 2006 Plan, is administered by the Companys Board of Directors and provides for the grant of incentive stock options, nonstatutory stock options, restricted
stock, restricted stock units, stock appreciation rights and other stock-based awards. The Companys officers, employees, consultants, advisors and directors are eligible to receive awards under the 2006 Plan; however, incentive stock options
may only be granted to employees. Options granted are exercisable for a period determined by the Company, but in no event longer than ten years from the date of the grant. Options generally vest ratably over four years. There were 789 shares
available to be granted under the 2006 Plan as of June 30, 2008.



9



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##### Table of Contents

A summary of the status of the Companys stock option activity for the six months ended
June 30, 2008 is presented in the table and narrative below:



|                                                                 |  |         |   |  |                              |     
|---------------------------------------------------------------- |  | ------- | - |  | ---------------------------- | ----
|                                                                 |  | Options |   |  | WeightedAverageExercisePrice
|Outstanding at January 1, 2008                                   |  | 1,857   |   |  | $                            | 5.97
|Granted                                                          |  | 16      |   |  |                              | 4.41
|Exercised                                                        |  | (7      | ) |  |                              | 1.82
|Cancelled/Forfeited                                              |  | (32     | ) |  |                              | 6.78
|                                                                 |  |         |   |  |                              |     
|Outstanding at June 30, 2008                                     |  | 1,834   |   |  | $                            | 5.96
|                                                                 |  |         |   |  |                              |     
|Options exercisable at June 30, 2008                             |  | 925     |   |  | $                            | 4.69
|                                                                 |  |         |   |  |                              |     
|Weighted-average fair value of options granted during the period |  |         |   |  | $                            | 2.65

The Company utilizes the Black-Scholes option pricing model for determining the estimated fair
value for stock-based awards. The Black-Scholes model requires the use of assumptions which determine the fair value of the stock-based awards. The assumptions used to value options granted are as follows:



|                        |  |                          |   |  |               |  
|----------------------- |  | ------------------------ | - |  | ------------- | -
|                        |  | For the Six Months Ended |  
|                        |  | June 30, 2008            |   |  | June 30, 2007 |  
|Expected term of option |  | 6.1 years                |   |  | 6.1 years     |  
|Expected volatility     |  | 64                       | % |  | 70            | %
|Risk free interest rate |  | 2.67  3.48              | % |  | 4.51  4.94   | %
|Expected dividend yield |  | 0                        | % |  | 0             | %

Total compensation expense recorded in the accompanying statements of operations associated with
option grants made to employees for the three months ended June 30, 2008 and 2007 was $525 and $400, respectively. Total compensation expense recorded in the accompanying statements of operations associated with option grants made to employees
for the six months ended June 30, 2008 and 2007 was $1,058 and $807, respectively. The Company recorded no tax benefit related to these options since the Company currently maintains a full valuation allowance.

As of June 30, 2008, the intrinsic value of the options outstanding was $316, of which $300 related to vested options and $16 related to unvested
options. The intrinsic value of stock options is calculated based on the difference between the exercise prices of the underlying awards and the quoted stock price of the Companys common stock as of the reporting date.

As of June 30, 2008, the total compensation cost related to unvested options not yet recognized in the financial statements is approximately $4,276,
net of estimated forfeitures, and the weighted average period over which this amount is expected to be recognized is 1.44 years.

The
Company also occasionally grants stock option awards to consultants. Such grants are accounted for pursuant to Emerging Issue Task Force (EITF) No. 96-18, Accounting for Equity Instruments That Are Issued to Other Than Employees
for Acquiring, or in Conjunction with Selling, Goods or Services.Accordingly, the Company recognizes compensation expense equal to the fair value of such awards and amortizes such expense over the performance period. Total expense for the three
months ended June 30, 2008 and 2007 was $4 and $1, respectively and total expense for the six months ended June 30, 2008 and 2007 was $13 and $4, respectively.

9. Income Taxes

The Company uses an asset and liability approach for financial accounting and
reporting of income taxes. Deferred tax assets and liabilities are determined based on temporary differences between financial reporting and tax basis of assets



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##### Table of Contents

and liabilities and are measured by applying enacted rates and laws to taxable years in which differences are expected to be recovered or settled. Further,
the effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that the rate changes.

Effective January 1, 2007, the Company adopted Financial Accounting Standards Board, (FASB) Interpretation No. 48, Accounting for Uncertainty in Income Taxesan interpretation of FASB Statement No. 109,or FIN 48. FIN 48 prescribes a comprehensive model for how a company should recognize, measure, present, and disclose in its financial statements uncertain tax positions that the company has taken or expects to take on a tax return
(including a decision whether to file or not file a return in a particular jurisdiction). Under FIN 48, the financial statements reflect expected future tax consequences of such positions presuming the taxing authorities full knowledge of the
position and all relevant facts.

The federal and state tax authorities could challenge tax positions taken by the Company for the periods
for which there are open tax years. Years subject to audit are years in which unused net operating losses were generated that remain open by the statute of limitations. The Company is open to challenge for the periods of 1998 through 2007 in federal
and the State of Connecticut jurisdictions.

The Company did not have any unrecognized tax benefits as of the date of adoption of FIN 48 or
June 30, 2008.

At December 31, 2007, the Companys federal and state net operating loss carryforwards, or NOLs, were
approximately $130,186 and $131,774, respectively, and the Company had gross deferred income tax assets of approximately $62,044, which resulted primarily from the federal and state NOL and tax credit carryforwards. In accordance with SFAS
No. 109, Accounting for Income Taxes, the Company maintains a full valuation allowance against its deferred tax assets and liabilities.

Utilization of the NOL and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, or Section 382, due to changes in ownership of the
Company that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax. In
general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period. Since
the Companys formation, the Company has raised capital through the issuance of capital stock on several occasions which, combined with the purchasing shareholders subsequent disposition of those shares, may have resulted in a change of
control, as defined by Section 382. Due to the significant complexity and cost associated with a change in control study, and because there could be additional changes in control in the future, the Company has not assessed whether there has
been one or more changes in control since the Companys formation. If the Company has experienced a change of control at any time since Company formation, utilization of its NOL or research and development credit carryforwards would be subject
to an annual limitation under Section 382. Any limitation may result in expiration of a portion of the NOL or research and development credit carryforwards before utilization which would reduce the Companys gross deferred tax assets.

The Company does not have any interest or penalties accrued related to tax positions as it does not have any unrecognized tax benefits. In
the event the Company determines that accrual of interest or penalties is necessary in the future, the amount will be presented as a component of income taxes.

10. Comprehensive Income (Loss)

The Company reports and presents comprehensive loss in accordance with SFAS No. 130,
Reporting Comprehensive Income, which establishes standards for reporting and display of comprehensive loss and its components in a full set of general purpose financial statements. The objective of the statement is to report a measure of all
changes in equity of an enterprise that result from transactions and other economic events of the period other than transactions with owners (comprehensive loss). The Companys other comprehensive loss arises from net unrealized gains (losses)
on marketable securities.



11



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Details relating to unrealized gains and losses and other comprehensive loss are as follows:



|                                                          |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|--------------------------------------------------------- |  | ----------------------------------- | ------ | - | --------------------------------- | - | ------ | ---- |  | - | ------- | - |  | - | ------- | -
|                                                          |  | For the Three Months Ended June 30, |        |   | For the Six Months Ended June 30, |  
|                                                          |  | 2008                                |        |   | 2007                              |   |        | 2008 |  |   | 2007    |  
|Net loss                                                  |  | $                                   | (6,789 | ) |                                   | $ | (7,653 | )    |  | $ | (12,786 | ) |  | $ | (15,322 | )
|Change in unrealized gain (loss) on marketable securities |  |                                     | (73    | ) |                                   |   | (7     | )    |  |   | (47     | ) |  |   | 14      |  
|                                                          |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  
|Total comprehensive loss                                  |  | $                                   | (6,862 | ) |                                   | $ | (7,660 | )    |  | $ | (12,833 | ) |  | $ | (15,308 | )
|                                                          |  |                                     |        |   |                                   |   |        |      |  |   |         |   |  |   |         |  

11. Recently Issued Accounting Pronouncements

In September 2006, the FASB issued SFAS No. 157, Fair Value Measurements,or SFAS No. 157. SFAS No. 157 defines fair value,
establishes a framework for measuring fair value in generally accepted accounting principles, and expands disclosures about fair value measurements. The standard is effective for financial statements issued for fiscal years beginning after
November 15, 2007 and interim periods within those fiscal years. The Company adopted SFAS No. 157 for financial assets and liabilities effective January 1, 2008. There was no impact to the Companys financial statements upon
adoption. On February 12, 2008, the FASB issued FASB Staff Position (FSP) FAS No. 157-2. This FSP permits a delay in the effective date of SFAS No. 157 to fiscal years beginning after November 15, 2008 for nonfinancial assets and
nonfinancial liabilities, except for items that are recognized or disclosed at fair value in the financial statements on a recurring basis, at least annually. The Company does not believe that its adoption of SFAS No. 157 for nonfinancial
assets and nonfinancial liabilities will have a material impact on the Companys financial statements.

In February 2007, the
FASB issued SFAS No. 159, The Fair Value Option for Financial Assets and Financial Liabilities,or SFAS No. 159. SFAS No. 159 permits an entity to elect to report many financial assets and liabilities at fair value.
Entities electing the fair value option would be required to recognize changes in fair value in earnings and are required to distinguish, on the face of the statement of financial position, the fair value of assets and liabilities for which the fair
value option has been elected and similar assets and liabilities measured using another measurement attribute. The initial adjustment to reflect the difference between the fair value and the carrying amount would be accounted for as a
cumulative-effect adjustment to retained earnings as of the date of initial adoption. SFAS No. 159 was effective as of the beginning of an entitys first fiscal year beginning after November 15, 2007. The Company did not elect to
adopt the fair value option.

In June 2007, the Emerging Issues Task Force, or EITF, reached a consensus on EITF Issue No. 07-03,
Accounting for Nonrefundable Advance Payments for Goods or Services to Be Used in Future Research and Development Activities, or EITF No. 07-03. EITF No. 07-03 concludes that non-refundable advance payments for future research and
development activities should be deferred and capitalized until the goods have been delivered or the related services have been performed. If an entity does not expect the goods to be delivered or services to be rendered, the capitalized advance
payment should be charged to expense. This consensus was effective for fiscal years beginning after December 15, 2007. The Companys adoption of EITF No. 07-03 on January 1, 2008 did not have an impact on its financial
statements.

In December 2007, the EITF reached a consensus on EITF Issue No. 07-01, Accounting for Collaborative Arrangements
Related to the Development and Commercialization of Intellectual Property, or EITF No. 07-01. EITF No. 07-01 prescribes the accounting for collaborations. It requires certain transactions between collaborators to be recorded in the
income statement on either a gross or net basis within expenses when certain characteristics exist in the collaboration relationship. EITF No. 07-01 is effective for the Companys collaborations existing after January 1, 2009. The
Company is currently evaluating the impact this standard will have on its financial statements.

In December 2007, the FASB issued
SFAS No. 141R, Business Combinations,or SFAS No. 141R, which changes the accounting for business acquisitions. SFAS No. 141R requires the acquiring entity in a business combination to recognize all the assets acquired and
liabilities assumed in the transaction and establishes the acquisition-date fair value as the measurement objective for all assets acquired and liabilities assumed in a business combination. Certain provisions of this standard will, among other
things, impact the determination of acquisition-date fair value of consideration paid in a business combination, including contingent consideration; exclude transaction costs from acquisition accounting; and change accounting practices for acquired
contingencies, acquisition-related restructuring costs, in-process research and development, indemnification assets, and tax benefits. SFAS No. 141R is effective for business combinations and adjustments to an acquired entitys
deferred tax asset and liability balances occurring after December 31, 2008. Adoption of SFAS No. 141R will have a material impact on the Companys financial position and results of operations in the event that the Company enters
into a business combination that falls within the scope of this pronouncement.



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In December 2007, the FASB issued SFAS No. 160, Noncontrolling Interests in Consolidated
Financial Statementsor SFAS No. 160, an amendment of ARB No. 51, which establishes new standards governing the accounting for and reporting of noncontrolling interests, or NCIs, in partially owned consolidated subsidiaries and the
loss of control of subsidiaries. Certain provisions of this standard indicate, among other things, that NCIs be treated as a separate component of equity, not as a liability; that increases and decreases in the parents ownership interest
that leave control intact be treated as equity transactions, rather than as step acquisitions or dilution gains or losses; and that losses of a partially owned consolidated subsidiary be allocated to the NCI even when such allocation might result in
a deficit balance. This standard also requires changes to certain presentation and disclosure requirements. SFAS No. 160 is effective for fiscal years beginning after December 31, 2008. The Company does not believe that the adoption of
SFAS No. 160 will have a material impact on our financial statements.

12. Subsequent Event

On August 12, 2008, the Company issued 10,714,655 units at a price of $2.9049 per unit, resulting in gross proceeds of $31,100 or $29,500 net of
offering expenses. Each unit consists of one share of the Companys common stock and a warrant to purchase 0.25 shares of common stock at an exercise price of $3.53 per share. The investors may have the option to purchase an additional
3,679,078 units between February 2009 and August 2009. The Company has agreed to seek stockholder approval for the securities in accordance with NASDAQ Marketplace Rules.



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|ITEM 2. | MANAGEMENTS DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS
|------- | -------------------------------------------------------------------------------------

This quarterly report on Form 10-Q contains forward-looking statements within the meaning of Section 21E of the Securities Exchange Act of 1934,
as amended, that involve risks and uncertainties. All statements other than statements relating to historical matters including statements to the effect that we believe, expect, anticipate, plan,
target, intend and similar expressions should be considered forward-looking statements. Our actual results could differ materially from those discussed in the forward-looking statements as a result of a number of important
factors, including factors discussed in this section and elsewhere in this quarterly report on Form 10-Q, including those discussed in Item 1A of this report under the heading Risk Factors, and the risks discussed in our other
filings with the Securities and Exchange Commission. Readers are cautioned not to place undue reliance on these forward-looking statements, which reflect managements analysis, judgment, belief or expectation only as the date hereof. We assume
no obligation to update these forward-looking statements to reflect events or circumstances that arise after the date hereof.

Overview

We are a biopharmaceutical company focused on the discovery, development and commercialization of innovative treatments for infectious
diseases. Within the anti-infective market, we are currently concentrating on the development of antivirals and antibacterials. We are targeting our antiviral development efforts on treatments for chronic hepatitis C and HIV infection, and we are
directing our antibacterial development efforts toward treatments for serious hospital-based bacterial infections.

We have devoted and are
continuing to devote substantially all of our efforts toward product research and development. We have incurred losses of $150.8 million from inception through June 30, 2008 and had an accumulated deficit of $164.6 million through June 30,
2008. Our net losses were $12.8 million and $15.3 million for the six months ended June 30, 2008 and 2007, respectively. We have funded our operations primarily through:



| |  |  | proceeds of $161.2 million from the sale of equity securities, including our initial public offering in October 2006;
| | - |  | ---------------------------------------------------------------------------------------------------------------------



| |  |  | borrowings of $22.1 million from debt facilities; and
| | - |  | -----------------------------------------------------



| |  |  | receipts of $10.0 million from up-front and milestone payments, as well as $8.8 million in cost-sharing receipts from our collaboration partner, Gilead Sciences.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------

We expect to incur substantial and increasing losses for at least the next several years as we seek to:



| |  |  | complete the open-label extension phases of our phase II clinical trials for elvucitabine;
| | - |  | ------------------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1095 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1625 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete our assessment of ACH-702 preclinical data and prepare for clinical testing;
| | - |  | -------------------------------------------------------------------------------------



| |  |  | advance our carbapenem compounds to identify a clinical lead candidate; and
| | - |  | ---------------------------------------------------------------------------



| |  |  | progress additional drug candidates.
| | - |  | ------------------------------------

We will need substantial additional financing to obtain regulatory approvals, fund operating losses, and, if deemed appropriate, establish manufacturing and sales and marketing capabilities, which we will seek to raise through public or
private equity or debt financings, collaborative or other arrangements with third parties or through other sources of financing. There can be no assurance that such funds will be available on terms favorable to us, if at all. In addition to the
normal risks associated with early-stage companies, there can be no assurance that we will successfully complete our research and development, obtain adequate patent protection for our technology, obtain necessary government regulatory approval for
drug candidates we develop or that any approved drug candidates will be commercially viable. In addition, we may not be profitable even if we succeed in commercializing any of our drug candidates.



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##### Table of Contents

On August 12, 2008, we issued 10,714,655 units at a price of $2.9049 per unit, resulting in gross
proceeds of $31.1 million, or $29.5 million net of offering expenses. Each unit consists of one share of our common stock and a warrant to purchase 0.25 shares of common stock at an exercise price of $3.53 per share. The investors may have the
option to purchase an additional 3,679,078 units between February 2009 and August 2009. We have agreed to seek stockholder approval for the securities in accordance with NASDAQ Marketplace Rules.

Financial Operations Overview

Revenue

To date, we have not generated revenue from the sale of any drugs. The majority of our revenue recognized to date has been derived from our
collaboration with Gilead Sciences to develop compounds for use in treating chronic hepatitis C infection. During the six months ended June 30, 2008 and 2007, we recognized $1.0 million and $2.7 million, respectively, under this collaboration
arrangement.

Upon initiating our collaboration with Gilead Sciences, we received a payment of $10.0 million, which included an equity
investment by Gilead Sciences determined to be worth approximately $2.0 million. The remaining $8.0 million is being accounted for as a nonrefundable up-front fee recognized under the proportionate performance model. Revenue under the proportionate
performance model is recognized as our effort under the collaboration is incurred. When our performance obligation is complete, we will recognize milestone payments, if any, when the corresponding milestone is achieved. We will recognize royalty
payments, if any, upon product sales.

Effective April 1, 2007, each party provides for the costs of their own full-time equivalents.
External research costs continue to be shared equally by both parties. Through March 31, 2007 research and development expenses under our collaboration with Gilead Sciences, including internal full-time equivalent costs and external research
costs, incurred by both companies prior to proof-of-concept, were borne equally by both parties. As we were providing the majority of those services and were incurring the majority of those expenses, we were the net recipient of funds under this
cost-sharing portion of the arrangement and therefore recognized the reimbursed costs as revenue rather than research expense. Payments made by us to Gilead Sciences in connection with this collaboration are being recognized as a reduction of
revenue.

Research and Development

Our research and development expenses reflect costs incurred for our proprietary research and development projects as well as costs for research and development projects conducted as part of collaborative
arrangements. These costs consist primarily of salaries and benefits for our research and development personnel, costs of services by clinical research organizations, other outsourced research, materials used during research and development
activities, facility-related costs such as rent and utilities associated with our laboratory and clinical development space and operating supplies. We expect that our research and development expenses will remain substantially unchanged for the
remainder of the year.

We have established our drug candidate pipeline through our internal discovery capabilities and through the
in-licensing of attractive drug candidates. Through these efforts we have identified and are developing candidates in the following areas:



| |  |  | Elvucitabine for HIV Infection. Elvucitabine is an antiviral we are developing for the treatment of HIV infection. We are currently evaluating elvucitabine
in phase II clinical trials to further explore its safety and efficacy in HIV-infected patients. We currently retain full development and marketing rights to elvucitabine. However, we are currently in discussions with potential collaboration
partners for elvucitabine and do not plan to advance elvucitabine into Phase III clinical trials without a collaboration partner.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | ACH-1095, an NS4A Antagonist for Chronic Hepatitis C Infection. We are evaluating ACH-1095 for the treatment of chronic hepatitis C in collaboration with
Gilead Sciences. ACH-1095 is currently in late-stage pre-clinical studies and we anticipate filing an investigational new drug application, or IND, for this compound during 2008.
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | ACH-1625, a Protease Inhibitor for Chronic Hepatitis C Infection. In a proprietary research program targeting HCV protease, we are also evaluating ACH-1625,
which was discovered by our internal research team. ACH-1625 has demonstrated strong in vitro potency and a satisfactory early safety profile. We have recently begun preparations for late-stage pre-clinical studies and we anticipate filing an IND
for this compound in the first half of 2009.
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| |  |  | ACH-702 for Serious Hospital-Based Bacterial Infections. ACH-702 is a preclinical candidate with potency against a broad spectrum of bacterial pathogens
including methicillin-resistant staphylococcus aureus, or MRSA, which we are developing for the treatment of serious hospital-based bacterial infections. We have scheduled a pre-IND development meeting with the FDA during the third quarter to
discuss the most appropriate clinical strategy for this candidate. Following this meeting, if appropriate based upon the outcome of those discussions, we plan to file an IND.
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

All costs associated with internal research and development, and research and development services for which we have externally contracted, are expensed
as incurred. The costs of obtaining patents for our candidates are expensed as incurred as indirect costs.



|                                                  |  |                           |        |      |   |       
|------------------------------------------------- |  | ------------------------- | ------ | ---- | - | ------
|                                                  |  | Six Months Ended June 30,
|                                                  |  | 2008                      |        | 2007
|Direct external costs:                            |  |                           |        |      |   |       
|Elvucitabine                                      |  | $                         | 1,966  |      | $ | 6,220 
|NS4A antagonists (including ACH-1095 and ACH-806) |  |                           | 539    |      |   | 1,193 
|ACH-1625                                          |  |                           | 740    |      |   |      
|ACH-702                                           |  |                           | 138    |      |   | 2,392 
|                                                  |  |                           |        |      |   |       
|                                                  |  |                           | 3,383  |      |   | 9,805 
|Direct internal personnel costs                   |  |                           | 3,891  |      |   | 3,712 
|                                                  |  |                           |        |      |   |       
|Sub-total direct costs                            |  |                           | 7,274  |      |   | 13,517
|Indirect costs and overhead                       |  |                           | 3,207  |      |   | 2,568 
|                                                  |  |                           |        |      |   |       
|Total research and development                    |  | $                         | 10,481 |      | $ | 16,085
|                                                  |  |                           |        |      |   |       

Currently, we are completing the open-label extension phases of two phase II clinical trials for
elvucitabine and conducting preclinical studies for ACH-1095 and ACH-1625. From inception through June 30, 2008, we incurred approximately $47.5 million in total costs for elvucitabine, approximately $28.0 million in total costs for our NS4A
antagonist program, including both ACH-1095 and ACH-806, approximately $5.8 million for ACH-1625 and approximately $17.4 million in total costs for ACH-702. These figures include our internal research and development personnel costs and related
facilities overhead. We currently estimate that the clinical trial costs for two phase III clinical trials of elvucitabine in different HIV populations will be approximately $50.0 million, exclusive of the internal personnel costs associated with
conducting these trials; however, we currently do not plan to undertake these trials or incur these costs without entering a collaboration agreement. We estimate that the costs associated with completing phase I clinical trials for ACH-702 will be
approximately $2.0 million, exclusive of the internal personnel costs associated with conducting these studies and trials. We anticipate that the costs associated with preclinical and early clinical development through proof-of-concept of ACH-1095,
our next generation NS4A antagonist, will be approximately $2.7 million, exclusive of internal personnel costs. This amount represents one-half of the external costs associated with those activities, as we share such external costs with Gilead
Sciences. We estimate that the costs associated with preclinical and early clinical development of ACH-1625, our HCV protease inhibitor, will be approximately $3.1 million.

General and Administrative

Our general and administrative expenses consist primarily of salaries and benefits for management and administrative personnel, professional fees for legal, accounting and other services, travel costs and facility-related costs such as
rent, utilities and other general office expenses. We expect that general and administrative expenses will remain substantially unchanged over the next twelve months.

Critical Accounting Policies and Estimates

The discussion and analysis of our financial condition
and results of operations set forth below are based on our financial statements, which have been prepared in accordance with accounting principles generally accepted in the United



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States, or U.S. GAAP. The preparation of these financial statements requires us to make estimates and assumptions that affect the reported amounts of assets
and liabilities and disclosure of contingent liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, we evaluate our estimates and assumptions, including
those described below. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable under the circumstances. These estimates and assumptions form the basis for making judgments about the carrying
values of assets and liabilities that are not readily apparent from other sources. Management makes estimates and exercises judgment in revenue recognition, research and development costs, stock-based compensation, accrued expenses and income taxes.
Actual results may differ from these estimates under different assumptions or conditions.

We believe the following critical accounting
policies affect managements more significant judgments and estimates used in the preparation of our financial statements:

Revenue Recognition

We recognize revenue from contract research and development and research progress payments in
accordance with Staff Accounting Bulletin No. 104, Revenue Recognition, or SAB No. 104, and Financial Accounting Standards Board, or FASB, Emerging Issue Task Force, or EITF, Issue No. 00-21, Accounting for Revenue Arrangements
with Multiple Deliverables, or EITF No. 00-21. Revenue-generating research and development collaborations are often multiple element arrangements, providing for a license as well as research and development services. Such arrangements are
analyzed to determine whether the deliverables, including research and development services, can be separated or whether they must be accounted for as a single unit of accounting in accordance with EITF No. 00-21. We recognize upfront license
payments as revenue upon delivery of the license only if the license has standalone value and the fair value of the undelivered performance obligations can be determined. If the fair value of the undelivered performance obligations can be
determined, such obligations would then be accounted for separately as performed. If the license is considered to either (i) not have standalone value or (ii) have standalone value but the fair value of any of the undelivered performance
obligations cannot be determined, the arrangement would then be accounted for as a single unit of accounting and the upfront license payments are recognized as revenue over the estimated period of when our performance obligations are performed.

When we determine that an arrangement should be accounted for as a single unit of accounting, we must determine the period over which the
performance obligations will be performed and revenue related to upfront license payments will be recognized. Revenue will be recognized using either a proportionate performance or straight-line method. We recognize revenue using the proportionate
performance method provided that we can reasonably estimate the level of effort required to complete our performance obligations under an arrangement and such performance obligations are provided on a best-efforts basis. Under the proportionate
performance method, periodic revenue related to up-front license payments is recognized as the percentage of actual effort expended in that period to total effort expected for all of our performance obligations under the arrangement. Actual effort
is generally determined based upon actual direct labor hours or full-time equivalents incurred and include research and development activities performed by internal scientists. Total expected effort is generally based upon the total direct labor
hours of full-time equivalents incorporated into the detailed budget and project plan that is agreed to by both parties to the collaboration. Significant management judgment is required in determining the level of effort required under an
arrangement and the period over which we expect to complete the related performance obligations. For example, under our arrangement with Gilead Sciences, the joint research committee periodically reviews and updates the project plan. In the event
that a change in estimate occurs, the change will be accounted for using the cumulative catch-up method which provides for an adjustment to revenue in the current period. Estimates of our level of effort may change in the future, resulting in a
material change in the amount of revenue recognized in future periods. We revised our joint research program with Gilead Sciences in the first quarter of 2007 to focus on next-generation NS4A antagonists. At that time, we extended the period over
which our remaining obligations under the arrangement would be completed. In addition, we and Gilead Sciences agreed to continue to equally share external costs, but effective April 1, 2007, internal full-time equivalents would no longer be
subject to a cost sharing arrangement. Instead, each party bears the costs of their respective full-time equivalents.

Generally under
collaboration arrangements, payments received during the period of performance may include up-front payments, time-or performance-based milestones and reimbursement of internal and external costs. The proportion of actual performance to total
expected performance is applied to these payments in determining periodic revenue, but will be limited by the aggregate cash received or receivable to date by us.

Substantive milestone payments are considered to be performance bonuses that are recognized upon achievement of the milestone only if all of the following conditions are met: (1) the milestone payments are
non-refundable, (2) achievement of the milestone involves a degree of risk and was not reasonably assured at the inception of the arrangement, (3) substantive



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effort is involved in achieving the milestone, (4) the amount of the milestone payment is reasonable in relation to the effort expended or the risk
associated with achievement of the milestone and (5) a reasonable amount of time passes between the upfront license payment and the first milestone payment as well as between each subsequent milestone payment.

Reimbursement of costs is recognized as revenue provided the provisions of EITF Issue No. 99-19, Reporting Revenue Gross as Principal Versus Net
as an Agent, are met, the amounts are determinable and collection of the related receivable is reasonably assured.

Stock-Based
Compensation  Employee Stock-Based Awards

We apply the Statement of Financial Accounting Standards No. 123 as revised in
2004, Share-Based Payment, or SFAS No. 123R, which requires measurement and recognition of compensation expense for all stock-based awards made to employees and directors, including employee stock options and employee stock purchases
under our 2006 ESPP Plan based on estimated fair values. In December 2007, the SEC issued Staff Accounting Bulletin No. 110, or SAB No. 110, which extends the use of the simplified method in developing an estimate of the expected term of
plain vanilla share options beyond December 31, 2007. We utilize the provisions of SAB No. 110 in our application of SFAS No. 123R.

We primarily grant qualified stock options for a fixed number of shares to employees with an exercise price equal to the market value of the shares at the date of grant. To the extent that the amount of the aggregate
fair market value of qualified stock options that become exercisable for an individual exceeds $100,000 during any tax year, those stock options are treated as non qualified stock options. Under the fair value recognition provisions of SFAS
No. 123R, stock-based compensation cost is based on the value of the portion of stock-based awards that is ultimately expected to vest during the period. Stock-based compensation expense recognized during the six months ended June 30, 2008
and 2007 includes compensation expense for stock-based awards granted prior to, but not yet vested as of December 31, 2005, based on the fair value on the grant date estimated in accordance with the pro forma provisions of SFAS No. 123.
Compensation expense also includes amounts related to the stock-based awards granted subsequent to December 31, 2005, based on the fair value on the grant date, estimated in accordance with the provisions of SFAS No. 123R.

We utilize the Black-Scholes option pricing model for determining the estimated fair value for stock-based awards. The Black-Scholes model requires the
use of assumptions which determine the fair value of the stock-based awards. Determining the fair value of stock-based awards at the grant date requires judgment, including estimating the expected term of stock options, the expected volatility of
our stock and expected dividends. In addition, we previously accounted for forfeitures as they occurred. In accordance with SFAS No. 123R, we are required to estimate forfeitures at the grant date and recognize compensation costs for only those
awards that are expected to vest. Judgment is required in estimating the amount of stock-based awards that are expected to be forfeited.

If factors change and we employ different assumptions in the application of SFAS No. 123R in future periods, the compensation expense that we record under SFAS No. 123R may differ significantly from what we have recorded in the
current period. Therefore, we believe it is important for investors to be aware of the degree of subjectivity involved when using option pricing models to estimate share-based compensation under SFAS No. 123R. There is risk that our estimates
of the fair values of our share-based compensation awards on the grant dates may differ from the actual values realized upon the exercise, expiration, early termination or forfeiture of those share-based payments in the future. Certain share-based
payments, such as employee stock options, may expire worthless or otherwise result in zero intrinsic value as compared to the fair values originally estimated on the grant date and reported in our financial statements. Alternatively, value may be
realized from these instruments that is significantly in excess of the fair values originally estimated on the grant date and reported in our financial statements. Although the fair value of employee share-based awards is determined in accordance
with SFAS No. 123R and SAB No. 110 using an option pricing model, that value may not be indicative of the fair value observed in a willing buyer/willing seller market transaction.

Accrued Expenses

As part of
the process of preparing financial statements, we are required to estimate accrued expenses. This process involves identifying services which have been performed on our behalf and estimating the level of service performed and the associated cost
incurred for such service as of each balance sheet date in our financial statements.

In accruing service fees, we estimate the time period
over which services will be provided and the level of effort in each period. If the actual timing of the provision of services or the level of effort varies from the estimate, we will adjust the



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accrual accordingly. The majority of our service providers invoice us monthly in arrears for services performed. Some of our service providers require
upfront or milestone payments. If our estimate of services performed is less than the upfront or milestone payments, the difference is accounted for as a prepaid expense. In the event that we do not identify costs that have been incurred or we
underestimate or overestimate the level of services performed or the costs of such services, our actual expenses could differ from such estimates. The date on which some services commence, the level of services performed on or before a given date
and the cost of such services are often subjective determinations. We make judgments based upon facts and circumstances known to us in accordance with U.S. GAAP.

Income Taxes

We use an asset and liability approach for financial accounting and reporting of
income taxes. Deferred tax assets and liabilities are determined based on temporary differences between financial reporting and tax basis assets and liabilities and are measured by applying enacted rates and laws to taxable years in which
differences are expected to be recovered or settled. Further, the effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that the rate changes.

Effective January 1, 2007, we adopted Financial Accounting Standards Board (FASB) Interpretation No. 48, Accounting for
Uncertainty in Income Taxesan interpretation of FASB Statement No. 109,or FIN 48. FIN 48 prescribes a comprehensive model for how a company should recognize, measure, present, and disclose in its financial statements uncertain
tax positions that the company has taken or expects to take on a tax return, including a decision whether to file or not file a return in a particular jurisdiction. Under FIN 48, the financial statements reflect expected future tax consequences of
such positions presuming the taxing authorities full knowledge of the position and all relevant facts.

We do not have any
unrecognized tax benefits as of the date of adoption or June 30, 2008. We review all tax positions to ensure the tax treatment selected is sustainable based on its technical merits and that the position would be sustained if challenged.

Results of Operations

Results of
operations may vary from period to period depending on numerous factors, including the timing of payments received under existing or future strategic alliances, joint ventures or financings, if any, the progress of our research and development
projects, technological advances and determinations as to the commercial potential of proposed products.

Comparison of Three and Six
Months Ended June 30, 2008 and 2007

Revenue. Revenue was $398,000 and $1.2 million for the three months ended
June 30, 2008 and 2007, and $1.0 million and $2.7 million for the six months ended June 30, 2008 and 2007, respectively. The decrease in revenue in 2008 is primarily due to a decrease in full time equivalent, or FTE, hours we expended
under the collaboration arrangement with Gilead in 2008, which is the basis of our proportionate performance calculation. Under the proportionate performance method, periodic revenue related to up-front license payments is recognized as the
percentage of actual effort expended in that period to total effort expected for all of our performance obligations under the arrangement. This decrease is combined with a decrease in external costs incurred. During the first quarter of 2007, we
recognized revenue under a Small Business Innovation Research, or SBIR, grant. No additional grant revenue related to this grant will be recognized. Revenue consisted of the following:



|                             |  |                             |     |      |                           |        |  |      |      |  |      |       |        |   |       |  |   |        |  
|---------------------------- |  | --------------------------- | --- | ---- | ------------------------- | ------ |  | ---- | ---- |  | ---- | ----- | ------ | - | ----- |  | - | ------ | -
|                             |  | Three Months Ended June 30, |     |      | Six Months Ended June 30, |       
|                             |  | 2008                        |     | 2007 |                           | Change |  |      | 2008 |  | 2007 |       | Change |  
|                             |  | (in thousands)              |     |      | (in thousands)            |       
|Gilead collaboration revenue |  | $                           | 398 |      | $                         | 1,195  |  | (797 | )    |  | $    | 1,025 |        | $ | 2,710 |  | $ | (1,685 | )
|Grant revenue                |  |                             |    |      |                           |       |  |     |      |  |      |      |        |   | 35    |  |   | (35    | )
|                             |  |                             |     |      |                           |        |  |      |      |  |      |       |        |   |       |  |   |        |  
|Total revenue                |  | $                           | 398 |      | $                         | 1,195  |  | (797 | )    |  | $    | 1,025 |        | $ | 2,745 |  | $ | (1,720 | )
|                             |  |                             |     |      |                           |        |  |      |      |  |      |       |        |   |       |  |   |        |  



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Through the completion of our performance obligations under the collaboration with Gilead in 2009, we
expect to recognize additional revenue of approximately $1.7 million, offset by any payments we are obligated to make to Gilead Sciences in satisfaction of external costs paid by Gilead Sciences under our external cost-sharing arrangement. It is
possible that we will recognize negative revenue in future quarters based upon the timing of our performance under the collaboration, and on the timing and magnitude of external costs borne by Gilead Sciences.

Research and Development Expenses. Research and development expenses were $5.5 million and $7.7 million for the three months ended June 30,
2008 and 2007, respectively, and $10.5 million and $16.1 million for the six months ended June 30, 2008 and 2007, respectively. The decrease in 2008 was primarily due to lower outsourced research costs related to phase II trials for
elvucitabine and the completion of preclinical testing of ACH-702 in 2007, partially offset by increased scientific consulting fees and the upfront license fee under our collaboration with FOB Synthesis for the six months ended June 30, 2008.
We expect that research and development expenses during the remainder of 2008 will remain substantially unchanged from the first half of 2008. Research and development expenses for the three and six months ended June 30, 2008 and 2007 are
comprised as follows:



|                                 |  |                             |       |      |                           |        |  |   |        |   |      |   |        |  |   |        |  |   |        |  
|-------------------------------- |  | --------------------------- | ----- | ---- | ------------------------- | ------ |  | - | ------ | - | ---- | - | ------ |  | - | ------ |  | - | ------ | -
|                                 |  | Three Months Ended June 30, |       |      | Six Months Ended June 30, |       
|                                 |  | 2008                        |       | 2007 |                           | Change |  |   | 2008   |   | 2007 |   | Change | 
|Personnel costs                  |  | $                           | 1,637 |      | $                         | 1,645  |  | $ | (8     | ) |      | $ | 3,387  |  | $ | 3,424  |  | $ | (37    | )
|Stock based compensation         |  |                             | 220   |      |                           | 134    |  |   | 86     |   |      |   | 518    |  |   | 292    |  |   | 226    |  
|Outsourced research and supplies |  |                             | 2,437 |      |                           | 4,661  |  |   | (2,224 | ) |      |   | 4,070  |  |   | 9,995  |  |   | (5,925 | )
|Professional and consulting fees |  |                             | 462   |      |                           | 550    |  |   | (88    | ) |      |   | 1,004  |  |   | 875    |  |   | 129    |  
|Facilities costs                 |  |                             | 664   |      |                           | 643    |  |   | 21     |   |      |   | 1,387  |  |   | 1,321  |  |   | 66     |  
|Travel and other costs           |  |                             | 63    |      |                           | 86     |  |   | (23    | ) |      |   | 115    |  |   | 178    |  |   | (63    | )
|                                 |  |                             |       |      |                           |        |  |   |        |   |      |   |        |  |   |        |  |   |        |  
|Total                            |  | $                           | 5,483 |      | $                         | 7,719  |  | $ | (2,236 | ) |      | $ | 10,481 |  | $ | 16,085 |  | $ | (5,604 | )
|                                 |  |                             |       |      |                           |        |  |   |        |   |      |   |        |  |   |        |  |   |        |  

General and Administrative Expenses. General and administrative expenses were $1.6 million
and $1.7 million for the three months ended June 30, 2008 and 2007, respectively and $3.3 million and $3.3 million for the six months ended June 30, 3008 and 2007, respectively. The decrease for the three months ended June 30, 2008
was primarily due to certain market studies performed during 2007 that were not repeated in 2008. We expect that general and administrative expenses will remain substantially unchanged over the next twelve months. General and administrative expenses
for the three and six months ended June 30, 2008 and 2007 are comprised as follows:



|                                 |  |                             |       |      |                           |        |  |   |      |   |      |   |        |  |   |       |  |   |     |  
|-------------------------------- |  | --------------------------- | ----- | ---- | ------------------------- | ------ |  | - | ---- | - | ---- | - | ------ |  | - | ----- |  | - | --- | -
|                                 |  | Three Months Ended June 30, |       |      | Six Months Ended June 30, |       
|                                 |  | 2008                        |       | 2007 |                           | Change |  |   | 2008 |   | 2007 |   | Change | 
|Personnel costs                  |  | $                           | 440   |      | $                         | 482    |  | $ | (42  | ) |      | $ | 976    |  | $ | 1,010 |  | $ | (34 | )
|Stock based compensation         |  |                             | 307   |      |                           | 266    |  |   | 41   |   |      |   | 575    |  |   | 519   |  |   | 56  |  
|Professional and consulting fees |  |                             | 401   |      |                           | 530    |  |   | (129 | ) |      |   | 832    |  |   | 866   |  |   | (34 | )
|Facilities costs                 |  |                             | 312   |      |                           | 302    |  |   | 10   |   |      |   | 606    |  |   | 567   |  |   | 39  |  
|Travel and other costs           |  |                             | 148   |      |                           | 143    |  |   | 5    |   |      |   | 307    |  |   | 309   |  |   | (2  | )
|                                 |  |                             |       |      |                           |        |  |   |      |   |      |   |        |  |   |       |  |   |     |  
|Total                            |  | $                           | 1,608 |      | $                         | 1,723  |  | $ | (115 | ) |      | $ | 3,296  |  | $ | 3,271 |  | $ | 25  |  
|                                 |  |                             |       |      |                           |        |  |   |      |   |      |   |        |  |   |       |  |   |     |  



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Other Income (Expense). Interest income was $162,000 and $666,000 for three months ended
June 30, 2008 and 2007, respectively. The decrease was primarily due to decreased average cash balances combined with lower interest rates. Interest expense was $308,000 and $242,000 for the three months ended June 30, 2008 and 2007,
respectively. The increase was primarily due to interest related to the $5.0 million obtained under the 2008 credit facility in February 2008. Interest income was $453,000 and $1.4 million for six months ended June 30, 2008 and 2007,
respectively. The decrease was primarily due to decreased average cash balances combined with lower interest rates. Interest expense was $559,000 and $506,000 for the six months ended June 30, 2008 and 2007, respectively. The increase was
primarily due to interest related to the $5.0 million obtained under the 2008 credit facility in February 2008.

Tax Benefit. The
State of Connecticut provides companies with the opportunity to forego certain research and development tax credit carryforwards in exchange for cash. The program provides for such exchange of the research and development credits at a rate of 65% of
the annual incremental and non-incremental research and development credits, as defined. The amount of tax benefit we recognized in connection with this exchange program was $50,000 and $170,000 for the three months ended June 30, 2008 and
2007, respectively. The amount of tax benefit we recognized in connection with this exchange program was $72,000 and $371,000 for the six months ended June 30, 2008 and 2007, respectively. The decreases from 2007 to 2008 were due to the
decrease in eligible research and development costs, resulting primarily from near completion of elvucitabine phase II trials and reduced preclinical costs associated with ACH-702.

Liquidity and Capital Resources

Since our inception in August 1998, we have financed our operations
primarily through our initial public offering, the issuance of our convertible preferred stock, borrowings under debt facilities, as well as through receipts from our collaboration with Gilead Sciences. Through June 30, 2008, we had received
approximately $161.2 million in aggregate net proceeds from stock issuances, including convertible preferred stock and our initial public offering, $18.8 million from Gilead Sciences under our collaboration agreement with them and approximately
$22.1 million under the following debt facilities:



|                                     |  |               |  |                          |  |                 |           |               |                    
|------------------------------------ |  | ------------- |  | ------------------------ |  | --------------- | --------- | ------------- | -------------------
|Lender                               |  | Date          |  | Interest Rate(per annum) |  | PrincipalAmount |           | Maturity Date
|Connecticut Innovations, Inc.        |  | November 2000 |  | 7.5%                     |  | $               | 1,400,000 |               | September 2010     
|Connecticut Innovations, Inc.        |  | May 2002      |  | 7.5%                     |  | $               | 278,000   |               | October 2007       
|General Electric Capital Corporation |  | March 2002    |  | 8.01% -10.17%            |  | $               | 3,264,182 |               | March 2005-May 2007
|Webster Bank                         |  | May 2003      |  | 6.72% -  9.27%           |  | $               | 972,185   |               | June 2006-Dec 2009 
|Oxford Finance Corporation           |  | December 2005 |  | 10.92%                   |  | $               | 2,500,000 |               | November 2008      
|General Electric Capital Corporation |  | December 2005 |  | 10.92%                   |  | $               | 2,500,000 |               | November 2008      
|Oxford Finance Corporation           |  | May 2006      |  | 11.56%                   |  | $               | 2,500,000 |               | April 2009         
|General Electric Capital Corporation |  | May 2006      |  | 11.56%                   |  | $               | 2,500,000 |               | April 2009         
|Oxford Finance Corporation           |  | June 2007     |  | 11.58%                   |  | $               | 400,000   |               | June 2010          
|General Electric Capital Corporation |  | June 2007     |  | 11.58%                   |  | $               | 400,000   |               | June 2010          
|Webster Bank                         |  | December 2007 |  | 7.46%                    |  | $               | 414,623   |               | December 2010      
|Oxford Finance Corporation           |  | February 2008 |  | 9.97%                    |  | $               | 2,500,000 |               | March 2011         
|General Electric Capital Corporation |  | February 2008 |  | 9.97%                    |  | $               | 2,500,000 |               | March 2011         

The amounts reflected above represent original maturities under our debt agreements. As of
June 30, 2008, our debt balance due to borrowings is $9.1 million with a weighted average interest rate of 10.36%.

On August 12,
2008, we issued 10,714,655 units at a price of $2.9049 per unit, resulting in gross proceeds of $31.1 million, or $29.5 million net of offering expenses. Each unit consists of one share of our common stock and a warrant to purchase 0.25 shares of
common stock at an exercise price of $3.53 per share. The investors may have the option to purchase an additional 3,679,078 units between February 2009 and August 2009. We have agreed to seek stockholder approval for the securities in accordance
with NASDAQ Marketplace Rules.

We had $22.0 million and $31.1 million in cash, cash equivalents and marketable securities as of
June 30, 2008 and December 31, 2007, respectively.



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Cash used in operating activities was $11.9 million for the six months ended June 30, 2008 and was
primarily attributable to our $12.8 million net loss and a decrease in deferred revenue primarily offset by non-cash charges related to depreciation, amortization and non-cash stock based compensation. Cash used in operating activities was $14.0
million for the six months ended June 30, 2007 and was primarily attributable to our $15.3 million net loss, primarily offset by a decrease in working capital and non-cash charges related to depreciation, amortization and non-cash stock based
compensation.

Cash provided by investing activities was $11.1 million for the six months ended June 30, 2008 and was primarily
attributable to the maturities of marketable securities offset by purchases of marketable securities. Cash provided by investing activities was $1.6 million for the six months ended June 30, 2007 and was primarily attributable to the maturities
of marketable securities offset by purchases of marketable securities and capital improvements.

Cash provided by financing activities was
$2.5 million for the six months ended June 30, 2008 and was primarily attributable to $5.0 million in borrowing under our 2008 credit facility, offset by repayments of debt. Cash used in financing activities was $752,000 for the six months
ended June 30, 2007 and was primarily attributable to $1.8 million used for repayments of debt offset by $800,000 in proceeds under our 2003 credit facility.

We expect to incur continuing and increasing losses from operations for at least the next several years as we seek to:



| |  |  | complete the open-label extension phases of our phase II clinical trials for elvucitabine;
| | - |  | ------------------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1095 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1625 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete our assessment of ACH-702 preclinical data and prepare for early clinical testing;
| | - |  | -------------------------------------------------------------------------------------------



| |  |  | advance our carbapenem compounds to identify a clinical lead candidate; and
| | - |  | ---------------------------------------------------------------------------



| |  |  | progress additional drug candidates.
| | - |  | ------------------------------------

We do not expect our existing capital resources, together with the milestone payments and research and development funding we expect to receive, to be sufficient to fund the completion of the development of any of our drug candidates. As a
result, we will need to raise additional funds prior to being able to market any drug candidates, to, among other things, obtain regulatory approvals, fund operating losses, and, if deemed appropriate, establish manufacturing and sales and marketing
capabilities. We will seek to raise such additional financing through public or private equity or debt financings, collaborative or other arrangements with third parties or through other sources of financing.

We believe that our existing cash and cash equivalents will be sufficient to meet our projected operating requirements for at least the next twelve
months. However, our funding resources and requirements may change and will depend upon numerous factors, including but not limited to:



| |  |  | the costs involved in the preclinical and clinical development, manufacturing and formulation of elvucitabine, ACH-1625 and ACH-702;
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the costs involved in the preclinical and clinical development of ACH-1095 and other NS4A antagonists, certain portions of which we share with Gilead Sciences;
| | - |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our ability to enter into corporate collaborations and the terms and success of these collaborations;
| | - |  | -----------------------------------------------------------------------------------------------------



| |  |  | the costs involved in obtaining regulatory approvals for our drug candidates;
| | - |  | -----------------------------------------------------------------------------



| |  |  | the scope, prioritization and number of programs we pursue;
| | - |  | -----------------------------------------------------------



| |  |  | the costs involved in preparing, filing, prosecuting, maintaining, enforcing and defending patent and other intellectual property claims;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our ability to raise incremental debt or equity capital;
| | - |  | --------------------------------------------------------



| |  |  | our ability to obtain stockholder approval for our August 2008 financing;
| | - |  | -------------------------------------------------------------------------



| |  |  | our acquisition and development of new technologies and drug candidates; and
| | - |  | ----------------------------------------------------------------------------



| |  |  | competing technological and market developments currently unknown to us.
| | - |  | ------------------------------------------------------------------------



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Off-Balance Sheet Arrangements

We do not have any off-balance sheet arrangements or relationships with unconsolidated entities or financial partnerships, such as entities often referred to as structured finance or special purpose entities.

Recently Issued Accounting Pronouncements

In September 2006, the FASB issued SFAS No. 157, Fair Value Measurements. SFAS No. 157 defines fair value, establishes a framework for measuring fair value in generally accepted accounting principles, and expands
disclosures about fair value measurements. The standard is effective for financial statements issued for fiscal years beginning after November 15, 2007 and interim periods within those fiscal years. We adopted SFAS No. 157 for financial
assets and liabilities effective January 1, 2008. There was no impact to our financial statements upon adoption. On February 12, 2008, the FASB issued FASB Staff Position (FSP) FAS No. 157-2. This FSP permits a delay in the effective
date of SFAS No. 157 to fiscal years beginning after November 15, 2008, for nonfinancial assets and nonfinancial liabilities, except for items that are recognized or disclosed at fair value in the financial statements on a recurring basis,
at least annually. We do not believe that adoption of SFAS No. 157 for nonfinancial assets and nonfinancial liabilities will have a material impact on our financial statements.

In February 2007, the FASB issued SFAS No. 159, The Fair Value Option for Financial Assets and Financial Liabilities, or SFAS
No. 159. SFAS No. 159 permits an entity to elect to report many financial assets and liabilities at fair value. Entities electing the fair value option would be required to recognize changes in fair value in earnings and are required to
distinguish, on the face of the statement of financial position, the fair value of assets and liabilities for which the fair value option has been elected and similar assets and liabilities measured using another measurement attribute. The initial
adjustment to reflect the difference between the fair value and the carrying amount would be accounted for as a cumulative-effect adjustment to retained earnings as of the date of initial adoption. SFAS No. 159 was effective as of the beginning
of an entitys first fiscal year beginning after November 15, 2007. We did not elect to adopt the fair value option.

In June
2007, the Emerging Issues Task Force, or EITF, reached a consensus on EITF Issue No. 07-03, Accounting for Nonrefundable Advance Payments for Goods or Services to Be Used in Future Research and Development Activities, or EITF
No. 07-03. EITF No. 07-03 concludes that non-refundable advance payments for future research and development activities should be deferred and capitalized until the goods have been delivered or the related services have been performed. If
an entity does not expect the goods to be delivered or services to be rendered, the capitalized advance payment should be charged to expense. This consensus was effective for fiscal years beginning after December 15, 2007. The adoption of EITF
No. 07-03 in the first quarter of 2008 did not have an impact on our financial statements.

In December 2007, the EITF reached a
consensus on EITF Issue No. 07-01, Accounting for Collaborative Arrangements Related to the Development and Commercialization of Intellectual Property, or EITF No. 07-01. EITF No. 07-01 prescribes the accounting for
collaborations. It requires certain transactions between collaborators to be recorded in the income statement on either a gross or net basis within expenses when certain characteristics exist in the collaboration relationship. EITF No. 07-01 is
effective for our collaborations existing after January 1, 2009. We are currently evaluating the impact this standard will have on our financial statements.

In December 2007, the FASB issued SFAS No. 141R, Business Combinations, which changes the accounting for business acquisitions. SFAS No. 141R requires the acquiring entity in a business
combination to recognize all the assets acquired and liabilities assumed in the transaction and establishes the acquisition-date fair value as the measurement objective for all assets acquired and liabilities assumed in a business
combination. Certain provisions of this standard will, among other things, impact the determination of acquisition-date fair value of consideration paid in a business combination, including contingent consideration; exclude transaction costs
from acquisition accounting; and change accounting practices for acquired contingencies, acquisition-related restructuring costs, in-process research and development, indemnification assets, and tax benefits. SFAS No. 141R is effective for
business combinations and adjustments to an acquired entitys deferred tax asset and liability balances occurring after December 31, 2008. Adoption of SFAS No. 141R will likely have a material impact on our financial position and
results of operations in the event that we enter into a business combination that falls within the scope of this pronouncement.



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In December 2007, the FASB issued SFAS No. 160, Noncontrolling Interests in Consolidated
Financial Statements, an amendment of ARB No. 51, which establishes new standards governing the accounting for and reporting of noncontrolling interests, or NCIs, in partially owned consolidated subsidiaries and the loss of control of
subsidiaries. Certain provisions of this standard indicate, among other things, that NCIs be treated as a separate component of equity, not as a liability; that increases and decrease in the parents ownership interest that leave control
intact be treated as equity transactions, rather than as step acquisitions or dilution gains or losses; and that losses of a partially owned consolidated subsidiary be allocated to the NCI even when such allocation might result in a deficit balance.
This standard also requires changes to certain presentation and disclosure requirements. SFAS No. 160 is effective for fiscal years beginning after December 31, 2008. We do not believe that our adoption of SFAS No. 160 will have a
material impact on our financial statements.



|ITEM 3. | QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK
|------- | ----------------------------------------------------------

Interest Rate Risk. Our exposure to market risk is confined to our cash, cash equivalents and marketable securities. We invest in high-quality financial instruments, primarily money market funds, federal agency notes, corporate debt
securities and U.S. treasury notes, with the effective duration of the portfolio less than six months and no security with an effective duration in excess of 12 months, which we believe are subject to limited credit risk. We currently do not hedge
interest rate exposure. Due to the short-term nature of our investments, we do not believe that we have any material exposure to interest rate risk or changes in credit ratings arising from our investments.

Capital Market Risk. We currently have no product revenues and depend on funds raised through other sources. One source of funding
is through future equity offerings. Our ability to raise funds in this manner depends upon capital market forces affecting our stock price.



|ITEM 4. | CONTROLS AND PROCEDURES
|------- | -----------------------

Our management, with the
participation of our chief executive officer and chief financial officer, evaluated the effectiveness of our disclosure controls and procedures as of June 30, 2008. The term disclosure controls and procedures, as defined in
Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, or the Exchange Act, means controls and other procedures of a company that are designed to ensure that information required to be disclosed by a company in the reports
that it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the SECs rules and forms. Disclosure controls and procedures include, without limitation, controls and
procedures designed to ensure that information required to be disclosed by a company in the reports that it files or submits under the Exchange Act is accumulated and communicated to the companys management, including its principal executive
and principal financial officers, as appropriate to allow timely decisions regarding required disclosure. Management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of
achieving their objectives and management necessarily applies its judgment in evaluating the cost-benefit relationship of possible controls and procedures. Based on the evaluation of our disclosure controls and procedures as of June 30, 2008,
our chief executive officer and chief financial officer concluded that, as of such date, our disclosure controls and procedures were effective at the reasonable assurance level.

No change in our internal control over financial reporting (as defined in Rules 13a15(d) and 15d15(d) under the Exchange Act) occurred
during the fiscal quarter ended June 30, 2008 that has materially affected, or is reasonably likely to materially affect, our internal control over financial reporting.

PART II. OTHER INFORMATION



|ITEM 1A. | RISK FACTORS
|-------- | ------------

You should carefully
consider the risks described below in addition to the other information contained in this report, before making an investment decision. Our business, financial condition or results of operations could be harmed by any of these risks. The risks and
uncertainties described below are not the only ones we face. Additional risks not currently known to us or other factors not perceived by us to present significant risks to our business at this time also may impair our business operations.



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Risks Related to Our Business

We have a limited operating history and have incurred a cumulative loss since inception. If we do not generate significant revenues, we will not be profitable.

We have incurred significant losses since our inception in August 1998. At June 30, 2008, our accumulated deficit was approximately $165 million. We
have not generated any revenue from the sale of drug candidates to date. We expect that our annual operating losses will increase substantially over the next several years as we expand our research, development and commercialization efforts,
including as we:



| |  |  | complete the open-label extension phases of our phase II clinical trials for elvucitabine;
| | - |  | ------------------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1095 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete IND-enabling preclinical testing of ACH-1625 and begin clinical testing;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | complete our assessment of ACH-702 preclinical data and prepare for early clinical testing;
| | - |  | -------------------------------------------------------------------------------------------



| |  |  | advance our carbapenem compounds to identify a clinical lead candidate; and
| | - |  | ---------------------------------------------------------------------------



| |  |  | progress additional drug candidates.
| | - |  | ------------------------------------

To become profitable, we must successfully develop and obtain regulatory approval for our drug candidates and effectively manufacture, market and sell any drug candidates we develop. Accordingly, we may never generate significant revenues
and, even if we do generate significant revenues, we may never achieve profitability.

We will need substantial additional capital to fund our
operations, including drug candidate development, manufacturing and commercialization. If we do not have or cannot raise additional capital when needed, we will be unable to develop and commercialize our drug candidates successfully, and our ability
to operate as a going concern may be adversely affected.

We believe that our existing cash and cash equivalents will be sufficient to
support our current operating plan through at least the next twelve months. Our operating plan may change as a result of many factors, including:



| |  |  | the costs involved in the preclinical and clinical development, manufacturing and formulation of elvucitabine, ACH-1625 and ACH-702;
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the costs involved in the preclinical and clinical development of ACH-1095 and other NS4A antagonists, certain portions of which we share with Gilead Sciences;
| | - |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our ability to enter into corporate collaborations and the terms and success of these collaborations;
| | - |  | -----------------------------------------------------------------------------------------------------



| |  |  | the costs involved in obtaining regulatory approvals for our drug candidates;
| | - |  | -----------------------------------------------------------------------------



| |  |  | the scope, prioritization and number of programs we pursue;
| | - |  | -----------------------------------------------------------



| |  |  | the costs involved in preparing, filing, prosecuting, maintaining, enforcing and defending patent and other intellectual property claims;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our ability to raise incremental debt or equity capital;
| | - |  | --------------------------------------------------------



| |  |  | our ability to obtain stockholder approval for our August 2008 financing;
| | - |  | -------------------------------------------------------------------------



| |  |  | our acquisition and development of new technologies and drug candidates; and
| | - |  | ----------------------------------------------------------------------------



| |  |  | competing technological and market developments currently unknown to us.
| | - |  | ------------------------------------------------------------------------

If our operating plan changes, we may need additional funds sooner than planned. Such additional financing may not be available when we need it or may
not be available on terms that are favorable to us. In addition, we may seek additional capital due to favorable market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans. If
adequate funds are not available to us on a timely basis, or at all, we may be required to:



| |  |  | terminate or delay preclinical studies, clinical trials or other development activities for one or more of our drug candidates; or
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------



| |  |  | delay our establishment of sales and marketing capabilities or other activities that may be necessary to commercialize our drug candidates, if approved for sale.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------



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We may seek additional financing through a combination of private and public equity offerings, debt
financings and collaboration, strategic alliance and licensing arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, your ownership interest will be diluted, and the terms may include
adverse liquidation or other preferences that adversely affect your rights as a stockholder. For example, in August 2008, we issued shares of our common stock and warrants to purchase shares of common stock, resulting in gross proceeds to us of
$31.1 million. Debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions such as incurring additional debt, making capital expenditures or declaring dividends. If we
raise additional funds through collaboration, strategic alliance and licensing arrangements with third parties, we may have to relinquish valuable rights to our technologies or drug candidates, or grant licenses on terms that are not favorable to
us.

We depend on the success of our HCV drug candidates, ACH-1095 and ACH-1625, as well as elvucitabine, for the treatment of HIV infection, which are
all still under development.

We have invested a significant portion of our efforts and financial resources in the development of our
HCV candidates, ACH-1095 and ACH-1625, for the treatment of chronic hepatitis C, and elvucitabine for the treatment of HIV infection. Our ability to generate revenues will depend heavily on the successful development and commercialization of these
drug candidates. The development and commercial success of these drug candidates will depend on several factors, including the following:



| |  |  | our ability to enter into a corporate collaboration for the further development of elvucitabine and the terms and success of this collaboration;
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our ability to provide acceptable evidence of the safety and efficacy of these drug candidates in current and future clinical trials;
| | - |  | -------------------------------------------------------------------------------------------------------------------------------------



| |  |  | receipt of marketing approvals from the FDA and similar foreign regulatory authorities;
| | - |  | ---------------------------------------------------------------------------------------



| |  |  | establishing commercial manufacturing arrangements with third-party manufacturers;
| | - |  | ----------------------------------------------------------------------------------



| |  |  | launching commercial sales of the drugs, whether alone or in collaboration with others; and
| | - |  | -------------------------------------------------------------------------------------------



| |  |  | acceptance of the drug in the medical community and with third-party payors.
| | - |  | ----------------------------------------------------------------------------

We are currently studying elvucitabine in two open label extensions of recently completed phase II clinical trials. The longer-term results of these
phase II clinical trials may not be consistent with results observed in earlier phases of the trials, and even if positive, may not be necessarily indicative of the results we will obtain in phase III or other subsequent clinical trials that may be
required for regulatory approval of this drug candidate. If we are not successful in commercializing elvucitabine, or are significantly delayed in doing so, our business may be materially harmed.

We currently plan to enter into an alliance for the phase III development and commercialization of elvucitabine. Given the limited number of global
pharmaceutical companies which currently develop and market drugs for the treatment of HIV, and the strategic need for elvucitabine to be suitable for co-formulation with drugs already marketed or under development by a potential partner, the number
of potential partners is relatively small. Our partnering efforts to date have not yielded a satisfactory collaboration arrangement and we may not be successful in forming such an alliance. If we are not successful in forming an alliance before the
completion of the currently ongoing trial extensions, we do not plan to enter Phase III clinical trials and would not independently pursue further development or commercialization of elvucitabine.

We are currently studying our HCV candidates, ACH-1095 and ACH-1625, in preclinical studies and plan to enter human clinical trials for each in 2009.
Positive results in preclinical studies of a drug candidate may not be predictive of similar results in humans during clinical trials, and promising results from early clinical trials of a drug candidate may not be replicated in later clinical
trials. A number of companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in late-stage clinical trials even after achieving promising results in early-stage development. Accordingly, the results from the
completed preclinical studies for ACH-1095 and ACH-1625 may not be predictive of the results we may obtain in later stage trials. We do not expect any of our drug candidates to be commercially available for at least several years.



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Our market is subject to intense competition. If we are unable to compete effectively, our drug candidates may be
rendered noncompetitive or obsolete.

We are engaged in segments of the pharmaceutical industry that are highly competitive and rapidly
changing. Many large pharmaceutical and biotechnology companies, academic institutions, governmental agencies and other public and private research organizations are pursuing the development of novel drugs that target infectious diseases. We face,
and expect to continue to face, intense and increasing competition as new products enter the market and advanced technologies become available. In addition to currently approved drugs, there are a significant number of drugs that are currently under
development and may become available in the future for the treatment of HIV infection, chronic hepatitis C and serious hospital-based bacterial infections. We would expect elvucitabine, ACH-1095, ACH-1625 and ACH-702 to compete with the following
approved drugs and drug candidates currently under development:



| |  |  | Elvucitabine. If approved, elvucitabine would compete with the NRTIs currently marketed for treatment of HIV infection, including: Epivir (lamivudine),
Retrovir (AZT), Ziagen (abacavir), Combivir (lamivudine + AZT), Trizivir (lamivudine + AZT + abacavir) and Epzicom (lamivudine + abacavir) from GlaxoSmithKline, Hivid (ddC) from Hoffman-La Roche, Emtriva (FTC), Viread (tenofovir) and Truvada (FTC +
tenofovir) from Gilead Sciences and Videx EC, Videx (ddI) and Zerit (d4T) from Bristol-Myers Squibb. In addition, elvucitabine may compete with other NRTIs currently under development for HIV by companies such as Avexa, Medivir, Pharmasset and
Koronis. Other drugs in other classes recently approved for treatment of HIV infection include Selzentry (miraviroc, an entry inhibitor) from Pfizer and Isentress (raltegravir, an integrase inhibitor) from Merck. In addition, there are other classes
of drugs under development for the treatment of HIV infection by companies such as Abbott, Boehringer Ingelheim, Johnson & Johnson, Panacos, Roche, Schering-Plough, and Trimeris.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | ACH-1095 and ACH-1625. If approved, our NS4A antagonist, ACH-1095, and our protease inhibitor, ACH-1625, would compete with drugs currently approved for the
treatment of hepatitis C, the interferon-alpha based products from Roche (Pegasys and Roferon-A) or Schering-Plough (Intron-A or Peg-Intron) and the ribavirin based products from Schering-Plough (Rebetrol), Roche (Copegus) or generic versions sold
by various companies. In addition, our HCV compounds may compete with the interferon and ribavirin based drugs currently in development such as Valeants ribavirin analog (Viramidine) and Human Genome Sciences Albuferon. Other products
are also under development for the treatment of hepatitis C by companies such as Abbott, Anadys, Boehringer Ingelheim, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmithKline, Human Genome Sciences, Intermune, Johnson & Johnson, Medivir,
Merck, Novartis, Pfizer, Pharmasset, Roche, Schering-Plough, Valeant and Vertex.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | ACH-702. ACH-702, if approved, would compete with drugs currently marketed for the treatment of serious gram-positive nosocomial infections including:
vancomycin (multiple generic forms), Cubicin (daptomycin) by Cubist Pharmaceuticals, Zyvox (linezolid) by Pfizer and Synercid (dalfopristin + quinupristin) by King Pharmaceuticals. In addition, ACH-702 may compete with other drugs currently under
development for the treatment of nosocomial gram-positive infections including: dalbavancin in development by Pfizer, telavancin from Theravance, oritavancin by Intermune, doripenem by Johnson & Johnson, ceftobiprole by Basilea and
Johnson & Johnson, iclaprim by Arpida and garenoxacin by Schering-Plough. We may also compete with the following companies that have a strategic interest in the discovery, development and marketing of drugs for the treatment of bacterial
infections: Abbott, Aventis, Bristol-Myers Squibb, Cubist, GlaxoSmithKline, Merck, Novartis, Replidyne, Roche and Wyeth.
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Many of our competitors have:



| |  |  | significantly greater financial, technical and human resources than we have and may be better equipped to discover, develop, manufacture and commercialize drug
candidates;
| | - |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | more extensive experience in preclinical testing and clinical trials, obtaining regulatory approvals and manufacturing and marketing pharmaceutical products;
| | - |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | drug candidates that have been approved or are in late-stage clinical development; and/or
| | - |  | -----------------------------------------------------------------------------------------



| |  |  | collaborative arrangements in our target markets with leading companies and research institutions.
| | - |  | --------------------------------------------------------------------------------------------------



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Competitive products may render our products obsolete or noncompetitive before we can recover the
expenses of developing and commercializing our drug candidates. Furthermore, the development of new treatment methods and/or the widespread adoption or increased utilization of any vaccine for the diseases we are targeting could render our drug
candidates noncompetitive, obsolete or uneconomical. If we successfully develop and obtain approval for our drug candidates, we will face competition based on the safety and effectiveness of our drug candidates, the timing of their entry into the
market in relation to competitive products in development, the availability and cost of supply, marketing and sales capabilities, reimbursement coverage, price, patent position and other factors. If we successfully develop drug candidates but those
drug candidates do not achieve and maintain market acceptance, our business will not be successful.

We may grow through additional acquisitions, which
could dilute our existing shareholders and could involve substantial integration risks.

As part of our business strategy, we may
acquire other businesses and/or technologies in the future. We may issue equity securities as consideration for future acquisitions that would dilute our existing stockholders, perhaps significantly depending on the terms of the acquisition. We may
also incur additional debt in connection with future acquisitions, which, if available at all, may place additional restrictions on our ability to operate our business. Acquisitions may involve a number of risks, including:



| |  |  | difficulty in transitioning and integrating the operations and personnel of the acquired businesses, including different and complex accounting and financial
reporting systems;
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | potential disruption of our ongoing business and distraction of management;
| | - |  | ---------------------------------------------------------------------------



| |  |  | potential difficulty in successfully implementing, upgrading and deploying in a timely and effective manner new operational information systems and upgrades of our
finance, accounting and product distribution systems;
| | - |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | difficulty in incorporating acquired technology and rights into our products and technology;
| | - |  | --------------------------------------------------------------------------------------------



| |  |  | unanticipated expenses and delays in completing acquired development projects and technology integration;
| | - |  | ---------------------------------------------------------------------------------------------------------



| |  |  | management of geographically remote units both in the United States and internationally;
| | - |  | ----------------------------------------------------------------------------------------



| |  |  | impairment of relationships with partners;
| | - |  | ------------------------------------------



| |  |  | entering markets or types of businesses in which we have limited experience;
| | - |  | ----------------------------------------------------------------------------



| |  |  | potential loss of key employees of the acquired company; and
| | - |  | ------------------------------------------------------------



| |  |  | inaccurate assumptions of acquired companys product quality and/or product reliability.
| | - |  | ----------------------------------------------------------------------------------------

As a result of these and other risks, we may not realize anticipated benefits from any acquisitions. Any failure to achieve these benefits or failure to successfully
integrate acquired businesses and technologies could seriously harm our business.

If we are not able to attract and retain key management and
scientific personnel and advisors, we may not successfully develop our drug candidates or achieve our other business objectives.

We
depend upon our senior management and scientific staff for our business success. Key members of our senior team include Michael Kishbauch, our president and chief executive officer and Dr. Milind Deshpande, our executive vice president and
chief scientific officer. All of our employment agreements with our senior management employees are terminable without notice by the employee. The loss of the service of any of the key members of our senior management may significantly delay or
prevent the achievement of drug development and other business objectives. Our ability to attract and retain qualified personnel, consultants and advisors is critical to our success. We face intense competition for qualified individuals from
numerous pharmaceutical and biotechnology companies, universities, governmental entities and other research institutions. We may be unable to attract and retain these individuals, and our failure to do so would adversely affect our business.



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Our business has a substantial risk of product liability claims. If we are unable to obtain appropriate levels of
insurance, a product liability claim could adversely affect our business.

Our business exposes us to significant potential product
liability risks that are inherent in the development, manufacturing and sales and marketing of human therapeutic products. Although we do not currently commercialize any products, claims could be made against us based on the use of our drug
candidates in clinical trials. Product liability claims could delay or prevent completion of our clinical development programs. We currently have clinical trial insurance in an amount equal to up to $9.0 million in the aggregate and will seek to
obtain product liability insurance prior to the sales and marketing of any of our drug candidates. However, our insurance may not provide adequate coverage against potential liabilities. Furthermore, clinical trial and product liability insurance is
becoming increasingly expensive. As a result, we may be unable to maintain current amounts of insurance coverage or obtain additional or sufficient insurance at a reasonable cost to protect against losses that could have a material adverse effect on
us. If a claim is brought against us, we might be required to pay legal and other expenses to defend the claim, as well as uncovered damages awards resulting from a claim brought successfully against us. Furthermore, whether or not we are ultimately
successful in defending any such claims, we might be required to direct significant financial and managerial resources to such defense, and adverse publicity is likely to result.

Risks Related to the Development of Our Drug Candidates

All of our drug candidates are still in the early stages
of development and remain subject to clinical testing and regulatory approval. If we are unable to successfully develop and test our drug candidates, we will not be successful.

To date, we have not commercially marketed, distributed or sold any drug candidates. The success of our business depends primarily upon our ability to
develop and commercialize our drug candidates successfully. Our most advanced drug candidate is elvucitabine, which is currently in phase II clinical trials. Our other drug candidates are in various stages of preclinical development. Our drug
candidates must satisfy rigorous standards of safety and efficacy before they can be approved for sale. To satisfy these standards, we must engage in expensive and lengthy testing and obtain regulatory approval of our drug candidates. Despite our
efforts, our drug candidates may not:



| |  |  | offer therapeutic or other improvement over existing, comparable drugs;
| | - |  | -----------------------------------------------------------------------



| |  |  | be proven safe and effective in clinical trials;
| | - |  | ------------------------------------------------



| |  |  | have the desired effects or may include undesirable effects or the drug candidates may have other unexpected characteristics;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------



| |  |  | meet applicable regulatory standards;
| | - |  | -------------------------------------



| |  |  | be capable of being produced in commercial quantities at acceptable costs; or
| | - |  | -----------------------------------------------------------------------------



| |  |  | be successfully commercialized.
| | - |  | -------------------------------

In
addition, we may experience numerous unforeseen events during, or as a result of, preclinical testing and the clinical trial process that could delay or prevent our ability to receive regulatory approval or commercialize our drug candidates,
including:



| |  |  | regulators or Institutional Review Boards, or IRBs, may not authorize us to commence a clinical trial or conduct a clinical trial at a prospective trial site;
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | our pre-clinical tests or clinical trials may produce negative or inconclusive results, and we may decide, or regulators may require us, to conduct additional
pre-clinical testing or clinical trials, or we may abandon projects that we expect to be promising;
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | enrollment in our clinical trials may be slower than we currently anticipate or participants may drop out of our clinical trials at a higher rate than we currently
anticipate, resulting in significant delays;
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| |  |  | our third-party contractors may fail to comply with regulatory requirements or meet their contractual obligations to us in a timely manner;
| | - |  | -------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | we might have to suspend or terminate our clinical trials if the participants are being exposed to unacceptable health risks;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------



| |  |  | IRBs or regulators, including the FDA, may require that we hold, suspend or terminate clinical research for various reasons, including noncompliance with regulatory
requirements; and
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the supply or quality of our drug candidates or other materials necessary to conduct our clinical trials may be insufficient or inadequate.
| | - |  | -------------------------------------------------------------------------------------------------------------------------------------------

We, and a number of other companies in the pharmaceutical and biotechnology industries, have suffered significant
setbacks in later stage clinical trials even after achieving promising results in early-stage development. For example, in February 2007, we announced that we discontinued further clinical development of ACH-806 (also known as GS-9132) which was
determined to have positive antiviral effect in a proof-of-concept clinical trial in HCV infected patients, but also to elevate serum creatinine levels, a marker of kidney function. There can be no assurance that we have identified the source of the
serum creatinine elevation and that we will not see a similar outcome in human clinical trials with that programs successor compound, ACH-1095. Accordingly, there can be no assurance that this, or another type of toxicity, will not arise in
future clinical trials. Additionally, the results from the completed preclinical studies and clinical trials and ongoing clinical trials for elvucitabine, ACH-702, ACH-1625 and our other drug candidates may not be predictive of the results we may
obtain in later stage trials. In addition, we have not yet made a final determination regarding the most appropriate therapeutic application or clinical plan for ACH-702, and we may not be successful in developing a clinical plan that is acceptable
to the FDA or that ultimately demonstrates ACH-702 to be safe, tolerable and efficacious. We do not expect any of our drug candidates to be commercially available for at least several years.

If we are unable to obtain U.S. and/or foreign regulatory approval, we will be unable to commercialize our drug candidates.

Our drug candidates are subject to extensive governmental regulations relating to among other things, research, testing, development, manufacturing,
safety, efficacy, record keeping, labeling, marketing and distribution of drugs. Rigorous preclinical testing and clinical trials and an extensive regulatory approval process are required in the United States and in many foreign jurisdictions prior
to the commercial sale of our drug candidates. Satisfaction of these and other regulatory requirements is costly, time consuming, uncertain and subject to unanticipated delays. It is possible that none of the drug candidates we are developing will
obtain marketing approval. In connection with the clinical trials for elvucitabine, ACH-1095, ACH-702, ACH-1625 and any other drug candidate we may seek to develop in the future, we face risks that:



| |  |  | the drug candidate may not prove to be efficacious;
| | - |  | ---------------------------------------------------



| |  |  | the drug may not prove to be safe;
| | - |  | ----------------------------------



| |  |  | the results may not confirm the positive results from earlier preclinical studies or clinical trials; and
| | - |  | ---------------------------------------------------------------------------------------------------------



| |  |  | the results may not meet the level of statistical significance required by the FDA or other regulatory agencies.
| | - |  | ----------------------------------------------------------------------------------------------------------------

We have limited experience in conducting and managing the clinical trials necessary to obtain regulatory approvals, including approval by the FDA. The
time required to complete clinical trials and for FDA and other countries regulatory review processes is uncertain and typically takes many years. Our analysis of data obtained from preclinical and clinical activities is subject to
confirmation and interpretation by regulatory authorities, which could delay, limit or prevent regulatory approval. We may also encounter unanticipated delays or increased costs due to government regulation from future legislation or administrative
action or changes in FDA policy during the period of product development, clinical trials and FDA regulatory review.

Any delay in
obtaining or failure to obtain required approvals could materially adversely affect our ability to progress the development of a drug candidate and to generate revenues from that drug candidate. In particular, we have scheduled a pre-IND development
meeting with the FDA during the third quarter to hold discussions on the most appropriate



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clinical strategy for ACH-702 and follow with submission of an IND to the FDA, if appropriate, based upon the outcome of those discussions. Given the
complexity of the mechanism of action of this compound, which operates via a three-part target including gyrase, topoisomerase IV and primase, the complexity of the preclinical results noted with ACH-702, and the evolving regulatory climate for
antibacterials, we believe our development strategy for this compound should be discussed with the FDA before initiating human clinical studies. There can be no assurance that the FDA will approve our IND application once filed. Furthermore, any
regulatory approval to market a product may be subject to limitations on the indicated uses for which we may market the product and affect reimbursement by third-party payors. These limitations may limit the size of the market for the product. We
are also subject to numerous foreign regulatory requirements governing the conduct of clinical trials, manufacturing and marketing authorization, pricing and third-party reimbursement. The foreign regulatory approval process includes all of the
risks associated with FDA approval described above as well as risks attributable to the satisfaction of foreign regulations. Approval by the FDA does not ensure approval by regulatory authorities outside the United States. Foreign jurisdictions may
have different approval procedures than those required by the FDA and may impose additional testing requirements for our drug candidates.

If clinical
trials for our drug candidates are prolonged or delayed, we may be unable to commercialize our drug candidates on a timely basis, which would require us to incur additional costs and delay our receipt of any product revenue.

We cannot predict whether we will encounter problems with any of our completed, ongoing or planned clinical trials that will cause us or regulatory
authorities to delay, suspend or terminate clinical trials, or delay the analysis of data from our completed or ongoing clinical trials. Any of the following could delay the clinical development of our drug candidates:



| |  |  | ongoing discussions with the FDA or comparable foreign authorities regarding the scope or design of our clinical trials;
| | - |  | ------------------------------------------------------------------------------------------------------------------------



| |  |  | delays in receiving, or the inability to obtain, required approvals from institutional review boards or other reviewing entities at clinical sites selected for
participation in our clinical trials;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | delays in enrolling volunteers and patients into clinical trials;
| | - |  | -----------------------------------------------------------------



| |  |  | a lower than anticipated retention rate of volunteers and patients in clinical trials;
| | - |  | --------------------------------------------------------------------------------------



| |  |  | the need to repeat clinical trials as a result of inconclusive or negative results or unforeseen complications in testing;
| | - |  | --------------------------------------------------------------------------------------------------------------------------



| |  |  | inadequate supply or deficient quality of drug candidate materials or other materials necessary to conduct our clinical trials;
| | - |  | -------------------------------------------------------------------------------------------------------------------------------



| |  |  | unfavorable FDA inspection and review of a clinical trial site or records of any clinical or preclinical investigation;
| | - |  | -----------------------------------------------------------------------------------------------------------------------



| |  |  | serious and unexpected drug-related side effects experienced by participants in our clinical trials; or
| | - |  | -------------------------------------------------------------------------------------------------------



| |  |  | the placement by the FDA of a clinical hold on a trial.
| | - |  | -------------------------------------------------------

Our ability to enroll patients in our clinical trials in sufficient numbers and on a timely basis will be subject to a number of factors, including the size of the patient population, the nature of the protocol, the
proximity of patients to clinical sites, the availability of effective treatments for the relevant disease and the eligibility criteria for the clinical trial. Delays in patient enrollment may result in increased costs and longer development times.
For example, we experienced delays in patient enrollment in connection with our phase II trial of elvucitabine in HIV infected patients who have failed a HAART regimen which included Epivir (lamivudine) due to the strict entry criteria for this
trial. As a result, we expanded the number of sites at which the trial was conducted and changed the protocol of the trial to include additional treatment with elvucitabine after the initial 14 days of treatment. In addition, subjects may drop out
of our clinical trials, and thereby impair the validity or statistical significance of the trials.

We, the FDA or other applicable
regulatory authorities or IRBs may suspend clinical trials of a drug candidate at any time if we or they believe the subjects or patients participating in such clinical trials are being exposed to unacceptable health risks or for other reasons.



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We cannot predict whether any of our drug candidates will encounter problems during clinical trials which
will cause us or regulatory authorities to delay or suspend these trials, or which will delay the analysis of data from these trials. In addition, it is impossible to predict whether legislative changes will be enacted, or whether FDA regulations,
guidance or interpretations will be changed, or what the impact of such changes, if any, may be. If we experience any such problems, we may not have the financial resources to continue development of the drug candidate that is affected or the
development of any of our other drug candidates.

In addition, we, along with our collaborators or subcontractors, may not employ, in any
capacity, persons who have been debarred under the FDAs Application Integrity Policy. Employment of such a debarred person (even if inadvertently) may result in delays in FDAs review or approval of our products, or the rejection of data
developed with the involvement of such persons.

Even if we obtain regulatory approvals, our drug candidates will be subject to ongoing regulatory
review. If we fail to comply with continuing U.S. and applicable foreign regulations, we could lose those approvals, and our business would be seriously harmed.

Even if we receive regulatory approval of any drugs we are developing or may develop, we will be subject to continuing regulatory review, including the review of clinical results which are reported after our drug
candidates become commercially available approved drugs. As greater numbers of patients use a drug following its approval, side effects and other problems may be observed after approval that were not seen or anticipated during pre-approval clinical
trials. In addition, the manufacturer, and the manufacturing facilities we use to make any approved drugs, will also be subject to periodic review and inspection by the FDA. The subsequent discovery of previously unknown problems with the drug,
manufacturer or facility may result in restrictions on the drug, manufacturer or facility, including withdrawal of the drug from the market. If we fail to comply with applicable continuing regulatory requirements, we may be subject to fines,
suspension or withdrawal of regulatory approval, product recalls and seizures, operating restrictions and criminal prosecutions.

Our
product promotion and advertising is also subject to regulatory requirements and continuing regulatory review. In particular, the marketing claims we will be permitted to make in labeling or advertising regarding our marketed products will be
limited by the terms and conditions of the FDA-approved labeling. We must submit copies of our advertisements and promotional labeling to the FDA at the time of initial publication or dissemination. If the FDA believes these materials or statements
promote our products for unapproved indications, or with unsubstantiated claims, or if we fail to provide appropriate safety-related information, the FDA could allege that our promotional activities misbrand our products. Specifically, the FDA could
issue an untitled letter or warning letter, which may demand, among other things, that we cease such promotional activities and issue corrective advertisements and labeling. The FDA also could take enforcement action including seizure of allegedly
misbranded product, injunction or criminal prosecution against us and our officers or employees. If we repeatedly or deliberately fail to submit such advertisements and labeling to the agency, the FDA could withdraw our approvals. Moreover, the
Department of Justice can bring civil or criminal actions against companies that promote drugs or biologics for unapproved uses, based on the False Claims Act and other federal laws governing reimbursement for such products under the Medicare,
Medicaid and other federally supported healthcare programs. Monetary penalties in such cases have often been substantial, and civil penalties can include costly mandatory compliance programs and exclusion from federal healthcare programs.

If we do not comply with laws regulating the protection of the environment and health and human safety, our business could be adversely affected.

Our research and development efforts involve the controlled use of hazardous materials, chemicals and various radioactive compounds.
Although we believe that our safety procedures for the use, manufacture, storage, handling and disposing of these materials comply with the standards prescribed by federal, state and local laws and regulations, the risk of accidental contamination
or injury from these materials cannot be eliminated. If an accident occurs, we could be held liable for resulting damages, which could be substantial. We are also subject to numerous environmental, health and workplace safety laws and regulations,
including those governing laboratory procedures, exposure to blood-borne pathogens and the handling of biohazardous materials. Additional federal, state and local laws and regulations affecting our operations may be adopted in the future. Although
we maintain workers compensation insurance to cover us for costs we may incur due to injuries to our employees resulting from the use of these materials, this insurance may not provide adequate coverage against potential liabilities. Due to
the small amount of hazardous materials that we generate, we have determined that the cost to secure insurance coverage for environmental liability and toxic tort claims far exceeds the benefits. Accordingly, we do not



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maintain any insurance to cover pollution conditions or other extraordinary or unanticipated events relating to our use and disposal of hazardous materials.
We may incur substantial costs to comply with, and substantial fines or penalties if we violate, any of these laws or regulations.

Risks Related to
Commercialization of Our Drug Candidates

If we are unable to establish sales and marketing capabilities or enter into agreements with third parties
to market and sell our drug candidates, we may not generate product revenue.

We have no commercial products, and we do not currently
have an organization for the sales and marketing of pharmaceutical products. In order to successfully commercialize any drugs that may be approved in the future by the FDA or comparable foreign regulatory authorities, we must build our sales and
marketing capabilities or make arrangements with third parties to perform these services. For certain drug candidates in selected indications where we believe that an approved product could be commercialized by a specialty sales force in North
America that calls on a limited but focused group of physicians, we intend to commercialize these products ourselves. However, in therapeutic indications that require a large sales force selling to a large and diverse prescribing population and for
markets outside of North America, we plan to enter into arrangements with other companies for commercialization. For example, we have entered into an agreement with Gilead Sciences for the development and commercialization of certain of our HCV
candidates involving NS4A antagonism. If we are unable to establish adequate sales, marketing and distribution capabilities, whether independently or with third parties, we may not be able to generate product revenue and may not become profitable.

If physicians and patients do not accept our future drugs, we may be unable to generate significant revenue, if any.

Even if elvucitabine, ACH-1095, ACH-702, ACH-1625 or any other drug candidates we may develop or acquire in the future, obtain regulatory approval, they
may not gain market acceptance among physicians, health care payors, patients and the medical community. Factors that we believe could materially affect market acceptance of our product candidates include:



| |  |  | the timing of market introduction of competitive drugs;
| | - |  | -------------------------------------------------------



| |  |  | the demonstrated clinical safety and efficacy of our product candidates compared to other drugs;
| | - |  | ------------------------------------------------------------------------------------------------



| |  |  | the cost-effectiveness of our product candidates;
| | - |  | -------------------------------------------------



| |  |  | the availability of reimbursement from managed care plans and other third-party payors;
| | - |  | ---------------------------------------------------------------------------------------



| |  |  | the convenience and ease of administration of our product candidates;
| | - |  | ---------------------------------------------------------------------



| |  |  | the existence, prevalence and severity of adverse side effects;
| | - |  | ---------------------------------------------------------------



| |  |  | other potential advantages of alternative treatment methods; and
| | - |  | ----------------------------------------------------------------



| |  |  | the effectiveness marketing and distribution support.
| | - |  | -----------------------------------------------------

If our approved drugs fail to achieve market acceptance, we would not be able to generate significant revenue.

If
third-party payors do not adequately reimburse patients for any of our drug candidates that are approved for marketing, they might not be purchased or used, and our revenues and profits will not develop or increase.

Our revenues and profits will depend significantly upon the availability of adequate reimbursement for the use of any approved drug candidates from
governmental and other third-party payors, both in the United States and in foreign markets. Reimbursement by a third party may depend upon a number of factors, including the third-party payors determination that use of a product is:



| |  |  | a covered benefit under its health plan;
| | - |  | ----------------------------------------



| |  |  | safe, effective and medically necessary;
| | - |  | ----------------------------------------



| |  |  | appropriate for the specific patient;
| | - |  | -------------------------------------



| |  |  | cost effective; and
| | - |  | -------------------



| |  |  | neither experimental nor investigational.
| | - |  | -----------------------------------------



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Obtaining reimbursement approval for a product from each third-party and government payor is a
time-consuming and costly process that could require us to provide supporting scientific, clinical and cost-effectiveness data for the use of any approved drugs to each payor. We may not be able to provide data sufficient to gain acceptance with
respect to reimbursement. There also exists substantial uncertainty concerning third-party reimbursement for the use of any drug candidate incorporating new technology, and even if determined eligible, coverage may be more limited than the purposes
for which the drug is approved by the FDA. Moreover, eligibility for coverage does not imply that any drug will be reimbursed in all cases or at a rate that allows us to make a profit or even cover our costs. Interim payments for new products, if
applicable, may also not be sufficient to cover our costs and may not be made permanent. Reimbursement rates may vary according to the use of the drug and the clinical setting in which it is used, may be based on payments allowed for lower-cost
products that are already reimbursed, may be incorporated into existing payments for other products or services, and may reflect budgetary constraints and/or imperfections in Medicare or Medicaid data used to calculate these rates. Net prices for
products may be reduced by mandatory discounts or rebates required by government health care programs or by any future relaxation of laws that restrict imports of certain medical products from countries where they may be sold at lower prices than in
the United States.

There have been, and we expect that there will continue to be, federal and state proposals to constrain expenditures
for medical products and services, which may affect payments for any of our approved products. The Centers for Medicare and Medicaid Services frequently change product descriptors, coverage policies, product and service codes, payment methodologies
and reimbursement values. Third-party payors often follow Medicare coverage policy and payment limitations in setting their own reimbursement rates and may have sufficient market power to demand significant price reductions. As a result of actions
by these third-party payors, the health care industry is experiencing a trend toward containing or reducing costs through various means, including lowering reimbursement rates, limiting therapeutic class coverage and negotiating reduced payment
schedules with service providers for drug products.

Our inability to promptly obtain coverage and profitable reimbursement rates from
government-funded and private payors for any approved products could have a material adverse effect on our operating results and our overall financial condition.

Federal legislation has increased the pressure to reduce prices of pharmaceutical products paid for by Medicare, which could adversely affect our revenues, if any.

The Medicare Prescription Drug Improvement and Modernization Act of 2003, or MMA, changes the way Medicare covers and pays for pharmaceutical products.
The legislation expanded Medicare coverage for drug purchases by the elderly and eventually will introduce a new reimbursement methodology based on average sales prices for drugs. In addition, this legislation provides authority for limiting the
number of drugs that will be covered in any therapeutic class. As a result of this legislation and the expansion of federal coverage of drug products, we expect that there will be additional pressure to contain and reduce costs. These cost reduction
initiatives and other provisions of this legislation could decrease the coverage and price that we receive for any approved products and could seriously harm our business. While the MMA applies only to drug benefits for Medicare beneficiaries,
private payors often follow Medicare coverage policy and payment limitations in setting their own reimbursement rates, and any reduction in reimbursement that results from the MMA may result in a similar reduction in payments from private payors.

Risks Related to Our Dependence on Third Parties

We may not be able to execute our business strategy if we are unable to enter into alliances with other companies that can provide capabilities and funds for the development and commercialization of our drug candidates. If we are
unsuccessful in forming or maintaining these alliances on favorable terms, our business may not succeed.

We have entered into a
collaboration arrangement with Gilead Sciences for the development and commercialization of certain of our HCV compounds involving NS4A antagonism, and we may enter into additional collaborative arrangements in the future. For example, we plan to
enter into an alliance for the phase III development and commercialization of elvucitabine, our drug candidate for treatment of HIV. Given the limited number of global pharmaceutical companies which currently develop and market drugs for the
treatment of HIV, and the strategic need for elvucitabine to be suitable for co-formulation with drugs already marketed or under development by a potential partner, the number of potential partners is relatively small. We have had difficulty forming
such an alliance to date, and we may not be successful in forming such an alliance. If we are not successful in forming an alliance, we will not independently pursue further development and



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commercialization of elvucitabine. We also may enter into alliances with major biotechnology or pharmaceutical companies to jointly develop other specific
drug candidates and to jointly commercialize them if they are approved. In such alliances, we would expect our biotechnology or pharmaceutical collaborators to provide substantial funding, as well as significant capabilities in clinical development,
regulatory affairs, marketing and sales. We may not be successful in entering into any such alliances on favorable terms, if at all. Even if we do succeed in securing such alliances, we may not be able to maintain them if, for example, development
or approval of a drug candidate is delayed or sales of an approved drug are disappointing. Furthermore, any delay in entering into collaboration agreements could delay the development and commercialization of our drug candidates and reduce their
competitiveness even if they reach the market. Any such delay related to our collaborations could adversely affect our business.

If a collaborative
partner terminates or fails to perform its obligations under agreements with us, the development and commercialization of our drug candidates could be delayed or terminated.

If Gilead Sciences or another, future collaborative partner does not devote sufficient time and resources to collaboration arrangements with us, we may
not realize the potential commercial benefits of the arrangement, and our results of operations may be adversely affected. In addition, if any existing or future collaboration partner were to breach or terminate its arrangements with us, the
development and commercialization of the affected drug candidate could be delayed, curtailed or terminated because we may not have sufficient financial resources or capabilities to continue development and commercialization of the drug candidate on
our own. Under our collaboration agreement with Gilead Sciences, Gilead Sciences may terminate the collaboration for any reason at any time upon 120 days notice. If Gilead Sciences were to exercise this right, the development and commercialization
of our HCV compounds would be adversely affected.

Much of the potential revenue from our existing and future collaborations will consist
of contingent payments, such as payments for achieving development milestones and royalties payable on sales of drugs developed. The milestone and royalty revenues that we may receive under these collaborations will depend upon our
collaborators ability to successfully develop, introduce, market and sell new products. In addition, our collaborators may decide to enter into arrangements with third parties to commercialize products developed under our existing or future
collaborations using our technologies, which could reduce the milestone and royalty revenue that we may receive, if any. In many cases we will not be involved in these processes and accordingly will depend entirely on our collaborators. Our
collaboration partners may fail to develop or effectively commercialize products using our products or technologies because they:



| |  |  | decide not to devote the necessary resources due to internal constraints, such as limited personnel with the requisite scientific expertise, limited cash resources
or specialized equipment limitations, or the belief that other drug development programs may have a higher likelihood of obtaining regulatory approval or may potentially generate a greater return on investment;
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | do not have sufficient resources necessary to carry the drug candidate through clinical development, regulatory approval and commercialization; or
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | cannot obtain the necessary regulatory approvals.
| | - |  | -------------------------------------------------

In addition, a collaborator may decide to pursue a competitive drug candidate developed outside of the collaboration. In particular, Gilead Sciences, our collaborator for our chronic hepatitis C program, currently is
developing other products for the treatment of chronic hepatitis C, and the results of its development efforts could affect its commitment to our drug candidate. If a collaboration partner fails to develop or effectively commercialize drug
candidates or drugs for any of these reasons, we may not be able to replace the collaboration partner with another partner to develop and commercialize a drug candidate or drugs under the terms of the collaboration. We may also be unable to obtain,
on terms acceptable to us, a license from such collaboration partner to any of its intellectual property that may be necessary or useful for us to continue to develop and commercialize a drug candidate.

We rely on third parties to conduct our clinical trials, and those third parties may not perform satisfactorily, including failing to meet established deadlines for
the completion of such trials.

We do not have the ability to independently conduct clinical trials for our drug candidates, and we
rely on third parties such as contract research organizations, medical institutions and clinical investigators to enroll qualified patients and conduct our clinical trials. Our reliance on these third parties for clinical development activities
reduces our control over



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these activities. Accordingly, these third-party contractors may not complete activities on schedule, or may not conduct our clinical trials in accordance
with regulatory requirements or our trial design. To date, we believe our contract research organizations and other similar entities with which we are working have performed well. However, if these third parties do not successfully carry out their
contractual duties or meet expected deadlines, we may be required to replace them. Although we believe that there are a number of other third-party contractors we could engage to continue these activities, it may result in a delay of the affected
trial. Accordingly, our efforts to obtain regulatory approvals for and commercialize our drug candidates may be delayed.

We currently depend on
third-party manufacturers to produce our preclinical and clinical drug supplies and intend to rely upon third-party manufacturers to produce commercial supplies of any approved drug candidates. If in the future we manufacture any of our drug
candidates, we will be required to incur significant costs and devote significant efforts to establish and maintain these capabilities.

We rely upon third parties to produce material for preclinical and clinical testing purposes and intend to continue to do so in the future. We also expect to rely upon third parties to produce materials required for the commercial
production of our drug candidates if we succeed in obtaining necessary regulatory approvals. If we are unable to arrange for third-party manufacturing, or to do so on commercially reasonable terms, we may not be able to complete development of our
drug candidates or market them. Reliance on third-party manufacturers entails risks to which we would not be subject if we manufactured drug candidates ourselves, including reliance on the third party for regulatory compliance and quality assurance,
the possibility of breach of the manufacturing agreement by the third party because of factors beyond our control and the possibility of termination or nonrenewal of the agreement by the third party, based on its own business priorities, at a time
that is costly or damaging to us. In addition, the FDA and other regulatory authorities require that our drug candidates be manufactured according to current good manufacturing practice regulations. Any failure by us or our third-party manufacturers
to comply with current good manufacturing practices and/or our failure to scale up our manufacturing processes could lead to a delay in, or failure to obtain, regulatory approval of any of our drug candidates. In addition, such failure could be the
basis for action by the FDA to withdraw approvals for drug candidates previously granted to us and for other regulatory action.

We
currently rely on a single manufacturer for the preclinical and clinical supplies of each of our drug candidates and do not currently have relationships for redundant supply or a second source for any of our drug candidates. To date, our third-party
manufacturers have met our manufacturing requirements, but we cannot be assured that they will continue to do so. Any performance failure on the part of our existing or future manufacturers could delay clinical development or regulatory approval of
our drug candidates or commercialization of any approved products. If for some reason our current contract manufacturers cannot perform as agreed, we may be required to replace them. Although we believe there are a number of potential replacements
as our manufacturing processes are not manufacturer specific, we may incur added costs and delays in identifying and qualifying any such replacements. Furthermore, although we generally do not begin a clinical trial unless we believe we have a
sufficient supply of a drug candidate to complete the trial, any significant delay in the supply of a drug candidate for an ongoing trial due to the need to replace a third-party manufacturer could delay completion of the trial.

We may in the future elect to manufacture certain of our drug candidates in our own manufacturing facilities. If we do so, we will require substantial
additional funds and need to recruit qualified personnel in order to build or lease and operate any manufacturing facilities.

Risks Related to Patents
and Licenses

If we are unable to adequately protect our drug candidates, or if we infringe the rights of others, our ability to successfully
commercialize our drug candidates will be harmed.

As of June 30, 2008, our patent portfolio included a total of 308 patents and
patent applications worldwide. We own or hold exclusive licenses to a total of 12 U.S. issued patents and 25 U.S. pending patent applications, as well as 250 pending PCT applications and foreign counterparts to many of these patents and patent
applications. Our success depends in part on our ability to obtain patent protection both in the United States and in other countries for our drug candidates. Our ability to protect our drug candidates from unauthorized or infringing use by third
parties depends in substantial part on our ability to obtain and maintain valid and enforceable patents. Due to evolving legal standards relating to the patentability, validity and enforceability of patents covering pharmaceutical inventions and the
scope of claims made under these patents, our ability to maintain, obtain and enforce patents is uncertain and involves complex legal and factual questions. Accordingly, rights under any issued patents may not provide us with sufficient protection
for our drug candidates or provide sufficient protection to



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afford us a commercial advantage against competitive products or processes. In addition, we cannot guarantee that any patents will issue from any pending or
future patent applications owned by or licensed to us. Even if patents have issued or will issue, we cannot guarantee that the claims of these patents are or will be valid or enforceable or will provide us with any significant protection against
competitive products or otherwise be commercially valuable to us. Patent applications in the United States are maintained in confidence for up to 18 months after their filing. In some cases, however, patent applications remain confidential in the
U.S. Patent and Trademark Office, which we refer to as the U.S. Patent Office, for the entire time prior to issuance as a U.S. patent. Similarly, publication of discoveries in the scientific or patent literature often lag behind actual discoveries.
Consequently, we cannot be certain that we or our licensors or co-owners were the first to invent, or the first to file patent applications on, our drug candidates or their use as anti-infective drugs. In the event that a third party has also filed
a U.S. patent application relating to our drug candidates or a similar invention, we may have to participate in interference proceedings declared by the U.S. Patent Office to determine priority of invention in the United States. The costs of these
proceedings could be substantial and it is possible that our efforts would be unsuccessful, resulting in a loss of our U.S. patent position. Furthermore, we may not have identified all U.S. and foreign patents or published applications that affect
our business either by blocking our ability to commercialize our drugs or by covering similar technologies that affect our drug market.

The laws of some foreign jurisdictions do not protect intellectual property rights to the same extent as in the United States and many companies have encountered significant difficulties in protecting and defending such rights in foreign
jurisdictions. If we encounter such difficulties in protecting or are otherwise precluded from effectively protecting our intellectual property rights in foreign jurisdictions, our business prospects could be substantially harmed.

We license patent rights from third-party owners. If such owners do not properly maintain or enforce the patents underlying such licenses, our competitive position
and business prospects will be harmed.

We are party to a number of licenses that give us rights to third-party intellectual property
that is necessary or useful for our business. In particular, we have obtained a sublicense from Vion Pharmaceuticals and a license from Emory University with respect to elvucitabine. We also recently obtained an exclusive worldwide license for
research, development and commercialization of certain compounds for the treatment of serious bacterial infections from FOB Synthesis, Inc. We may enter into additional licenses for third-party intellectual property in the future. Our success will
depend in part on the ability of our licensors to obtain, maintain and enforce patent protection for their intellectual property, in particular, those patents to which we have secured exclusive rights. Our licensors may not successfully prosecute
the patent applications to which we are licensed. Even if patents issue in respect of these patent applications, our licensors may fail to maintain these patents, may determine not to pursue litigation against other companies that are infringing
these patents, or may pursue such litigation less aggressively than we would. In addition, our licensors may terminate their agreements with us in the event we breach the applicable license agreement and fail to cure the breach within a specified
period of time. Without protection for the intellectual property we license, other companies might be able to offer substantially identical products for sale, which could adversely affect our competitive business position and harm our business
prospects.

Litigation regarding patents, patent applications and other proprietary rights may be expensive and time consuming. If we are involved in
such litigation, it could cause delays in bringing drug candidates to market and harm our ability to operate.

Our success will depend
in part on our ability to operate without infringing the proprietary rights of third parties. Although we are not currently aware of any litigation or other proceedings or third-party claims of intellectual property infringement related to our drug
candidates, the pharmaceutical industry is characterized by extensive litigation regarding patents and other intellectual property rights. Other parties may obtain patents in the future and allege that the use of our technologies infringes these
patent claims or that we are employing their proprietary technology without authorization. Likewise, third parties may challenge or infringe upon our existing or future patents. Under our license agreements with Vion Pharmaceuticals we have the
right, but not an obligation, to bring actions against an infringing third party. If we do not bring an action within a specified number of days, the licensor may bring an action against the infringing party. Pursuant to our license agreement with
Emory University and our research collaboration and license agreement with Gilead Sciences, Emory and Gilead Sciences have the primary right, but not an obligation, to bring actions against an infringing third party. However, if Gilead Sciences or
Emory elects not to bring an action, we may bring an action against the infringing party.

Proceedings involving our patents or patent applications or
those of others could result in adverse decisions regarding:



| |  |  | the patentability of our inventions relating to our drug candidates; and/or
| | - |  | ---------------------------------------------------------------------------



| |  |  | the enforceability, validity or scope of protection offered by our patents relating to our drug candidates.
| | - |  | -----------------------------------------------------------------------------------------------------------



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Even if we are successful in these proceedings, we may incur substantial costs and divert management time
and attention in pursuing these proceedings, which could have a material adverse effect on us. If we are unable to avoid infringing the patent rights of others, we may be required to seek a license, defend an infringement action or challenge the
validity of the patents in court. Patent litigation is costly and time consuming. We may not have sufficient resources to bring these actions to a successful conclusion. In addition, if we do not obtain a license, develop or obtain non-infringing
technology, fail to defend an infringement action successfully or have infringed patents declared invalid, we may:



| |  |  | incur substantial monetary damages;
| | - |  | -----------------------------------



| |  |  | encounter significant delays in bringing our drug candidates to market; and/or
| | - |  | ------------------------------------------------------------------------------



| |  |  | be precluded from participating in the manufacture, use or sale of our drug candidates or methods of treatment requiring licenses.
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------

Confidentiality agreements with employees and others may not adequately prevent disclosure of trade secrets and other proprietary information and may not adequately
protect our intellectual property.

We rely on trade secrets to protect our technology, especially where we do not believe patent
protection is appropriate or obtainable. However, trade secrets are difficult to protect. In order to protect our proprietary technology and processes, we also rely in part on confidentiality and intellectual property assignment agreements with our
corporate partners, employees, consultants, outside scientific collaborators and sponsored researchers and other advisors. These agreements may not effectively prevent disclosure of confidential information nor result in the effective assignment to
us of intellectual property, and may not provide an adequate remedy in the event of unauthorized disclosure of confidential information or other breaches of the agreements. In addition, others may independently discover our trade secrets and
proprietary information, and in such case we could not assert any trade secret rights against such party. Enforcing a claim that a party illegally obtained and is using our trade secrets is difficult, expensive and time consuming, and the outcome is
unpredictable. In addition, courts outside the United States may be less willing to protect trade secrets. Costly and time-consuming litigation could be necessary to seek to enforce and determine the scope of our proprietary rights, and failure to
obtain or maintain trade secret protection could adversely affect our competitive business position.

Risks Relating to Our Common Stock

Our stock price is likely to be volatile, and the market price of our common stock may decline in value in the future.

The market price of our common stock has fluctuated in the past and is likely to fluctuate in the future. During the period from January 1, 2007 to
June 30, 2008, our stock price has ranged from a low of $2.10 to a high of $19.61. Market prices for securities of early stage pharmaceutical, biotechnology and other life sciences companies have historically been particularly volatile. Some of
the factors that may cause the market price of our common stock to fluctuate include:



| |  |  | the results of our currently on-going phase II trial extensions and any future clinical trials for elvucitabine;
| | - |  | ----------------------------------------------------------------------------------------------------------------



| |  |  | the results of ongoing preclinical studies and planned clinical trials of our preclinical drug candidates, including ACH-702, ACH-1095 and ACH-1625;
| | - |  | ----------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the entry into, or termination of, key agreements, in particular our collaboration agreement with Gilead Sciences or our sublicense agreement with Vion
Pharmaceuticals, or any new collaboration agreement we may enter for elvucitabine;
| | - |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the results of regulatory reviews relating to the approval of our drug candidates;
| | - |  | ----------------------------------------------------------------------------------



| |  |  | the initiation of, material developments in, or conclusion of litigation to enforce or defend any of our intellectual property rights;
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------



| |  |  | failure of any of our drug candidates, if approved, to achieve commercial success;
| | - |  | ----------------------------------------------------------------------------------



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| |  |  | general and industry-specific economic conditions that may affect our research and development expenditures;
| | - |  | ------------------------------------------------------------------------------------------------------------



| |  |  | the results of clinical trials conducted by others on drugs that would compete with our drug candidates;
| | - |  | --------------------------------------------------------------------------------------------------------



| |  |  | the failure or discontinuation of any of our research programs;
| | - |  | ---------------------------------------------------------------



| |  |  | issues in manufacturing our drug candidates or any approved products;
| | - |  | ---------------------------------------------------------------------



| |  |  | the introduction of technological innovations or new commercial products by us or our competitors;
| | - |  | --------------------------------------------------------------------------------------------------



| |  |  | changes in estimates or recommendations by securities analysts, if any, who cover our common stock;
| | - |  | ---------------------------------------------------------------------------------------------------



| |  |  | future sales of our common stock;
| | - |  | ---------------------------------



| |  |  | changes in the structure of health care payment systems;
| | - |  | --------------------------------------------------------



| |  |  | period-to-period fluctuations in our financial results; and
| | - |  | -----------------------------------------------------------



| |  |  | low trading volume of our common stock.
| | - |  | ---------------------------------------

In addition, if we fail to reach an important research, development or commercialization milestone or result by a publicly expected deadline, even if by only a small margin, there could be significant impact on the market price of our
common stock. Additionally, as we approach the announcement of important clinical data or other significant information and as we announce such results and information, we expect the price of our common stock to be particularly volatile, and
negative results would have a substantial negative impact on the price of our common stock.

The stock markets in general have experienced
substantial volatility that has often been unrelated to the operating performance of individual companies. These broad market fluctuations may adversely affect the trading price of our common stock.

In the past, following periods of volatility in the market price of a companys securities, stockholders have often instituted class action
securities litigation against those companies. Such litigation, if instituted, could result in substantial costs and diversion of management attention and resources, which could significantly harm our business operations and reputation.

Our executive officers, directors and principal stockholders own a large percentage of our voting common stock and could limit our stockholders influence on
corporate decisions or could delay or prevent a change in corporate control.

As of August 13, 2008, our directors, executive officers
and current holders of more than 5% of our outstanding common stock, together with their affiliates and related persons, beneficially own, in the aggregate, approximately 69% of our outstanding common stock. As a result, these stockholders, if
acting together, have the ability to determine the outcome of all matters submitted to our stockholders for approval, including the election and removal of directors and any merger, consolidation or sale of all or substantially all of our assets and
other extraordinary transactions. The interests of this group of stockholders may not always coincide with our corporate interests or the interest of other stockholders, and they may act in a manner with which you may not agree or that may not be in
the best interests of other stockholders. This concentration of ownership may have the effect of:



| |  |  | delaying, deferring or preventing a change in control of our company;
| | - |  | ---------------------------------------------------------------------



| |  |  | entrenching our management and/or board;
| | - |  | ----------------------------------------



| |  |  | impeding a merger, consolidation, takeover or other business combination involving our company; or
| | - |  | --------------------------------------------------------------------------------------------------



| |  |  | discouraging a potential acquirer from making a tender offer or otherwise attempting to obtain control of our company.
| | - |  | ----------------------------------------------------------------------------------------------------------------------

Our management is required to devote substantial time and incur additional expense to comply with public company regulations. Our failure to comply with such
regulations could subject us to public investigations, fines, enforcement actions and other sanctions by regulatory agencies and authorities and, as a result, our stock price could decline in value.



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As a private company with limited resources, we maintained a small finance and accounting staff. As a
public company, the Sarbanes-Oxley Act of 2002 and the related rules and regulations of the SEC, as well as the rules of the Nasdaq Global Market, have required us to implement additional corporate governance practices and adhere to a variety of
reporting requirements and complex accounting rules. Compliance with these public company obligations places significant additional demands on our finance and accounting staff and on our financial, accounting and information systems.

In particular, as a public company, our management is required to conduct an annual evaluation of our internal controls over financial reporting and
include a report of management on our internal controls in our annual reports on Form 10-K. If we are unable to continue to conclude that we have effective internal controls over financial reporting or, if our independent auditors are unable to
provide us with an attestation and an unqualified report as to the effectiveness of our internal controls over financial reporting, investors could lose confidence in the reliability of our financial statements, which could result in a decrease in
the value of our common stock.

We do not anticipate paying cash dividends, and accordingly stockholders must rely on stock appreciation for any return
on their investment in us.

We anticipate that we will retain our earnings, if any, for future growth and therefore do not anticipate
paying cash dividends in the future. As a result, only appreciation of the price of our common stock will provide a return to stockholders.



|ITEM 4. | SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS
|------- | ---------------------------------------------------

We held our annual meeting of stockholders on June 3, 2008. At the meeting, each of Michael Grey, Michael Kishbauch and Robert Van Nostrand was re-elected as a class II director for a three-year term to expire in 2011. As of
April 18, 2008, the record date for the meeting, 15,640,406 shares of common stock were outstanding. A quorum consisting of 11,910,946 shares of common stock were present or represented at the meeting. The additional directors whose term of
office continued after the meeting are Jason Fisherman, Jean-Francois Formela, Gary Frashier, James Garvey, David Wright and David Scheer. In addition, the stockholders ratified the selection of PricewaterhouseCoopers, LLP to serve as our
independent registered public accounting firm for the fiscal year ending December 31, 2008. The number of votes cast for and against or withheld with respect to each matter voted upon at the meeting and the number of abstentions are as follows:



|                                           |  |               |  |               |  |              |  |                |  |                
|------------------------------------------ |  | ------------- |  | ------------- |  | ------------ |  | -------------- |  | ---------------
|Nominee                                    |  | Votes inFavor |  | VotesWithheld |  | VotesAgainst |  | VotesAbstained |  | BrokerNon-Votes
|Election of Directors:                     |  |               |  |               |  |              |  |                |  |                
|Michael Grey                               |  | 9,322,569     |  | 2,588,377     |  |             |  |               |  |               
|                                           |  |               |  |               | 
|Michael Kishbauch                          |  | 10,704,879    |  | 1,206,067     |  |             |  |               |  |               
|                                           |  |               |  |               | 
|Robert Van Nostrand                        |  | 11,580,366    |  | 330,580       |  |             |  |               |  |               
|                                           |  |               |  |               | 
|Ratification of PricewaterhouseCoopers LLP |  | 11,910,946    |  |              |  |             |  |               |  |               



|ITEM 6. | EXHIBITS
|------- | --------



|31.1 | Certification of President and Chief Executive Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(a) promulgated under the Securities Exchange Act of 1934, as
amended.
|---- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



|31.2 | Certification of Chief Financial Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(a) promulgated under the Securities Exchange Act of 1934, as amended.
|---- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------



|32.1 | Certification of President and Chief Executive Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(b) promulgated under the Securities Exchange Act of 1934, as
amended, and Section 1350 of Chapter 63 of Title 18 of the United States Code.
|---- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



|32.2 | Certification of Chief Financial Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(b) promulgated under the Securities Exchange Act of 1934, as amended, and
Section 1350 of Chapter 63 of Title 18 of the United States Code.
|---- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned, thereunto duly authorized.



|                      |  |  |  |                                             
|--------------------- |  |  |  | --------------------------------------------
|                      |  |  |  | ACHILLION PHARMACEUTICALS, INC.             
|                      |  | 
|Date: August 14, 2008 |  |  |  | /s/ Michael D. Kishbauch                    
|                      |  |  |  | President and Chief Executive Officer       
|                      |  |  |  | (Principal Executive Officer)               
|                      |  | 
|Date: August 14, 2008 |  |  |  | /s/ Mary Kay Fenton                         
|                      |  |  |  | Chief Financial Officer                     
|                      |  |  |  | (Principal Financial and Accounting Officer)



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EXHIBIT INDEX



|            |  |                                                                                                                                                                                                                                                              
|----------- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Exhibit No. |  | Exhibit                                                                                                                                                                                                                                                      
|31.1        |  | Certification of President and Chief Executive Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(a) promulgated under the Securities Exchange Act of 1934, as amended.                                                                      
|            | 
|31.2        |  | Certification of Chief Financial Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(a) promulgated under the Securities Exchange Act of 1934, as amended.                                                                                    
|            | 
|32.1        |  | Certification of President and Chief Executive Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(b) promulgated under the Securities Exchange Act of 1934, as amended,
and Section 1350 of Chapter 63 of Title 18 of the United States Code.
|            | 
|32.2        |  | Certification of Chief Financial Officer of Achillion Pharmaceuticals, Inc. pursuant to Rule 13a-14(b) promulgated under the Securities Exchange Act of 1934, as amended, and
Section 1350 of Chapter 63 of Title 18 of the United States Code.              



42