<PAGE>

                                                                     Exhibit 4.4

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS
AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE,
PLEDGED, OR HYPOTHECATED EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT OF 1933
ACT AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAWS.

                                WARRANT AGREEMENT

              To Purchase Shares of the Series D Preferred Stock of

                         Quatrx Pharmaceuticals Company

               Dated as of January 26, 2006 (the "EFFECTIVE DATE")

         WHEREAS, Quatrx Pharmaceuticals Company, a Delaware corporation (the
"COMPANY"), has entered into a Senior Loan and Security Agreement of even date
herewith (the "LOAN AGREEMENT") with Hercules Technology Growth Capital, Inc., a
Maryland corporation (the "WARRANTHOLDER");

         WHEREAS, the Company desires to grant to Warrantholder, in
consideration for, among other things, the financial accommodations provided for
in the Loan Agreement, the right to purchase shares of its Series D Preferred
Stock pursuant to this Warrant Agreement (the "Agreement");

      NOW, THEREFORE, the Company and Warrantholder agree as follows:

1.    GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

      For value received, the Company hereby grants to the Warrantholder, and
the Warrantholder is entitled, upon the terms and subject to the conditions
hereinafter set forth, to subscribe for and purchase, from the Company, 964,286
fully paid and non-assessable shares of the Preferred Stock (as defined below).
The per share exercise price (the "EXERCISE PRICE") shall be equal to $1.40. If
the Company completes an Initial Public Offering before October 30, 2006, the
Exercise Price will be adjusted to be the time-weighted average price between
the Series D price per share and the Initial Public Offering price per share (up
to a maximum pre-money valuation of $250,000,000 for calculation purposes only).
The price will be time-weighted between the date of the last tranche of the
Series D (October 13, 2005), the date the term sheet was signed (December 26,
2005) and the date of the Initial Public Offering. For illustration of that
formula, (a) if the term sheet date is December 26, 2005, the last tranche of
the last equity round is $1.40 per share on October 13, 2005, and the Initial
Public Offering is October 12, 2006 at $10.00 per share, (b) the formula is
((Number of days from last equity round to term sheet date)/(Number of days from
last equity round to public offering) x (price of next equity round - last
equity round)) + last equity round, and (c) the calculation is ((74 days/364
days) x ($10.00-$1.40)) + $1.40 = $3.15.

In that case, the number of shares to be purchased will be equal to $1,350,000
divided by such adjusted Exercise Price.

                                       1.
<PAGE>



      If the Company does not complete an Initial Public Offering before October
30, 2006, and sells or issues equity securities (the "Next Round Stock")
thereafter for less than $1.40 per share, the "Preferred Stock" shall mean the
Next Round Stock, and not Series D Preferred Stock, and the price will be
time-weighted between October 13, 2005, December 26, 2005, and the date that the
Next Round Stock is sold or issued. In that case, the number of shares to be
purchased will be equal to $1,350,000 divided by such adjusted Exercise Price.
The number and Exercise Price of such shares are subject to adjustment as
provided in Section 8. As used herein, the following terms shall have the
following meanings:

                  "ACT" means the Securities Exchange Act of 1933, as amended.

                  "CHARTER" means the Company's Certificate of Incorporation, as
may be amended from time to time.

                  "COMMON STOCK" means the Company's common stock;

                  "INITIAL PUBLIC OFFERING" means the initial underwritten
public offering of the Company's Common Stock pursuant to a registration
statement under the Act, which public offering has been declared effective by
the Securities and Exchange Commission ("SEC");

                  "MERGER EVENT" means (i) a merger or consolidation involving
the Company in which the Company is not the surviving entity, or in which the
outstanding shares of the Company's capital stock are otherwise converted into
or exchanged for shares of capital stock of another entity or (ii) a sale,
lease, license or transfer of all or substantially all of the assets of the
Company outside the ordinary course of business.

                  "PREFERRED STOCK" means the Series D Preferred Stock of the
Company and any other stock into or for which the Series D Preferred Stock may
be converted or exchanged, and upon and after the occurrence of an event which
results in the automatic or voluntary conversion, redemption or retirement of
all (but not less than all) of the outstanding shares of such Preferred Stock,
including, without limitation, the consummation of an Initial Public Offering of
the Common Stock in which such a conversion occurs, then from and after the date
upon which such outstanding shares are so converted, redeemed or retired,
"Preferred Stock" shall mean such Common Stock; and

                  "PURCHASE PRICE" means, with respect to any exercise of this
Warrant, an amount equal to the Exercise Price as of the relevant time
multiplied by the number of shares of Preferred Stock requested to be exercised
under this Warrant pursuant to such exercise.

2.    TERM OF THE AGREEMENT.

      Except as otherwise provided for herein, the term of this Warrant and the
right to purchase Preferred Stock as granted herein (the "Warrant) shall
commence on the Effective Date and shall be exercisable for a period ending upon
the earliest to occur of (i) January 26, 2013 or (ii) three (3) years after the
date of the Initial Public Offering, or (iii) a Merger Event in which the
consideration consists entirely of (a) cash and/or (b) freely tradable public
securities.

                                       2.
<PAGE>

3.    EXERCISE OF THE PURCHASE RIGHTS.

      (A) EXERCISE. The purchase rights set forth in this Warrant are
exercisable by the Warrantholder, in whole or in part, at any time, or from time
to time, prior to the expiration of the term set forth in Section 2, by
tendering to the Company at its principal office a notice of exercise in the
form attached hereto as EXHIBIT I (the "NOTICE OF EXERCISE"), duly completed and
executed. Promptly upon receipt of the Notice of Exercise and the payment of the
Purchase Price in accordance with the terms set forth below, and in no event
later than three (3) business days thereafter, the Company shall issue to the
Warrantholder a certificate for the number of shares of Preferred Stock
purchased and shall execute the acknowledgment of exercise in the form attached
hereto as EXHIBIT II (the "ACKNOWLEDGMENT OF EXERCISE") indicating the number of
shares which remain subject to future purchases, if any.

      The Purchase Price may be paid at the Warrantholder's election either (i)
by cash or check, or (ii) by surrender of all or a portion of the Warrant for
shares of Preferred Stock to be exercised under this Warrant and, if applicable,
an amended Agreement representing the remaining number of shares purchasable
hereunder, as determined below ("NET ISSUANCE"). If the Warrantholder elects the
Net Issuance method, the Company will issue Preferred Stock in accordance with
the following formula:

                        X = Y(A-B)
                            -----
                              A

Where:            X =   the number of shares of Preferred Stock to be issued
                        to the Warrantholder.

                  Y =   the number of shares of Preferred Stock requested to
                        be exercised under this Warrant.

                  A =   the fair market value of one (1) share of Preferred
                        Stock at the time of issuance of such shares of
                        Preferred Stock.

                  B =   the Exercise Price.

                  For purposes of the above calculation, current fair market
value of Preferred Stock shall mean with respect to each share of Preferred
Stock:

                  (I) if the exercise is in connection with an Initial Public
Offering, and if the Company's Registration Statement relating to such Initial
Public Offering has been declared effective by the SEC, then the fair market
value per share shall be the product of (x) the initial "Price to Public" of the
Common Stock specified in the final prospectus with respect to the offering and
(y) the number of shares of Common Stock into which each share of Preferred
Stock is convertible at the time of such exercise;

                  (II) if the exercise is after, and not in connection with, an
Initial Public Offering, and:

                        (1) if the Common Stock is traded on a securities
exchange (which shall include the NASDAQ National Market), the fair market value
shall be deemed to be the


                                       3.
<PAGE>

product of (x) the average of the closing prices over a ten (10) day period
ending three days before the day the current fair market value of the securities
is being determined and (y) the number of shares of Common Stock into which each
share of Preferred Stock is convertible at the time of such exercise; or

                        (2) if the Common Stock is actively traded
over-the-counter, the fair market value shall be deemed to be the product of (x)
the average of the closing bid and asked prices quoted on the NASDAQ system (or
similar system) over the ten (10) day period ending three days before the day
the current fair market value of the securities is being determined and (y) the
number of shares of Common Stock into which each share of Preferred Stock is
convertible at the time of such exercise;

                  (III) if at any time the Common Stock is not listed on any
securities exchange or quoted in the NASDAQ National Market or the
over-the-counter market, the current fair market value of Preferred Stock shall
be the product of (x) the highest price per share which the Company could obtain
from a willing buyer (not a current employee or director) for shares of Common
Stock sold by the Company, from authorized but unissued shares, as most recently
determined in good faith by its Board of Directors and (y) the number of shares
of Common Stock into which each share of Preferred Stock is convertible at the
time of such exercise, unless the Company shall become subject to a Merger Event
pursuant to which the Company is not the surviving party, in which case the fair
market value of Preferred Stock shall be deemed to be the per share value
received by the holders of the Company's Preferred Stock on a common equivalent
basis pursuant to such Merger Event.

      Upon partial exercise by either cash or Net Issuance, the Company shall
promptly issue an amended Agreement representing the remaining number of shares
purchasable hereunder. All other terms and conditions of such amended Agreement
shall be identical to those contained herein, including, but not limited to the
Effective Date hereof.

      (B) EXERCISE PRIOR TO EXPIRATION. To the extent this Warrant is not
previously exercised as to all Preferred Stock subject hereto, and if the fair
market value of one share of the Preferred Stock is greater than the Exercise
Price then in effect, this Warrant shall be deemed automatically exercised
pursuant to Section 3(a) (even if not surrendered) immediately before its
expiration. For purposes of such automatic exercise, the fair market value of
one share of the Preferred Stock upon such expiration shall be determined
pursuant to Section 3(a). To the extent this Warrant or any portion thereof is
deemed automatically exercised pursuant to this Section 3(b), the Company agrees
to promptly notify the Warrantholder of the number of shares of Preferred Stock,
if any, the Warrantholder is to receive by reason of such automatic exercise.

4.    RESERVATION OF SHARES.

      During the term of this Warrant, the Company will at all times have
authorized and reserved a sufficient number of shares of its Preferred Stock to
provide for the exercise of the rights to purchase Preferred Stock as provided
for herein, and shall have authorized and reserved a sufficient number of shares
of its Common Stock to provide for the conversion of the Preferred Shares
available hereunder.


                                       4.
<PAGE>


5.    NO FRACTIONAL SHARES OR SCRIP.

      No fractional shares or scrip representing fractional shares shall be
issued upon the exercise of this Warrant, but in lieu of such fractional shares
the Company shall make a cash payment therefor upon the basis of the Exercise
Price then in effect.

6.    NO RIGHTS AS SHAREHOLDER.

      This Warrant does not entitle the Warrantholder to any voting rights or
other rights as a shareholder of the Company prior to the exercise of this
Warrant.

7.    WARRANTHOLDER REGISTRY.

      The Company shall maintain a registry showing the name and address of the
registered holder of this Warrant. Warrantholder's initial address, for purposes
of such registry, is set forth below Warrantholder's signature on this Warrant.
Warrantholder may change such address by giving written notice of such changed
address to the Company.

8.    ADJUSTMENT RIGHTS.

      The Exercise Price and the number of shares of Preferred Stock purchasable
hereunder are subject to adjustment, as follows:

      (A) MERGER EVENT. If at any time there shall be Merger Event in which the
term of the Warrant does not expire, then, as a part of such Merger Event,
lawful provision shall be made so that the Warrantholder shall thereafter be
entitled to receive, upon exercise of this Warrant, the number of shares of
preferred stock or other securities or property of the successor corporation
resulting from such Merger Event that would have been issuable if Warrantholder
had exercised this Warrant immediately prior to the Merger Event.

      (B) RECLASSIFICATION OF SHARES. Except as set forth in Section 8(a), if
the Company at any time shall, by combination, reclassification, exchange or
subdivision of securities or otherwise, change any of the securities as to which
purchase rights under this Warrant exist into the same or a different number of
securities of any other class or classes, this Warrant shall thereafter
represent the right to acquire such number and kind of securities as would have
been issuable as the result of such change with respect to the securities which
were subject to the purchase rights under this Warrant immediately prior to such
combination, reclassification, exchange, subdivision or other change.

      (C) SUBDIVISION OR COMBINATION OF SHARES. If the Company at any time shall
combine or subdivide its Preferred Stock, (i) in the case of a subdivision, the
Exercise Price shall be proportionately decreased, and the number of shares of
Preferred Stock issuable upon exercise of this Warrant shall be proportionately
increased, or (ii) in the case of a combination, the Exercise Price shall be
proportionately increased, and the number of shares of Preferred Stock issuable
upon the exercise of this Warrant shall be proportionately decreased. If the
Company at any time shall combine or subdivide its Common Stock, the conversion
of Preferred Stock to Common Stock shall be adjusted in accordance with the
Company's Certificate of Incorporation.

                                       5.
<PAGE>

      (D) STOCK DIVIDENDS. If the Company at any time while this Warrant is
outstanding and unexpired shall:

            (I) pay a dividend with respect to the Preferred Stock payable in
Preferred Stock, then the Exercise Price shall be adjusted, from and after the
date of determination of shareholders entitled to receive such dividend or
distribution, to that price determined by multiplying the Exercise Price in
effect immediately prior to such date of determination by a fraction (A) the
numerator of which shall be the total number of shares of Preferred Stock
outstanding immediately prior to such dividend or distribution, and (B) the
denominator of which shall be the total number of shares of Preferred Stock
outstanding immediately after such dividend or distribution; or

            (II) make any other distribution with respect to Preferred Stock (or
stock into which the Preferred Stock is convertible), except any distribution
specifically provided for in any other clause of this Section 8, then, in each
such case, provision shall be made by the Company such that the Warrantholder
shall receive upon exercise or conversion of this Warrant a proportionate share
of any such distribution as though it were the holder of the Preferred Stock (or
other stock for which the Preferred Stock is convertible) as of the record date
fixed for the determination of the shareholders of the Company entitled to
receive such distribution.

      (E) ANTIDILUTION RIGHTS. Additional antidilution rights applicable to the
Preferred Stock purchasable hereunder are as set forth in the Company's Charter
and shall be applicable with respect to the Preferred Stock issuable hereunder.
The Company shall promptly provide the Warrantholder with any restatement,
amendment, modification or waiver of the Charter that materially affects the
rights of the Preferred Stock; PROVIDED, that no such amendment, modification or
waiver shall impair or reduce the antidilution rights applicable to the
Preferred Stock as of the date hereof unless such amendment, modification or
waiver affects the rights of Warrantholder with respect to the Preferred Stock
in the same manner as it affects all other holders of Preferred Stock. For the
avoidance of doubt, there shall be no duplicate anti-dilution adjustment
pursuant to this subsection (e), the forgoing subsection (d) and the Company's
Charter.

      (F) NOTICE OF ADJUSTMENTS. Whenever an adjustment to the Exercise Price or
the number of shares of Preferred Stock issuable upon exercise of this Warrant
is made pursuant to this Section 8, the Company shall send to the Warrantholder
a notice setting forth, in reasonable detail, (i) the event requiring the
adjustment, (ii) the amount of such adjustment, (iii) the method by which such
adjustment was calculated, (iv) the adjusted Exercise Price (if the Exercise
Price has been adjusted), and (v) the number of shares subject to purchase
hereunder after giving effect to such adjustment, and shall cause such notice to
be mailed (by first class mail, postage prepaid, or by reputable overnight
courier with all charges prepaid) within thirty (30) days of such adjustment
addressed to the Warrantholder at the address for Warrantholder set forth in the
registry referred to in Section 7.

9.    REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

      (A) RESERVATION OF PREFERRED STOCK. The Preferred Stock issuable upon
exercise of the Warrantholder's rights has been duly and validly reserved and,
when issued in accordance


                                       6.
<PAGE>

with the provisions of this Warrant, will be validly issued, fully paid and
non-assessable, and will be free of any taxes, liens, charges or encumbrances of
any nature whatsoever; PROVIDED, that the Preferred Stock issuable pursuant to
this Warrant may be subject to restrictions on transfer under state and/or
federal securities laws and applicable agreements to which the Company or its
security holders are parties. The Company has made available to the
Warrantholder true, correct and complete copies of its Charter and current
bylaws. The issuance of certificates for shares of Preferred Stock upon exercise
of this Warrant shall be made without charge to the Warrantholder for any
issuance tax in respect thereof, or other cost incurred by the Company in
connection with such exercise and the related issuance of shares of Preferred
Stock; PROVIDED, that the Company shall not be required to pay any tax which may
be payable in respect of any transfer and the issuance and delivery of any
certificate in a name other than that of the Warrantholder.

      (B) DUE AUTHORITY. The execution and delivery by the Company of this
Warrant and the performance of all obligations of the Company hereunder,
including the issuance to Warrantholder of the right to acquire the shares of
Preferred Stock and the Common Stock into which it may be converted, have been
duly authorized by all necessary corporate action on the part of the Company.
This Warrant: (1) is not inconsistent with the Company's Charter or current
bylaws; (2) does not contravene any law or governmental rule, regulation or
order applicable to it; and (3) does not and will not contravene any provision
of, or constitute a default under, any indenture, mortgage, contract or other
instrument to which it is a party or by which it is bound. This Warrant
constitutes a legal, valid and binding agreement of the Company, enforceable in
accordance with its respective terms.

      (C) CONSENTS AND APPROVALS. No consent or approval of, giving of notice
to, registration with, or taking of any other action in respect of any state,
federal or other governmental authority or agency is required with respect to
the execution, delivery and performance by the Company of its obligations under
this Warrant, except for the filing of notices pursuant to Regulation D under
the Act and any filing required by applicable state securities law, which
filings will be effective by the time required thereby.

      (D) ISSUED SECURITIES. All issued and outstanding shares of Common Stock,
Preferred Stock or any other securities of the Company have been duly authorized
and validly issued and are fully paid and nonassessable. Attached to this
Warrant is a true and correct capitalization table of the Company.

      (E) OTHER COMMITMENTS TO REGISTER SECURITIES. Except as set forth in this
Warrant and that certain Fourth Amended and Restated Investor Rights Agreement
by and between the Company and the parties named therein dated as of November
22, 2004, as amended by the Amendment to Fourth Amended and Restated Investors
Rights Agreement dated as of May 25, 2005 (the "Investor Rights Agreement"), the
Company is not, pursuant to the terms of any other agreement currently in
existence, under any obligation to register under the Act any of its presently
outstanding securities or any of its securities which may hereafter be issued.

      (F) EXEMPT TRANSACTION. Subject to the accuracy of the Warrantholder's
representations in Section 10, the issuance of the Preferred Stock upon exercise
of this Warrant, and the issuance of the Common Stock upon conversion of the
Preferred Stock, will each constitute a transaction exempt from (i) the
registration requirements of Section 5 of the Act, in


                                       7.







<PAGE>

reliance upon Section 4(2) thereof, and (ii) the qualification requirements of
the applicable state securities laws.

      (G) COMPLIANCE WITH RULE 144. If the Warrantholder proposes to sell
Preferred Stock issuable upon the exercise of this Warrant, or the Common Stock
into which it is convertible, in compliance with Rule 144 promulgated by the
SEC, then, upon Warrantholder's written request to the Company, the Company
shall furnish to the Warrantholder, within ten days after receipt of such
request, a written statement confirming the Company's compliance or
non-compliance, as the case may be, with the filing requirements of the SEC as
set forth in such Rule, as such Rule may be amended from time to time.

      (h) LOCKUP. The Warrantholder shall promptly execute any lock-up agreement
in connection with the Company's Initial Public Offering that is executed by all
of the Company's officers, directors and significant shareholders.

10.   REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

      This Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Warrantholder:

      (A) INVESTMENT PURPOSE. The right to acquire Preferred Stock or the
Preferred Stock issuable upon exercise of the Warrantholder's rights contained
herein will be acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Warrantholder has no present intention
of selling or engaging in any public distribution of the same except pursuant to
a registration or exemption.

      (B) PRIVATE ISSUE. The Warrantholder understands (i) that the Preferred
Stock issuable upon exercise of this Warrant is not registered under the Act or
qualified under applicable state securities laws on the ground that the issuance
contemplated by this Warrant will be exempt from the registration and
qualifications requirements thereof, and (ii) that the Company's reliance on
such exemption is predicated on the representations set forth in this Section
10.

      (C) DISPOSITION OF WARRANTHOLDER'S RIGHTS. In no event will the
Warrantholder make a disposition of any of its rights to acquire Preferred Stock
or Preferred Stock issuable upon exercise of such rights unless and until (i) it
shall have notified the Company of the proposed disposition, and (ii) if
requested by the Company, it shall have furnished the Company with an opinion of
counsel (which counsel may either be inside or outside counsel to the
Warrantholder) reasonably satisfactory to the Company and its counsel to the
effect that (A) appropriate action necessary for compliance with the Act has
been taken, or (B) an exemption from the registration requirements of the Act is
available. Notwithstanding the foregoing, the restrictions imposed upon the
transferability of any of its rights to acquire Preferred Stock or Preferred
Stock issuable on the exercise of such rights do not apply to transfers from the
beneficial owner of any of the aforementioned securities to its nominee or from
such nominee to its beneficial owner, or to any transfers to an Affiliate of
Warrantholder, and shall terminate as to any particular share of Preferred Stock
when (1) such security shall have been effectively registered under the Act and
sold by the holder thereof in accordance with such registration or


                                       8.
<PAGE>
(2) such security shall have been sold without registration in compliance with
Rule 144 under the Act, or (3) a letter shall have been issued to the
Warrantholder at its request by the staff of the SEC or a ruling shall have been
issued to the Warrantholder at its request by the SEC stating that no action
shall be recommended by such staff or taken by the SEC, as the case may be, if
such security is transferred without registration under the Act in accordance
with the conditions set forth in such letter or ruling and such letter or ruling
specifies that no subsequent restrictions on transfer are required. Whenever the
restrictions imposed hereunder shall terminate, as hereinabove provided, the
Warrantholder or holder of a share of Preferred Stock then outstanding as to
which such restrictions have terminated shall be entitled to receive from the
Company, without expense to such holder, one or more new certificates for this
Warrant or for such shares of Preferred Stock not bearing any restrictive
legend.

      (D) FINANCIAL RISK. The Warrantholder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment, and has the ability to bear the economic risks of its
investment.

      (E) RISK OF NO REGISTRATION. The Warrantholder understands that if the
Company does not register with the SEC pursuant to Section 12 of the Securities
Exchange Act of 1934, as amended (the "1934 ACT"), or file reports pursuant to
Section 15(d) of the 1934 Act, or if a registration statement covering the
securities under the Act is not in effect when it desires to sell (i) the rights
to purchase Preferred Stock pursuant to this Warrant or (ii) the Preferred Stock
issuable upon exercise of the right to purchase, it may be required to hold such
securities for an indefinite period. The Warrantholder also understands that any
sale of (A) its rights hereunder to purchase Preferred Stock or (B) Preferred
Stock issued or issuable hereunder which might be made by it in reliance upon
Rule 144 under the Act may be made only in accordance with the terms and
conditions of that Rule.

      (F) ACCREDITED INVESTOR. Warrantholder is an "accredited investor" within
the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

      (G) DILIGENCE. Warrantholder has had an opportunity to discuss the
Company's business, management and financial affairs with its management and an
opportunity to review the Company's facilities.

11.   TRANSFERS.

      Subject to the terms and conditions contained in Section 10, this Warrant
and all rights hereunder are transferable in whole or in part by the
Warrantholder and any successor transferee with the consent of the Company,
which consent shall not be unreasonably withheld [CONFORM TO EXISTING
SHAREHOLDER AGREEMENTS]. The transfer shall be recorded on the books of the
Company upon receipt by the Company of a notice of transfer in the form attached
hereto as Exhibit III (the "TRANSFER NOTICE"), at its principal offices and the
payment to the Company of all transfer taxes and other governmental charges
imposed on such transfer.


                                       9.
<PAGE>
12.   MISCELLANEOUS.

      (A) EFFECTIVE DATE. The provisions of this Warrant shall be construed and
shall be given effect in all respects as if it had been executed and delivered
by the Company on the date hereof. This Warrant shall be binding upon any
successors or assigns of the Company.

      (B) REMEDIES. In the event of any default hereunder, the non-defaulting
party may proceed to protect and enforce its rights either by suit in equity
and/or by action at law, including but not limited to an action for damages as a
result of any such default, and/or an action for specific performance for any
default where Warrantholder will not have an adequate remedy at law and where
damages will not be readily ascertainable.

      (C) NO IMPAIRMENT OF RIGHTS. The Company will not, by amendment of its
Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
actions as may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment.

      (D) SEVERABILITY. In the event any one or more of the provisions of this
Warrant shall for any reason be held invalid, illegal or unenforceable, the
remaining provisions of this Warrant shall be unimpaired, and the invalid,
illegal or unenforceable provision shall be replaced by a mutually acceptable
valid, legal and enforceable provision, which comes closest to the intention of
the parties underlying the invalid, illegal or unenforceable provision.

      (E) NOTICES. Except as otherwise provided herein, any notice, demand,
request, consent, approval, declaration, service of process or other
communication that is required, contemplated, or permitted under this Warrant or
with respect to the subject matter hereof shall be in writing, and shall be
deemed to have been validly served, given, delivered, and received upon the
earlier of: (i) the first business day after transmission by facsimile or hand
delivery or deposit with an overnight express service or overnight mail delivery
service; or (ii) the third calendar day after deposit in the United States
mails, with proper first class postage prepaid, and shall be addressed to the
party to be notified at the addresses set forth on the signature page hereto, or
to such other address as each party may designate for itself by like notice. A
notice delivered to the Company or Warrantholder shall be valid despite the
failure to deliver a copy of such notice to any other person.

      (F) ENTIRE AGREEMENT; AMENDMENTS. This Warrant constitute the entire
agreement and understanding of the parties hereto in respect of the subject
matter hereof, and supersede and replace in their entirety any prior proposals,
term sheets, letters, negotiations or other documents or agreements, whether
written or oral, with respect to the subject matter hereof. None of the terms of
this Warrant may be amended except by an instrument executed by each of the
parties hereto.

      (G) NO WAIVER. No omission or delay by Warrantholder at any time to
enforce any right or remedy reserved to it, or to require performance of any of
the terms, covenants or provisions hereof by the Company at any time designated,
shall be a waiver of any such right or


                                      10.
<PAGE>
remedy to which Warrantholder is entitled, nor shall it in any
way affect the right of Warrantholder to enforce such provisions thereafter.

      (H) SURVIVAL. All agreements, representations and warranties contained in
this Warrant or in any document delivered pursuant hereto shall be for the
benefit of Warrantholder and shall survive the execution and delivery of this
Warrant and the expiration or other termination of this Warrant.

      (I) GOVERNING LAW. This Warrant shall be governed by, and construed and
enforced in accordance with, the laws of the State of Delaware, excluding
conflict of laws principles that would cause the application of laws of any
other jurisdiction.

      (J) CONSENT TO JURISDICTION AND VENUE. All judicial proceedings arising in
or under or related to this Warrant may be brought in any state or federal court
of competent jurisdiction located in the State of California. By execution and
delivery of this Warrant, each party hereto generally and unconditionally: (a)
consents to personal jurisdiction in Santa Clara County, California; (b) waives
any objection as to jurisdiction or venue in Santa Clara County, California; (c)
agrees not to assert any defense based on lack of jurisdiction or venue in the
aforesaid courts; and (d) irrevocably agrees to be bound by any judgment
rendered thereby in connection with this Warrant. Service of process on any
party hereto in any action arising out of or relating to this Warrant shall be
effective if given in accordance with the requirements for notice set forth in
Section 12(g), and shall be deemed effective and received as set forth in
Section 12(g). Nothing herein shall affect the right to serve process in any
other manner permitted by law or shall limit the right of either party to bring
proceedings in the courts of any other jurisdiction.

      (K) MUTUAL WAIVER OF JURY TRIAL. Because disputes arising in connection
with complex financial transactions are most quickly and economically resolved
by an experienced and expert person and the parties wish applicable state and
federal laws to apply (rather than arbitration rules), the parties desire that
their disputes be resolved by a judge applying such applicable laws. EACH OF THE
COMPANY AND WARRANTHOLDER SPECIFICALLY WAIVES ANY RIGHT IT MAY HAVE TO TRIAL BY
JURY OF ANY CAUSE OF ACTION, CLAIM, CROSS-CLAIM, COUNTERCLAIM, THIRD PARTY CLAIM
OR ANY OTHER CLAIM (COLLECTIVELY, "CLAIMS") ASSERTED BY THE COMPANY AGAINST
WARRANTHOLDER OR ITS ASSIGNEE OR BY WARRANTHOLDER OR ITS ASSIGNEE AGAINST THE
COMPANY. This waiver extends to all such Claims, including Claims that involve
Persons other than Borrower and Lender; Claims that arise out of or are in any
way connected to the relationship between the Company and Warrantholder; and any
Claims for damages, breach of contract, specific performance, or any equitable
or legal relief of any kind, arising out of this Warrant. If this jury waiver is
for any reason unenforceable, all disputes shall be resolved by binding
arbitration conducted under the commercial arbitration rules of the American
Arbitration Association in Palo Alto, California.

      (L) SPECIFIC PERFORMANCE. Warrantholder and Company agree that either may
be irreparably damaged by any breach or threatened breach of this Warrant. Upon
a breach or threatened breach of the terms, covenants and/or conditions of this
Warrant by Warrantholder or Company, the other party shall, in addition to all
other remedies, be entitled to seek a temporary


                                      11.
<PAGE>
or permanent injunction and/or a decree for specific performance, in accordance
with the provisions hereof. Warrantholder and Company each waives the claim or
defense that it has an adequate remedy at law, and such person shall not offer
in any such action or proceeding the claim or defense that such remedy at law
exists.

      (M) COUNTERPARTS. This Warrant and any amendments, waivers, consents or
supplements hereto may be executed in any number of counterparts, and by
different parties hereto in separate counterparts, each of which when so
delivered shall be deemed an original, but all of which counterparts shall
constitute but one and the same instrument.

                  [Remainder of Page Intentionally Left Blank]


                                      12.
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have caused this Warrant to be
executed by its officers thereunto duly authorized as of the Effective Date.

      COMPANY:                   QUATRX PHARMACEUTICALS COMPANY


                                 By: /s/ Robert L. Zerbe
                                    ---------------------------------

                                 Title: CEO
                                       ------------------------------

                                       Attn: Gary Onn, Chief Financial Officer
                                       777 East Eisenhower Parkway, Suite 100
                                       Ann Arbor, MI  48108

      WARRANTHOLDER: HERCULES TECHNOLOGY GROWTH CAPITAL, INC.


                                 By: /s/ Scott Harvey
                                    ---------------------------------

                                 Title: /s/ Chief Legal Officer
                                       ------------------------------

                                       Hercules Technology Growth Capital, Inc.
                                       Attn: Parag Shah
                                       2 Oliver Street, Suite 611
                                       Boston, MA  02110
                                       Facsimile: 617-261-6551
                                       Telephone: 617-261-6552

                                 cc:   Hercules Technology Growth Capital, Inc.
                                       Attn:  Chief Legal Officer
                                       525 University Avenue
                                       Suite 700
                                       Palo Alto, CA  94301
                                       Facsimile: 650-473-9194
                                       Telephone: 650-289-3060


                                      13.
<PAGE>
                                    EXHIBIT I

                               NOTICE OF EXERCISE

To:   Quatrx Pharmaceuticals Company

(1)   The undersigned Warrantholder hereby elects to purchase [       ] shares
      of the Series D Preferred Stock of Quatrx Pharmaceuticals Company,
      pursuant to the terms of the Warrant dated January 26, 2006 (the
      "Warrant") between Quatrx Pharmaceuticals Company and the Warrantholder,
      and [CASH PAYMENT: tenders herewith payment of the Purchase Price in full,
      together with all applicable transfer taxes, if any.] [NET ISSUANCE:
      elects pursuant to Section 3(a) of the Agreement to effect a Net
      Issuance.]

(2)   In exercising its rights to purchase the Series D Preferred Stock of
      Quatrx Pharmaceuticals Company, the undersigned hereby confirms and
      acknowledges the investment representations and warranties made in Section
      10 of the Agreement.

(3)   Please issue a certificate or certificates representing said shares of
      Series D Preferred Stock in the name of the undersigned or in such other
      name as is specified below.


                                         -------------------------------
                                         (Name)

                                         -------------------------------
                                         (Address)


      WARRANTHOLDER:             HERCULES TECHNOLOGY GROWTH CAPITAL, INC.



                                         By:
                                                 -----------------------

                                         Title:
                                                 -----------------------

                                         Date:
                                                 -----------------------



                                      14.
<PAGE>
                                   EXHIBIT II

                           ACKNOWLEDGMENT OF EXERCISE

The undersigned Quatrx Pharmaceuticals Company, hereby acknowledge receipt of
the "Notice of Exercise" from Hercules Technology Growth Capital, Inc., to
purchase [    ] shares of the Series D Preferred Stock of Quatrx Pharmaceuticals
Company, pursuant to the terms of the Agreement, and further acknowledges that
[     ] shares remain subject to purchase under the terms of the Agreement.

      COMPANY:                   QUATRX PHARMACEUTICALS COMPANY


                                 By:
                                    -------------------------------------

                                 Title:
                                       ----------------------------------

                                 Date:
                                      -----------------------------------



                                      15.
<PAGE>
                                   EXHIBIT III

                                 TRANSFER NOTICE

(To transfer or assign the foregoing Agreement execute this form and supply
required information. Do not use this form to purchase shares.)

FOR VALUE RECEIVED, the foregoing Agreement and all rights evidenced thereby are
hereby transferred and assigned to


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(Please Print)


whose address is
                ----------------------------------------------------------------

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                               Dated:
                                    --------------------------------------------

                               Holder's Signature:
                                                  ------------------------------

                               Holder's Address:
                                                --------------------------------

                               -------------------------------------------------


                                      16.