EXECUTION COPY










                                                                   EXHIBIT 10.64

                          OPTIMER PHARMACEUTICALS, INC.



                   SERIES C PREFERRED STOCK PURCHASE AGREEMENT



                            CLOSING: APRIL ___, 2005




<PAGE>


                                TABLE OF CONTENTS


                                                                            PAGE
                                                                            ----

1.       AUTHORIZATION AND SALE OF PREFERRED SHARES............................1

         1.1      AUTHORIZATION................................................1
         1.2      SALE OF SERIES C PREFERRED STOCK.............................1

2.       CLOSING; DELIVERY.....................................................1

         2.1      CLOSING......................................................1
         2.2      DELIVERY.....................................................1

3.       REPRESENTATIONS AND WARRANTIES OF THE COMPANY.........................2

         3.1      ORGANIZATION AND STANDING; CERTIFICATE AND BY-LAWS...........2
         3.2      CORPORATE POWER..............................................2
         3.3      CAPITALIZATION...............................................2
         3.4      SUBSIDIARIES.................................................3
         3.5      AUTHORIZATION................................................3
         3.6      OUTSTANDING INDEBTEDNESS.....................................3
         3.7      TITLE TO PROPERTIES AND ASSETS...............................3
         3.8      PATENTS, TRADEMARKS..........................................4
         3.9      COMPLIANCE WITH OTHER INSTRUMENTS; NONE BURDENSOME...........4
         3.10     LITIGATION...................................................4
         3.11     TAX RETURNS..................................................5
         3.12     EMPLOYEES; CONSULTANTS.......................................5
         3.13     REGISTRATION RIGHTS..........................................5
         3.14     GOVERNMENTAL CONSENTS........................................5
         3.15     SECURITIES LAW EXEMPTION.....................................5
         3.16     AGREEMENTS; ACTION...........................................6
         3.17     BROKERS OR FINDERS; OTHER OFFERS.............................6
         3.18     DISCLOSURE...................................................6
         3.19     LICENSES.....................................................6
         3.20     CERTAIN ACTIONS..............................................6
         3.21     FINANCIAL STATEMENTS.........................................7
         3.22     CHANGES......................................................7
         3.23     REAL PROPERTY HOLDING COMPANY................................8
         3.24     INVESTMENT COMPANY...........................................8
         3.25     MINUTES......................................................8
         3.26     HOLDING COMPANY STATUS.......................................8
         3.27     ACCOUNTING...................................................8
         3.28     SECTION 1202 COMPLIANCE......................................8
         3.29     SECTION 83(B) ELECTIONS......................................9
         3.30     MATERIAL LIABILITIES.........................................9
         3.31     RELATED-PARTY TRANSACTIONS...................................9
         3.32     STOCK CERTIFICATES..........................................10

                                      -i-
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                               TABLE OF CONTENTS
                                  (CONTINUED)
                                                                            PAGE
                                                                            ----

4.       REPRESENTATIONS AND WARRANTIES OF THE INVESTORS......................10

         4.1      AUTHORIZATION...............................................10
         4.2      EXPERIENCED ACCREDITED INVESTOR.............................10
         4.3      INVESTMENT..................................................10
         4.4      RESTRICTED SECURITIES.......................................10
         4.5      FURTHER LIMITATIONS ON DISPOSITION..........................11
         4.6      NO PUBLIC MARKET............................................11
         4.7      ACCESS TO DATA..............................................11
         4.8      BROKERS OR FINDERS..........................................11

5.       CONDITIONS OF INVESTORS' OBLIGATIONS AT THE CLOSING..................12

         5.1      REPRESENTATIONS AND WARRANTIES TRUE.........................12
         5.2      COVENANTS...................................................12
         5.3      CONSENTS....................................................12
         5.4      OPINION OF THE COMPANY'S COUNSEL............................12
         5.5      COMPLIANCE CERTIFICATE......................................12
         5.6      CERTIFICATE OF INCORPORATION................................12
         5.7      ANCILLARY AGREEMENTS........................................12
         5.8      PROCEEDINGS AND DOCUMENTS...................................12
         5.9      RESERVATION OF CONVERSION STOCK.............................12
         5.10     COMPLIANCE WITH LAWS........................................12
         5.11     BOARD OF DIRECTORS..........................................13
         5.12     APPROVAL BY THE BOARD OF DIRECTORS OF PAR PHARMACEUTICAL....13
         5.13     MANAGEMENT RIGHTS LETTER....................................13
         5.14     SECURING OF ADDITIONAL FUNDING..............................13

6.       CONDITIONS TO COMPANY'S OBLIGATIONS AT THE CLOSING...................13

         6.1      REPRESENTATIONS AND WARRANTIES TRUE.........................13
         6.2      CONSENTS....................................................13
         6.3      CERTIFICATE OF INCORPORATION................................13
         6.4      ANCILLARY AGREEMENTS........................................13
         6.5      COMPLIANCE WITH ALL LAWS....................................13

7.       MISCELLANEOUS........................................................14

         7.1      GOVERNING LAW...............................................14
         7.2      SURVIVAL....................................................14
         7.3      FINDER'S FEE................................................14
         7.4      SUCCESSORS AND ASSIGNS......................................14
         7.5      ENTIRE AGREEMENT............................................14
         7.6      SEVERABILITY................................................14
         7.7      AMENDMENT AND WAIVER........................................14
         7.8      DELAYS OR OMISSIONS.........................................15

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                               TABLE OF CONTENTS
                                  (CONTINUED)
                                                                            PAGE
                                                                            ----
         7.9      NOTICES.....................................................15
         7.10     EXPENSES....................................................15
         7.11     TITLES AND SUBTITLES........................................15
         7.12     COUNTERPARTS................................................15
         7.13     INDEMNIFICATION.............................................15

                                     -iii-

<PAGE>


                                    EXHIBITS

Exhibit A      Schedule of Investors
Exhibit B      Amended and Restated Certificate of Incorporation
Exhibit C      Amended and Restated Investors' Rights Agreement
Exhibit D      Amended and Restated Co-Sale Agreement
Exhibit E      Amended and Restated Voting Agreement
Exhibit F      Schedule of Exceptions
Exhibit G      Opinion of Wilson Sonsini Goodrich & Rosati, P.C.

                                      -iv-

<PAGE>

                          OPTIMER PHARMACEUTICALS, INC.

                   SERIES C PREFERRED STOCK PURCHASE AGREEMENT

     This Series C Preferred Stock Purchase  Agreement (the "AGREEMENT") is made
as of April ___,  2005 by and among  Optimer  Pharmaceuticals,  Inc., a Delaware
corporation  (the  "COMPANY"),  and the  investors  listed  on the  Schedule  of
Investors attached as EXHIBIT A (the "INVESTORS").

1.        AUTHORIZATION AND SALE OF PREFERRED SHARES.

          1.1  AUTHORIZATION.  The Company has  authorized  (a) the issuance and
sale pursuant to this Agreement of up to an aggregate of 3,333,333 shares of its
Series C  Preferred  Stock  (the  "SHARES")  having  the  rights,  restrictions,
privileges and  preferences set forth in the Company's  Restated  Certificate of
Incorporation  attached as EXHIBIT B (the "RESTATED  CERTIFICATE");  and (b) the
reservation of shares of Common Stock for issuance upon conversion of the Shares
(the  "CONVERSION  STOCK").  The  Company  shall  adopt  and file  the  Restated
Certificate  with the  Secretary  of State of the State of Delaware on or before
the Closing (as defined below).

          1.2  SALE OF  SERIES C  PREFERRED  STOCK.  Subject  to the  terms  and
conditions  hereof,  the Company will issue and sell to the Investors,  and each
Investor will purchase  from the Company,  severally and not jointly,  the total
number of shares of Series C Preferred Stock specified  opposite such Investor's
name on the Schedule of Investors  for the purchase  price of $3.60 per share at
the Closing (as defined  hereafter).  The Company's agreement with each Investor
is a separate  agreement,  and the issuance of the Shares to each  Investor is a
separate sale and issuance.

2.        CLOSING; DELIVERY.

          2.1 CLOSING.  The sale, purchase and issuance of the Shares under this
Agreement shall take place at one closing (the "CLOSING").  The Closing shall be
held at 3 p.m. on April ___, 2005 (the "CLOSING DATE"), at the offices of Wilson
Sonsini  Goodrich  & Rosati,  P.C.,  650 Page Mill Road,  Palo Alto,  California
94304, or at such other time and place as the Company and Investors representing
a majority of the Shares to be sold in the Closing may agree.

          2.2  DELIVERY.  At the  Closing,  subject to the terms and  conditions
hereof,  the  Company  shall  duly  execute  and  deliver  to  each  Investor  a
certificate,  in due and proper form,  representing  the Shares purchased by the
Investor from the Company  against  payment of the purchase  price  therefore by
check,  wire  transfer  of  immediately  available  funds,  or  cancellation  of
indebtedness.  Each Investor shall also enter into (i) that certain  Amended and
Restated   Investors'  Rights  Agreement  dated  as  of  the  date  hereof  (the
"INVESTORS' RIGHTS AGREEMENT"),  by and among the Company and the Investors, the
form of which is  attached  hereto as EXHIBIT C, (ii) that  certain  Amended and
Restated Co-Sale Agreement date as of the date hereof (the "CO-SALE AGREEMENT"),
by and among the  Company,  the  Investors  and the Founders (as defined in such
agreement),  the form of which is  attached  hereto as EXHIBIT D, and (iii) that
certain Amended and Restated  Voting  Agreement dated as of the date hereof (the
"VOTING Agreement"),  by and among the Company, the Investors,  and the Founders
(as defined in the Voting  Agreement),  the form of which is attached  hereto as

<PAGE>

EXHIBIT  E. The  Investors'  Rights  Agreement,  Co-Sale  Agreement,  and Voting
Agreement are collectively referred to as the "ANCILLARY AGREEMENTS".

     3.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY. Except as otherwise set
forth on the Schedule of  Exceptions  attached  hereto as Exhibit F, the Company
represents and warrants to the Investors as of the Closing as follows:

          3.1 ORGANIZATION AND STANDING; CERTIFICATE AND BY-LAWS. The Company is
a corporation duly organized,  validly existing,  and in good standing under the
laws of the State of Delaware. The Company has all requisite corporate power and
authority  to own and  operate  its  properties  and  assets and to carry on its
business as presently conducted and as proposed to be conducted.  The Company is
qualified to do business as a foreign  corporation  in the State of  California.
The Company is not so qualified in any other  jurisdiction and the failure to be
so qualified will not have a material  adverse effect on the Company's  business
as now conducted or as proposed to be  conducted.  The Company has furnished the
Investors  with copies of its  Certificate  of  Incorporation  and Bylaws.  Said
copies are true,  correct and  complete and contain all  amendments  through the
Closing Date.

          3.2 CORPORATE POWER. The Company has all requisite legal and corporate
power to  execute  and  deliver  this  Agreement,  to sell and issue the  Shares
hereunder,  to issue the  Conversion  Stock,  and to carry out and  perform  its
obligations under the terms of this Agreement and the Ancillary Agreements.

          3.3  CAPITALIZATION.

               (a) The  authorized  capital  stock of the  Company  consists  of
55,000,000  shares of Common Stock,  $0.001 par value, and 31,000,000  shares of
Preferred  Stock,  $0.001 par value,  of which (i)  5,000,000  shares  have been
designated Series A Preferred Stock, (ii) 14,000,000 shares have been designated
Series B Preferred Stock,  (iii) 3,500,000 shares have been designated  Series C
Preferred  Stock,  and (iv)  8,500,000  shares  have  been  designated  Series D
Preferred Stock. Immediately prior to the Closing,  3,400,000 shares of Series A
Preferred  Stock,  8,954,431  shares of Series B Preferred  Stock,  no shares of
Series C Preferred  Stock,  and no shares of Series D Preferred Stock are issued
and outstanding.

               (b) Immediately prior to the Closing,  5,082,711 shares of Common
Stock are issued and  outstanding.  All  issued  and  outstanding  shares of the
Company's  capital stock are duly authorized and validly issued,  fully paid and
nonassessable,  and were issued in compliance with applicable  federal and state
securities laws.

               (c) Except for (i) the  conversion  privileges  of the  Preferred
Stock,  (ii) 4,000,000 shares of Common Stock reserved for issuance  pursuant to
the  Company's  1998 Stock Plan,  as amended,  as of the Closing,  and (iii) the
rights  provided  in  the  Investors'  Rights  Agreement,  there  are  no  other
outstanding  shares of capital  stock or  outstanding  rights of first  refusal,
preemptive  rights or other rights,  options,  warrants,  conversion  rights, or
other  agreements  either directly or indirectly for the purchase or acquisition
from the  Company  or for the  voting of any shares of its  capital  stock.  The

                                      -2-
<PAGE>

rights,  privileges and  preferences  of each series of Preferred  Stock are set
forth in the Restated Certificate.

          3.4  SUBSIDIARIES.  The  Company  has no  subsidiaries  or  affiliated
companies  and does not otherwise own or control,  directly or  indirectly,  any
equity interest in any corporation, association or business entity.

          3.5  AUTHORIZATION.  All corporate  action on the part of the Company,
its officers,  directors and stockholders  necessary for (a) the  authorization,
execution,  delivery and  performance  by the Company of this  Agreement and the
Ancillary Agreements, (b) the authorization,  issuance, sale and delivery of the
Shares and the Conversion Stock, and (c) the performance of all of the Company's
obligations hereunder has been taken or will be taken prior to the Closing. This
Agreement  and the  Ancillary  Agreements,  when  executed and  delivered by the
Company,  shall constitute valid and legally binding  obligations of the Company
enforceable in accordance with their respective terms,  except (i) as limited by
laws of general application relating to bankruptcy, insolvency and the relief of
debtors,  (ii) as  limited  by  rules  of law  governing  specific  performance,
injunctive  relief or other  equitable  remedies  and by general  principles  of
equity, and (iii) to the extent the indemnification  provisions contained in the
Investor  Rights'  Agreement  may  further  be limited  by  applicable  laws and
principles of public  policy.  The Shares,  when issued in  compliance  with the
provisions of this Agreement,  will be duly authorized and validly issued, fully
paid and nonassessable, will be issued in compliance with applicable federal and
state  securities  laws,  and will have the rights,  preferences  and privileges
described in the Restated  Certificate;  and the Shares and the Conversion Stock
will be free of any  liens or  encumbrances,  assuming  the  Investors  take the
Shares and the Conversion Stock with no notice thereof,  other than any liens or
encumbrances created by or imposed upon the Investors;  PROVIDED,  HOWEVER, that
the Shares and the Conversion  Stock may be subject to  restrictions on transfer
under applicable securities laws as set forth herein. The Shares are not subject
to any preemptive rights, rights of first refusal or similar rights.

          3.6  OUTSTANDING  INDEBTEDNESS.  The Company has no  indebtedness  for
borrowed money which the Company has directly or indirectly  created,  incurred,
assumed or guaranteed,  or with respect to which the Company has become directly
or indirectly  liable.  The Company has no liability or obligation,  absolute or
contingent,  other than liabilities or obligations of less than $25,000 each and
in the aggregate less than $50,000, under purchase orders, sales contracts, real
property leases,  equipment leases or similar  obligations,  all incurred in the
ordinary course of business. For purposes of this Section 3.6, all indebtedness,
liabilities,  agreements,  understandings,  instruments,  contracts and proposed
transactions  involving the same person or entity (including persons or entities
the Company has reason to believe are affiliated  therewith) shall be aggregated
for the purpose of meeting the aforementioned individual minimum dollar amounts.

          3.7  TITLE  TO  PROPERTIES  AND  ASSETS.  The  Company  has  good  and
marketable  title to its  properties  and assets,  and has good title to all its
leasehold interests,  in each case subject to no mortgage,  pledge, lien, lease,
loan,  encumbrance  or charge,  except (i) the lien of current taxes not yet due
and  payable,  and (ii)  possible  minor  liens and  encumbrances  (of which the
Company has no knowledge)  which do not in any case materially  detract from the
value of the  property  subject  thereto  or  materially  impair  the  Company's

                                      -3-
<PAGE>

operations,  and which have not arisen  otherwise than in the ordinary course of
business.  With respect to property it leases, the Company is in compliance with
such leases in all material respects.

          3.8  PATENTS, TRADEMARKS.  To the Company's knowledge, the Company has
sufficient title and ownership of all patents,  patent  applications,  licenses,
trademarks,  service marks,  trade names,  inventions,  franchises,  copyrights,
trade  secrets,  information  and other  proprietary  rights  necessary  for the
operation  of its  business as now  conducted  and as  proposed to be  conducted
(collectively  the  "INTELLECTUAL  PROPERTY") with no known  infringement of the
rights of others. There are no outstanding options,  licenses,  or agreements of
any kind related to the foregoing, nor is the Company bound by or a party to any
options,   licenses  or   agreements   with  respect  to  the  patents,   patent
applications,  licenses,  trade marks,  service marks, trade names,  inventions,
franchises,  copyrights,  trade  secrets,  information,  proprietary  rights  or
processes  of any other  person or entity.  The  Company  has not  received  any
communications  alleging  that the Company has violated,  or by  conducting  its
business as  proposed,  would  violate any of the patents,  trademarks,  service
marks, trade names, copyrights, trade secrets or other proprietary rights of any
other person or entity. The Company, after reasonable inquiry, is not aware that
any of its employees or consultants is obligated  under any contract  (including
licenses, covenants or commitments of any nature) or other agreement, or subject
to any judgment,  decree or order of any court or  administrative  agency,  that
would  interfere  with the use of the  employee's  best  efforts to promote  the
interests of the Company or that would  conflict with the Company's  business as
proposed to be conducted.  Neither the execution nor delivery of this Agreement,
nor the operation of the Company's  business by the employees or  consultants of
the  Company,  nor the  conduct of the  Company's  business  as  proposed,  will
conflict with or result in a breach of the terms, conditions or provisions of or
constitute a default under, any contract, covenant or instrument under which any
of such employees or consultants is now obligated.

          3.9 COMPLIANCE WITH OTHER INSTRUMENTS; NONE BURDENSOME. The Company is
not in violation of any term of its Certificate of  Incorporation  or Bylaws or,
in any  material  respect,  any  contract,  agreement,  mortgage,  indebtedness,
indenture,   instrument,  judgment,  decree,  order  or  any  statute,  rule  or
regulation applicable to the Company. The execution,  delivery,  and performance
of and  compliance  with  this  Agreement,  the  Ancillary  Agreements  and  the
consummation  of the  transactions  contemplated  hereby and  thereby,  have not
resulted and will not result in any such  violation,  or be in conflict  with or
constitute a default under any such term, or result in the creation of any lien,
mortgage,  pledge, encumbrance or charge upon any of the properties or assets of
the Company;  and there is no such  violation  or default  which  materially  or
adversely affects the Company's business or any of its properties or assets. The
Company is not a party to any  contract,  agreement or  instrument or subject to
any judgment, order, injunction, rule or regulation which, in the opinion of the
Company,  materially and adversely affects its business,  operations,  financial
condition or prospects.

          3.10  LITIGATION.   There  are  no  actions,  suits,   proceedings  or
investigations  pending against the Company or any of its properties  before any
court or governmental  agency (nor, to the best of the Company's  knowledge,  is
there any reasonable basis therefor or threat thereof).  The foregoing includes,
without  limitation,  actions pending or threatened (or any basis therefor known

                                      -4-
<PAGE>

to the Company after reasonable  inquiry)  involving the prior employment of any
of the Company's  employees or former employees or their  obligations  under any
agreements  with prior  employers.  The Company is not a party or subject to the
provisions of any order, writ,  injunction,  judgment, or decree of any court or
governmental agency or instrumentality. There is no action, suit, proceeding, or
investigation  by the Company  currently  pending or that the Company intends to
initiate.

          3.11 TAX RETURNS. The Company has filed or obtained extensions for all
federal, state and other tax returns which are required to be filed and has paid
all taxes which have become due and  payable.  The Company has not been  advised
that any of its returns, federal, state or other, have been or are being audited
as of the date thereof.

          3.12  EMPLOYEES;  CONSULTANTS.  To the Company's  knowledge  after due
inquiry, no employee or consultant of the Company is in violation of any term of
any employment or consulting contract,  patent disclosure  agreement,  invention
assignment  agreement,  proprietary  information  agreement or other contract or
agreement  relating to the  relationship of such employee or consultant with the
Company or any other party because of the nature of the business conducted or to
be  conducted  by the  Company.  The  Company  does not have any  employment  or
consulting contracts,  deferred compensation  agreements or bonus,  incentive or
profit sharing plans,  either  currently in effect or proposed,  except the 1998
Stock Plan adopted by the  Company's  Board of Directors and  shareholders.  The
Company has no collective  bargaining  agreements  with any of its employees and
there is no labor union  organizing  activity pending or threatened with respect
to the  Company.  All  employees  of  the  Company  have  signed  a  Proprietary
Information  Agreement and all consultants of the Company have signed Consulting
Agreements  in  substantially  the forms  furnished  to  special  counsel to the
Investors.

          3.13 REGISTRATION RIGHTS.  Except as provided in the Investors' Rights
Agreement,  the Company is not under any contractual  obligation to register any
of its  presently  outstanding  securities  or any of its  securities  which may
hereafter be issued.

          3.14 GOVERNMENTAL  CONSENTS. No consent,  approval or authorization of
or  designation,  declaration or filing with any  governmental  authority on the
part of the Company is  required  in  connection  with the valid  execution  and
delivery of this  Agreement,  the  Ancillary  Agreements  or the offer,  sale or
issuance of the Shares (and the Conversion  Stock),  or the  consummation of any
other transaction  contemplated hereby, except qualification or registration (or
taking such action as may be necessary to secure an exemption from qualification
or  registration,  if available)  of the offer,  sale and issuance of the Shares
(and the Conversion  Stock) under  applicable  Blue Sky laws,  which filings and
qualifications, if required, will be accomplished in a timely manner.

          3.15  SECURITIES  LAW  EXEMPTION.  Subject  to  the  accuracy  of  the
Investors'  representations in Section 4 of this Agreement,  the offer, sale and
issuance  of the Shares and the  issuance  of the  Conversion  Stock  constitute
transactions exempt from the registration and prospectus  delivery  requirements
of the Securities Act of 1933, as amended (the "ACT"),  and have been registered
or  qualified  (or are exempt from  registration  and  qualification)  under the
registration,  permit or  qualification  requirements  of all  applicable  state
securities laws.

                                      -5-
<PAGE>

          3.16 AGREEMENTS; ACTION. Except for agreements explicitly contemplated
hereby, there are no agreements, understandings or proposed transactions between
the  Company  and  any  of  its  officers,  employees,  consultants,  directors,
affiliates,  or any  affiliate  thereof.  The  Company  and,  to  the  Company's
knowledge after having made due inquiry, its officers employees, consultants and
directors,  have no interest (other than as holders of less than 1% of any class
of securities of a publicly-traded  company),  either directly or indirectly, in
any entity, including without limitation thereto, any corporation,  partnership,
joint venture, proprietorship,  firm, licensee, business or association (whether
as an employee, officer, director,  shareholder,  agent, independent contractor,
security holder, creditor,  consultant or otherwise) that presently (i) provides
any services or designs, produces and/or sells any products or product lines, or
engages  or plans to engage in any  activity  which is the same,  similar  to or
competitive with any activity or business in which the Company is now engaged or
plans to engage;  (ii) is a  supplier,  customer,  creditor,  or has an existing
contractual  relationship  with any of its managing  employees  or  consultants;
(iii) has any direct or  indirect  interest  in any asset or  property,  real or
personal,  tangible,  or  intangible,  of the Company or any  property,  real or
personal, tangible or intangible, that is necessary or desirable for the conduct
of its current or presently proposed business.

               (a)  The  Schedule  of  Exceptions  sets  forth a list of all (i)
contracts, indentures, agreements or licenses of any patent, copyright, or other
proprietary  agreement  to which the Company is a party and which  relate to the
payment  or  receipt  of money  in  excess  of  $25,000,  (ii)  all  consulting,
employment and severance  agreements,  (iii) all distribution,  reseller,  joint
venture and corporate partnering  agreements and (iv) all leases which relate to
the payment of money in excess of $50,000 (each a "MATERIAL CONTRACT").

          3.17  BROKERS OR FINDERS; OTHER OFFERS.  The Company has not incurred,
and will not incur,  directly or indirectly,  as a result of any action taken by
or on behalf of the Company,  any  liability  for  brokerage or finders' fees or
agents' commissions or any similar charges in connection with this Agreement.

          3.18  DISCLOSURE.  Neither this Agreement or the Ancillary  Agreements
nor any  information  in the  Exhibits  hereto  or  otherwise  furnished  to the
Investors  taken as a whole  contains any untrue  statement  of a material  fact
regarding  the Company or omits to state a material  fact  necessary in order to
make the statements  contained  herein and therein not misleading  regarding the
Company.

          3.19 LICENSES.  The Company has all licenses and permits  necessary to
the conduct of its  business  as  currently  being  conducted  (federal,  state,
foreign and local),  the failure to obtain  which would have a material  adverse
effect on the Company's business  properties,  and such licenses and permits are
in full force and effect.

          3.20  CERTAIN  ACTIONS.  The Company has not (i)  declared or paid any
dividends,  or authorized or made any  distribution  upon or with respect to any
class or series of its  capital  stock,  (ii) made any loans or  advances to any
person,  other than loans in connection  with employee  relocations and ordinary
advances for travel expenses, (iii) sold, exchanged or otherwise disposed of any
of its assets or rights  other than in the  ordinary  course of business or (iv)
redeemed  or  obligated  itself to redeem any of its capital  stock,  other than

                                      -6-
<PAGE>

repurchases  of unvested  shares of Common Stock from  terminated  employees and
consultants  at a repurchase  price equal to the  original  issue price for such
repurchased  shares.  (a) The  Company is not a party to and is not bound by any
contract,  agreement,  or instrument,  or subject to any restrictions  under its
Certificate of Incorporation or Bylaws,  which materially and adversely  affects
its  business  as now  conducted  and  as now  proposed  to be  conducted.

          3.21 FINANCIAL STATEMENTS.  The Company has delivered to the Investors
the Company's unaudited financial statements as of December 31, 2004 ("FINANCIAL
STATEMENTS").  The  Financial  Statements,  (i) are  complete and correct in all
material respects,  (ii) are in accordance with the Company's books and records,
(iii) fairly  present its financial  position as of the dates  indicated and the
results of its operations for the periods  indicated and (iv) have been prepared
in  conformity  with  generally  accepted  accounting  principles   consistently
applied, except that unaudited Financial Statements do not include footnotes and
do not  reflect  normal  year-end  adjustments  (which  are not  expected  to be
material).  Except as set forth in the Financial Statements,  the Company has no
material  liabilities  or  obligations,  absolute or  contingent,  except  those
incurred in the ordinary course of business since December 31, 2004,  which have
not  been in the  aggregate  materially  adverse.  Except  as  disclosed  in the
Financial  Statements,  the  Company is not a  guarantor  or  indemnitor  of any
indebtedness  of any other person,  firm or  corporation.

          3.22 CHANGES. Since December 31, 2004 there has not been:

               (a)  any  waiver  by the  Company  of a  valuable  right  or of a
material debt owed to it;

               (b)  any   satisfaction  or  discharge  of  any  lien,  claim  or
encumbrance or payment of any obligation by the Company,  except in the ordinary
course  of  business  and  which  is not  material  to the  assets,  properties,
financial  condition,  operating  results or  business  of the  Company (as such
business is presently conducted and as it is now proposed to be conducted);

               (c) any change or amendment to a material contract or arrangement
by which the Company or any of its assets or properties is bound or subject;

               (d) any change in any compensation  arrangement or agreement with
any executive officer;

               (e) any change in the assets, liabilities, financial condition or
operations  of the Company,  except  changes in the ordinary  course of business
which have not been, either in any case or in the aggregate, materially adverse;

               (f) any change, except in the ordinary course of business, in the
contingent  obligations  of  the  Company  by  way  of  guaranty,   endorsement,
indemnity, warranty or otherwise;

                                      -7-
<PAGE>

               (g)  any   declaration  or  payment  of  any  dividend  or  other
distribution  of assets of the Company or the adoption or  consideration  of any
plan or arrangement with respect thereto;

               (h) any  resignation  or  termination  of  employment  of any key
employee of the Company (other than terminations of temporary  employment during
university  leaves of absence),  or to the  Company's  knowledge  any plans with
respect thereto;

               (i) to the Company's  knowledge,  any other event or condition of
any  character  which  might   materially  and  adversely   affect  the  assets,
properties,  financial  condition,  operating results or business of the Company
(as such business is currently conducted and as it is proposed to be conducted);
or

               (j) any material  change in the Company's  accounting or internal
control procedures and practices.

          3.23  REAL PROPERTY  HOLDING  COMPANY.  The Company is not and has not
been at any time a "United States real property holding  corporation" as defined
in Section 897 of the Internal Revenue Code of 1986, as amended.

          3.24 INVESTMENT COMPANY.  The Company is not, and after the receipt of
the proceeds from the sale of the Shares  hereunder  will not be, an "investment
company"  within the meaning of the Investment  Company Act of 1940, as amended.

          3.25  MINUTES.  The  minute  books of the  Company  contain a complete
summary  of all  meetings  of  directors  and  shareholders  since  the  time of
incorporation.

          3.26 HOLDING COMPANY STATUS.  The Company is not a "holding  company,"
or a subsidiary or affiliate of a "holding  company," or a "subsidiary  company"
of a "holding  company," or a "public utility," within the meaning of the Public
Utility  Holding Company Act of 1935, as amended,  or a "public  utility" within
the meaning of the Federal Power Act, as amended.

          3.27 ACCOUNTING. The Company maintains and will continue to maintain a
system of accounting  established and  administered in accordance with generally
accepted  accounting  principles and has in place reasonable  internal  controls
which  are  adequate  and  appropriate  for  the  Company.

          3.28 SECTION 1202  COMPLIANCE.  The Company is a "C"  corporation  for
federal income tax purposes, is an "eligible  corporation" as defined in Section
1202(e)(4) of the Internal  Revenue Code of 1986, as amended (the "Code") and is
engaged in a "qualified  trade or business" as defined in Section  1202(e)(3) of
the Code.

               (a)  During the one-year  period  beginning  on the date one year
before the Closing,  the Company has not made one or more purchases of its stock
with an aggregate value (as of the time of the respective  purchases)  exceeding

                                      -8-
<PAGE>

5% of the  aggregate  value  of all of its  stock  as of the  beginning  of such
period.

               (b) At all times during the period that began with the  formation
of the  Company  and ends on the  Closing,  the  aggregate  gross  assets of the
Company did not exceed $50,000,000. For purposes of this representation, (i) the
amount received by the Company from the sale of its stock as contemplated herein
shall be taken into account, (ii) "aggregate gross assets" shall mean the amount
of (A) cash, (B) the aggregate fair market value of all property  contributed to
the  Company (or other  property  with a basis  determined  in whole or part for
federal  income tax purposes by  reference to the adjusted  basis of property so
contributed) as of the date of such contribution, and (C) the aggregate adjusted
basis for federal income tax purposes of other property held by the Company, and
(iii) the Company  shall be deemed to own its ratable share of the assets of its
subsidiaries, if any.

               (c) Ten  percent  or less of the  total  value  of the  Company's
assets  as of the  Closing  consists  of real  property  that is not used in the
Company's business.

               (d) Ten  percent  or less of the  total  value  of the  Company's
assets  (in  excess  of  liabilities)  as of the  Closing  consists  of stock or
securities in other corporations that are not subsidiaries of the Company (other
than assets described in Section 1202(e)(6) of the Code).

          3.29  SECTION  83(B) ELECTIONS.  All  elections  notices  permitted by
Section  83(b) of the Internal  Revenue  Code and any  analogous  provisions  of
applicable  state tax laws  have been  timely  filed by all  employees  who have
purchased shares of the Company's Common Stock under agreements that provide for
the  vesting of such  shares.

          3.30  MATERIAL LIABILITIES.  The Company has no material  liability or
obligation,  absolute or contingent  (individually or in the aggregate),  except
(i) obligation and liabilities  incurred after the date of  incorporation in the
ordinary  course  of  business  that are not  material,  individually  or in the
aggregate,  and (ii) obligations  under contracts made in the ordinary course of
business  that would not be required to be  reflected  in  financial  statements
prepared in accordance with generally accepted accounting principles.

          3.31  RELATED-PARTY TRANSACTIONS.

               (a) No employee, officer,  shareholder,  director or affiliate of
the Company,  or any member of his or her immediate  family, or any affiliate of
any of the  foregoing,  is indebted to the Company.  The Company is not indebted
(or  committed  to make  loans  or  extend  or  guaranty  credit)  to any of the
foregoing,  other than for (i) the payment of salary for services rendered, (ii)
reimbursement for reasonable expenses incurred on behalf of the Company,  and/or
(iii)  other  standard  employee  benefits  made  generally   available  to  all
employees.

               (b)  To  the  Company's  knowledge,  none  of  such  persons  is,
directly,  or indirectly,  interested in any material  contract with the Company
(other than such  contracts  as relate to any such persons  employment  with the
Company or ownership of capital stock of the Company).

                                      -9-
<PAGE>

               (c) To the  Company's  knowledge,  none of such  persons  has any
direct or indirect  ownership interest in any firm or corporation with which the
Company is affiliated or with which the Company has a business relationship.

               (d) To the  Company's  knowledge,  none of such  persons  has any
direct or indirect  ownership  interest in any firm or corporation that competes
with the  Company,  except that such  persons  may own stock in publicly  traded
companies  (not  exceeding  one percent of such  company's  outstanding  capital
stock) that may compete with the Company.

          3.32  STOCK  CERTIFICATES.  The  certificates  for  the  Shares  to be
delivered to the Investors  are in due and proper form,  have been duly executed
and will be  delivered by the Company  within three (3) days of the Closing.

     4.   REPRESENTATIONS AND WARRANTIES OF THE INVESTORS.  Each Investor, as to
such Investor only, hereby represents and warrants to the Company as follows:

          4.1 AUTHORIZATION.  This Agreement and the Ancillary Agreements,  when
executed  and  delivered by such  Investor,  will  constitute  valid and legally
binding obligations of the Investor, enforceable in accordance with the terms of
each agreement, except (i) as limited by laws of general application relating to
bankruptcy,  insolvency  and the relief of debtors,  (ii) as limited by rules of
law  governing  specific  performance,  injunctive  relief  or  other  equitable
remedies  and by  general  principles  of  equity,  and (iii) to the  extent the
indemnification  provisions  contained in the  Investor  Rights'  Agreement  may
further be limited by applicable laws and principles of public policy.

          4.2  EXPERIENCED  ACCREDITED  INVESTOR.  Such Investor has substantial
experience in  evaluating  and investing in private  placement  transactions  of
securities  in  companies  similar  to the  Company  so  that it is  capable  of
evaluating  the merits and risks of its  investment  in the  Company and has the
capacity to protect its own interests. Such Investor is an "accredited investor"
within the meaning of Rule 501 of  Regulation  D under the Act, as  presently in
effect.

          4.3  INVESTMENT.  Such  Investor  is  acquiring  the  Shares  and  the
Conversion Stock for investment for its own account,  not as a nominee or agent,
and not with the view to, or for resale in  connection  with,  any  distribution
thereof.  The Investor understands that the Shares and the Conversion Stock have
not been,  and will not be,  registered  under  the Act by reason of a  specific
exemption from the registration provisions of the Act, the availability of which
depends upon, among other things,  the bona fide nature of the investment intent
and the accuracy of such Investor's  representations  as expressed  herein.

          4.4  RESTRICTED SECURITIES.  The Investor  understands that the Shares
and the Conversion Stock are characterized as "restricted  securities" under the
federal  securities laws inasmuch as they are being acquired from the Company in
a  transaction  not  involving  a public  offering  and that under such laws and
applicable  regulations such securities may be resold without registration under
the Act, only in certain limited circumstances. In this connection, the Investor
represents  that it is familiar with Rule 144  promulgated  under the Act by the

                                      -10-
<PAGE>

Securities  and Exchange  Commission,  as presently in effect ("RULE 144"),  and
understands the resale  limitations  imposed thereby and by the Act.

          4.5  FURTHER LIMITATIONS ON  DISPOSITION.  Without in any way limiting
the representations set forth above, the Investor further agrees not to make any
disposition of all or any portion of the Shares or the  Conversion  Stock unless
and until the transferee has agreed in writing for the benefit of the Company to
be bound by this  Section 4 and the  Ancillary  Agreements,  provided and to the
extent this Section and such agreements are then  applicable,  and:

               (a) There is then in effect a  registration  statement  under the
Act  covering  such  proposed  disposition  and  such  disposition  is  made  in
accordance with such registration statement; or

               (b) (i) The  Investor  shall  have  notified  the  Company of the
proposed  disposition  and shall  have  furnished  the  Company  with a detailed
statement of the circumstances  surrounding the proposed disposition and (ii) if
reasonably  requested by the  Company,  the Investor  shall have  furnished  the
Company with an opinion of counsel,  reasonably satisfactory to the Company that
such disposition will not require  registration of such shares under the Act. It
is agreed that the Company will not require opinions of counsel for transactions
made pursuant to Rule 144 except in unusual circumstances.

               (c)  Notwithstanding  the  provisions of  paragraphs  (a) and (b)
above, no such  registration  statement or opinion of counsel shall be necessary
for a  transfer  by the  Investor  that is a  partnership  to a partner  of such
partnership or a retired partner of such  partnership who retires after the date
hereof,  or to the estate of any such partner or retired partner or the transfer
by gift, will or intestate  succession of any partner to his or her spouse or to
the  siblings,  lineal  descendants  or  ancestors of such partner or his or her
spouse,  if the transferee  agrees in writing to be subject to the terms of this
Agreement and the  Ancillary  Agreements to the same extent as if he or she were
an original Investor hereunder.

          4.6  NO PUBLIC MARKET.  The Investor understands that no public market
now exists for any of the securities  issued by the Company and that the Company
has made no  assurances  that a public  market will ever exist for the Company's
securities.

          4.7 ACCESS TO DATA. The Investor has had an opportunity to discuss the
Company's  business,   management  and  financial  affairs  with  the  Company's
management  and has also had an  opportunity  to ask  questions of the Company's
officers,  which  questions  were answered to its  satisfaction.

          4.8  BROKERS OR FINDERS.  The  Investor  has not engaged any  brokers,
finders,  or  agents  and has not  incurred,  and will not  incur,  directly  or
indirectly,  any liability for brokerage or finder's fee or agents'  commissions
or any similar  charges in connection  with this Agreement and the  transactions
contemplated  hereby.

                                      -11-
<PAGE>

     5.   CONDITIONS OF INVESTORS' OBLIGATIONS AT THE CLOSING.  Each  Investor's
obligation  to  purchase  Series C  Preferred  Stock at the  Closing  under this
Agreement is subject to the  fulfillment  on or prior to the Closing Date of the
following  conditions,  any of which  may be  waived in whole or in part by such
Investor:

          5.1  REPRESENTATIONS  AND  WARRANTIES  TRUE. The  representations  and
warranties  made by the Company in Section 3 hereof shall be true and correct on
the Closing  Date with the same force and effect as if they had been made on and
as of said  date.

          5.2 COVENANTS.  All covenants,  agreements and conditions contained in
this  Agreement  to be  performed by the Company on or prior to the Closing Date
shall have been performed or complied with.

          5.3 CONSENTS.  The Company  shall have obtained all consents,  permits
and waivers  necessary  to  consummate  the  transactions  contemplated  by this
Agreement.

          5.4  OPINION  OF THE  COMPANY'S  COUNSEL.  The  Investors  shall  have
received  from  Wilson  Sonsini  Goodrich  &  Rosati,  Professional  Corporation
("WSGR"),  counsel to the Company,  an opinion letter addressed to the Investors
in the form attached as EXHIBIT G dated as of the Closing Date.

          5.5  COMPLIANCE  CERTIFICATE.  The Company shall have delivered to the
Investors a certificate of the Company, executed by the Chief Executive Officer,
President or a Vice  President of the Company and dated as of the Closing  Date,
certifying to the  fulfillment of the conditions  specified in Sections 5.1, 5.2
and  5.3.

          5.6  CERTIFICATE  OF  INCORPORATION.   The  Restated   Certificate  in
substantially  the form  attached  as  EXHIBIT B shall  have been filed with the
Secretary  of State of the State of  Delaware.

          5.7 ANCILLARY  AGREEMENTS.  The Ancillary  Agreements  shall have been
executed by the Company and the Investors.

          5.8 PROCEEDINGS AND DOCUMENTS.  All corporate and other proceedings in
connection with the  transactions  contemplated at the Closing and all documents
and  instruments  incident  to such  transactions  shall  have  been  reasonably
approved  by the  Investors,  and the  Investors  shall have  received  all such
counterpart originals or certified or other copies of such documents as they may
reasonably  request.

          5.9  RESERVATION  OF CONVERSION  STOCK.  The shares of the  Conversion
Stock issuable upon  conversion of the Series C Preferred  Stock shall have been
duly authorized and reserved for issuance upon such conversion.

          5.10 COMPLIANCE WITH LAWS. The purchase of the Shares shall be legally
permitted by all laws and  regulations to which the Investors or the Company are
subject.

                                      -12-
<PAGE>

          5.11  BOARD OF DIRECTORS.  Immediately  after the Closing the Board of
Directors shall consist of Mark Auerbach,  Joseph Chang,  Michael Chang,  Joseph
Chow, Howard Lee, Alain Schreiber, and Chi Huey Wong.

          5.12  APPROVAL BY THE BOARD OF DIRECTORS OF PAR  PHARMACEUTICAL.  With
respect to any purchase of the Shares by Par Pharmaceutical, Inc., such purchase
shall be approved by the Board of Directors  of Par  Pharmaceutical,  Inc.

          5.13  MANAGEMENT  RIGHTS  LETTER.  To  the  extent  requested  by  Par
Pharmaceutical,  a Management  Rights Letter in a form reasonably  acceptable to
Par   Pharmaceutical   shall  have  been   executed   by  the  Company  and  Par
Pharmaceutical.

          5.14  SECURING OF ADDITIONAL  FUNDING.  The Company shall have secured
commitments  from  investors  to  purchase  an  aggregate  amount  of  at  least
$10,000,000 of the shares of the Company's Series D Preferred Stock (the "SERIES
D SHARES"),  including warrants to purchase shares of the Company's Common Stock
(the  "WARRANTS"),  to be  governed by a stock and  warrant  purchase  agreement
similar to this  Agreement and the  Ancillary  Agreements  ("ADDITIONAL  FUNDING
AGREEMENTS").  The  initial  closing  of the  purchase  and sale of the Series D
Shares and the  Warrants  shall be  consummated  concurrently  with the  Closing
contemplated hereby.

     6.   CONDITIONS  TO COMPANY'S  OBLIGATIONS  AT THE CLOSING.  The  Company's
obligation  to sell and issue the  Series C  Preferred  Stock at the  Closing is
subject to the  fulfillment  on or prior to the  Closing  Date of the  following
conditions,  any of which  may be  waived  in  whole  or in part by the  Company
(unless  the  Company  shall  have  contributed  in  whole  or in  part  to  the
nonoccurrence or nonfulfillment of such condition):

          6.1  REPRESENTATIONS  AND  WARRANTIES  TRUE. The  representations  and
warranties made by the Investors herein shall be true and correct on the Closing
Date with the same  force  and  effect as if they had been made on and as of the
same date.

          6.2 CONSENTS.  The Company  shall have obtained all consents,  permits
and waivers  necessary  or  appropriate  for  consummation  of the  transactions
contemplated  by this Agreement  which need to be obtained prior to the Closing.

          6.3  CERTIFICATE  OF  INCORPORATION.  The Company shall have filed the
Restated  Certificate in  substantially  the form attached as EXHIBIT B with the
Secretary of State of the State of Delaware on or prior to the Closing Date.

          6.4 ANCILLARY  AGREEMENTS.  The Ancillary  Agreements  shall have been
executed by the Company and the Investors.

          6.5  COMPLIANCE  WITH ALL  LAWS.  At the  Closing,  the  purchase  and
issuance  of the Shares  hereunder  shall be legally  permitted  by all laws and
regulations to which the Investors or the Company are subject.

                                      -13-
<PAGE>

     7.   MISCELLANEOUS.

          7.1 GOVERNING LAW. This  Agreement  shall be governed by and construed
under the laws of the State of Delaware as applied to agreements  among Delaware
residents, made and to be performed entirely within the State of Delaware.

          7.2  SURVIVAL.  The  representations,   warranties,   covenants,   and
agreements made herein shall survive any investigation made by the Investors and
the  closing of the  transactions  contemplated  hereby.  All  statements  as to
factual matters contained in any certificate or other instrument delivered by or
on behalf of the Company  pursuant hereto or in connection with the transactions
contemplated  hereby shall be deemed to be representations and warranties by the
Company hereunder as of the date of such certificate or instrument.

          7.3 FINDER'S FEE. Except as set forth on Schedule 7.3 attached hereto,
each  party  represents,  as to  itself  only,  that it  neither  is nor will be
obligated  for  any  finder's  fee  or   commission  in  connection   with  this
transaction.  The Investors (severally but not jointly) and the Company agree to
indemnify  and  hold  harmless  the  other  party  from  any  liability  for any
commission  or  compensation  in the nature of a finder's fee (and the costs and
expenses of defending  against such  liability or asserted  liability) for which
the Investors or the Company is responsible.

          7.4  SUCCESSORS AND ASSIGNS.  Except as otherwise  expressly  provided
herein,  the  provisions  hereof  shall  inure to the benefit of, and be binding
upon, the successors,  assigns,  heirs,  executors,  and  administrators  of the
parties  hereto.

          7.5  ENTIRE AGREEMENT.  This  Agreement,  the Exhibits,  the Ancillary
Agreements  and the other  documents  delivered  pursuant to this  Agreement  or
contemplated  hereby constitute the full and entire  understanding and agreement
among the parties  with regard to the  subjects  hereof and thereof and no party
shall  be  liable  or  bound  to  any   other   party  in  any   manner  by  any
representations, warranties, covenants, or agreements except as specifically set
forth  herein  or  therein.  Nothing  in this  Agreement,  the  Exhibits  or the
Ancillary Agreements,  express or implied, is intended to confer upon any party,
other than the parties  hereto and thereto and their  respective  successors and
assigns, any rights, remedies, obligations, or liabilities under or by reason of
this Agreement,  the Exhibits or the Ancillary  Agreements,  except as expressly
provided  herein and therein.

          7.6  SEVERABILITY.  In case any provision of this Agreement becomes or
is declared by a court of competent jurisdiction to be illegal, unenforceable or
void,  this  Agreement  shall  continue  in full force and effect  without  said
provision; PROVIDED, HOWEVER, that no such severability shall be effective if it
materially  changes the economic  benefit of this  Agreement  to any party.

          7.7  AMENDMENT AND WAIVER.  Any term of this  Agreement may be amended
and the observance of any term of this Agreement may be waived (either generally
or in a particular  instance and either  retroactively or  prospectively),  only
with the  written  consent of the  Company  and the holders of a majority of the
shares of the Common Stock  issued or issuable  upon  conversion  of the Shares;
PROVIDED  that no amendment of this  Agreement  shall (i) increase any financial

                                      -14-
<PAGE>

obligation or liability of an Investor or holder beyond that set forth herein or
permitted  hereby without such  Investor's or holder's  written  consent or (ii)
materially and adversely  affect the rights of an Investor or holder in a manner
that    discriminates    against   such    Investor/holder    vis-a-vis    other
Investors/holders  without such Investor/holder's written consent. Any amendment
or waiver  effected in  accordance  with this  Section 7.7 shall be binding upon
each  holder  of any then  outstanding  shares  of the  Common  Stock  issued or
issuable  upon  conversion  of the  Shares,  each  future  holder  of  all  such
securities  and the Company.

          7.8  DELAYS OR OMISSIONS.  No delay or omission to exercise any right,
power,  or remedy  accruing to the  Investors  or any  subsequent  holder of any
Shares or  Conversion  Stock upon any breach,  default or  noncompliance  of the
Company under this Agreement or under the Restated Certificate, shall impair any
such right,  power,  or remedy,  nor shall it be construed to be a waiver of any
such breach,  default or noncompliance,  or any acquiescence  therein, or of any
similar breach,  default or noncompliance  thereafter  occurring.  It is further
agreed that any waiver, permit, consent, or approval of any kind or character on
the Investors' part of any breach, default or noncompliance under this Agreement
or under the Restated  Certificate or any waiver on the  Investors'  part of any
provisions  or  conditions  of this  Agreement  must be in writing  and shall be
effective only to the extent  specifically  set forth in such writing,  and that
all remedies,  either under this Agreement, the Restated Certificate,  Bylaw, or
otherwise  afforded to the Investors,  shall be cumulative and not  alternative.

          7.9 NOTICES.  Any notice required or permitted by this Agreement shall
be in writing and shall be deemed  effectively  given: (a) upon actual delivery,
when delivered  personally;  (b) upon receipt when sent by confirmed telegram or
fax if sent during normal business hours,  and if not, then on the next business
day; (c) one day after deposit with a nationally  recognized  overnight courier,
specifying next day delivery,  with written verification of receipt; or (d) four
business days after being deposited in the U.S. mail, as certified or registered
mail, return receipt requested,  postage prepaid.  All  communications  shall be
sent to the Company and to the  Investors  at the  addresses as set forth on the
signature  page hereof or at such other  address as the Company or Investors may
designate by ten (10) days advance written notice to the other parties hereto.

          7.10 EXPENSES. The Company and the Investors shall each bear their own
expenses and legal fees in connection with the consummation of this transaction.

          7.11  TITLES  AND  SUBTITLES.  The  titles  of the  sections  of  this
Agreement are for  convenience of reference only and are not to be considered in
construing this Agreement.

          7.12  COUNTERPARTS.  This  Agreement  may be executed in any number of
counterparts,  each of  which  shall be  deemed  an  original,  but all of which
together shall  constitute one  instrument.

          7.13 INDEMNIFICATION.  The Company assumes liability for and agrees to
indemnify,  defend and hold harmless each Investor (the  "INDEMNIFIED  PERSONS")
from and against, all losses, claims, damages, liabilities,  obligations, fines,
penalties, judgments,  settlements, costs, expenses and disbursements (including
attorneys'  fees and  expenses)  (collectively,  "LOSSES") (i) arising out of or

                                      -15-
<PAGE>

related to any breach or  inaccuracy  of any  representation  or warranty of the
Company contained in this Agreement;  (ii) any  non-fulfillment or breach of any
covenant or  agreement  of the Company  contained  in this  Agreement;  or (iii)
incurred in connection with any action or proceeding  against the Company or any
Indemnified  Person (a  "PROCEEDING")  arising out of or in connection with this
Agreement  or any other  document  or  instrument  executed  pursuant  hereto or
thereto,  or the transactions  contemplated herein or therein to the full extent
permitted by applicable  law,  other than Losses that are finally  determined in
such  Proceeding  to be  primarily  and  directly  a  result  of (1)  the  gross
negligence of such Indemnified Person, (2) a breach of a fiduciary duty, if any,
owed by such Indemnified Person to the Company,  (3) the willful misconduct or a
knowing  violation  of  applicable  law by  such  Indemnified  Person,  or (4) a
transaction  from which such  Indemnified  Person received an improper  personal
benefit.  The obligations of the Company to each  Indemnified  Person under this
Section 7.13 will be separate and distinct obligations.

                  [Remainder of page intentionally left blank.]














                                      -16-
<PAGE>


          The foregoing Series C Preferred Stock Purchase  Agreement is executed
as of the date first above written.

                                   COMPANY:

                                   OPTIMER PHARMACEUTICALS, INC.

                                   By: _________________________________________
                                       Michael N. Chang, Chief Executive Officer



















                          OPTIMER PHARMACEUTICALS, INC.
          SIGNATURE PAGE TO SERIES C PREFERRED STOCK PURCHASE AGREEMENT
<PAGE>


          The foregoing Series C Preferred Stock Purchase  Agreement is executed
as of the date first above written.



                                       INVESTOR:

                                       PAR PHARMACEUTICAL, INC.

                                       By: _____________________________________

                                       Name:____________________________________

                                       Title: __________________________________



















                          OPTIMER PHARMACEUTICALS, INC.
          SIGNATURE PAGE TO SERIES C PREFERRED STOCK PURCHASE AGREEMENT

<PAGE>


                                    EXHIBIT A


                              SCHEDULE OF INVESTORS

                                    INVESTORS

<TABLE>
<CAPTION>
                                                        NUMBER OF
              INVESTOR                              SERIES C SHARES        PURCHASE PRICE
              --------                              ---------------        ---------------
<S>                                                   <C>                  <C>
PAR PHARMACEUTICAL, INC.                              3,333,333            $ 11,999,998.00
300 Tice Boulevard
Woodcliff, New Jersey 07677
Fax #  (201)391-5364
Attention: Paul V. Campanelli, Senior Vice
President, Business Development
Attention: Thomas J. Haughey, Vice President
& General Counsel

                          TOTAL                       3,333,333            $ 11,999,998.00

</TABLE>