Document:

<PAGE>

                                                                   Exhibit 10.16

                           ESPERION THERAPEUTCS, INC.

               AMENDMENT NO. 3 TO THE INVESTORS' RIGHTS AGREEMENT

     This AMENDMENT NO. 3 TO THE INVESTORS' RIGHTS AGREEMENT (this "Agreement")
is made and entered into as of February 22, 2000, by and among ESPERION
THERAPEUTICS, INC., a Delaware corporation (the "Company"), the Purchasers (as
such term is defined in the Original Agreement defined below), and the
Additional Purchasers set forth on Exhibit 1 attached hereto under the heading
"Additional Purchasers."

     WHEREAS, the Company and the Purchasers are parties to an Investors' Rights
Agreement made and entered into as of July 6, 1998 (the "Original Agreement");
and

     WHEREAS, the Original Agreement was amended as of August 11, 1998 pursuant
to Amendment No. 1 to the Investors' Rights Agreement ("Amendment No. 1"), to
provide for the addition of the Additional Purchasers as Purchasers thereunder
with respect to the issuance of the Series B Shares; and

     WHEREAS, the Original Agreement was amended as of August 11, 1998 pursuant
to Amendment No. 2 to the Investors' Rights Agreement ("Amendment No. 2"), to
provide for the addition of the Additional Purchasers as Purchasers thereunder
with respect to the issuance of the Series C Shares; and

     WHEREAS, the parties to the Original Agreement, as amended, desire to amend
further such agreement, to provide for the addition of the Additional Purchasers
as Purchasers thereunder with respect to the issuance of the Series D Shares,
among other things, on the terms and conditions stated herein and in the
Original Agreement as amended;

     NOW, THEREFORE, in consideration of the mutual promises and covenants set
forth herein, the parties hereto agree as follows:

     1. Defined Terms.
        -------------

       (a) Capitalized terms used and not otherwise defined in this Agreement
shall have the meanings given to such terms in the Original Agreement.

       (b) The following definitions set forth in Section 1 of the Original
Agreement are hereby amended and restated as follows:

       "Preferred Shares" shall mean the Series A Shares, the Series B Shares,
        ----------------
       the Series C Shares and shares of any additional series of preferred
       stock of the Company, the issuance of which is approved by the holders of
       at least 51 % of the Preferred Shares as required by the Restated
       Certificate.
<PAGE>

       "Restated Certificate" shall mean the Company's Amended and Restated
        --------------------
       Certificate of Incorporation, as amended from time to time.

       "Transaction Documents" shall mean, collectively, the Series A Agreement,
        ---------------------
       the Securities Purchase Agreement dated as of August 11, 1998 (the
       "Series B Agreement"), the Securities Purchase Agreement dated as of
       January 7,2000 (the "Series C Agreement"), the Securities Purchase
       Agreement dated as of February 22, 2000 (the "Series D Agreement"), the
       Restated Certificate, this Agreement and the other Ancillary Agreements
       (as defined in the Series A Agreement, the Series B Agreement, the Series
       C Agreement and the Series D Agreement).

        (c)   A new definition is hereby added to Section 1 of the Original
  Agreement, to read in its entirety as follows:

       "Series D Shares" Shall mean the Company's Series D Convertible Preferred
        ---------------
        Stock, par value $0.01 per share.

     2. Exhibit A. Exhibit A to the Original Agreement is amended and restated
        ---------  ---------
in the form of Exhibit A hereto.
               ---------

     3. Request for Registration. Section 1.5(a) of the Original Agreement is
hereby amended (i) to delete the date "January 7,2003" in subsection (A) thereof
and subsitute therefor the date "February 22, 2003," (ii) to amend subsection
(B) after the words "then outstanding Registrable Securities" to read as
Follows:

        other than the Series C and Series D Shares (or any Common Stock issued
        or issuable upon conversion thereof, with respect thereto or in exchange
        therefor) (the "Non-Series C/Non-Series D Initiating Holders") or 30% of
        the then outstanding Registrable Securities consisting of Series C
        Shares and Series D Shares (and any Common Stock issued or issuable upon
        conversion thereof, with respect thereto or in exchange therefor) (the
        "SeriesC/Series D Initating Holders"), and with reference to either or
        both Series C/Series D Initiating Holders and/or the Non-Series C/Non-
        Series D Initiating Holders, the "Initiating Holders" )

     and (iii) to amend and restate subsection (C) thereof to read in its
     entirety as follows:

        (C) After the Company has effected two such registrations pursuant to
        this Section 1.5, one such registration at the request of the
        Non-Series C Initiating Holders and one such registration at the
        request of the Series C Initiating Holders, which registrations have
        been declared or ordered effective and pursuant to which the securities
        have been sold; or

     4. Additional Information and Rights. Section 2.2(a) of the Original
        ---------------------------------
Agreement is hereby amended to add the words "to such Holder" after the word
"issued" therein.

                                       2
<PAGE>

     5. Termination of Financial Information Rights. Section 2.3 of the Original
        -------------------------------------------
Agreement is hereby amended to delete the term "Series C" and substitute
therefor the term "Series D".

     6. Wavier of Antidilution Adjustment. Section 3.6 of the Orginal Agreement
        ---------------------------------
is hereby amended to delete the words "Series A Shares, Series B Shares or
Series C Shares" in subsection (a)(3),(b),(c) and (d) thereof and substitute
therefor the words "Series A Shares, Series B Shares, Series C Shares or Series
D Shares."

     7. Entire Agreement;Amendment; Wavier. Section 4.3 is hereby amended to
        ----------------------------------
amend and restate the proviso at the end of the second sentence thereof to read
in its entirty as follows

        ; provided that no such amendemnt, waiver, discharge or termination may
        amend or modify the provisions of this Section 4.3,amend, modify or
        terminate the amount of the Series Liquidation Value or the Series D
        Liquidation Value (as such terms are defined in the Restated
        Certificate0 or the respective rights of the holders of the Series C
        Share or the Series D Shares relating thereto, or subordinate the rights
        of the holders of the Series C Shares or the Series D Shares to the
        holders of any other class or series of capital stock of the Company in
        existence on the date hereof, in any such case without the prior written
        consent of each holder of the Series C Shares or the Series D Shares,
        respectively.

     8. Joinder. The Additional Purchasers hereby agree to be bound by and
        -------
subject to the terms and conditions of the Original Agreement and the parties
hereto agree that the Additional Purchasers shall be entitled to all of the
rights and benefits of the Purchasers under the Original Agreement.

     9. Governing Law. This Agreement shall be governed in all respects by the
        -------------
laws of the State of Delaware, as applied to agreements among Delaware residents
entered into and to be performed entirely within Delaware.

    10. Effective Date. In accordance with the terms of the Original Agreement,
        --------------
this Agreement will become effective upon execution by the Company and the
holders of at least fifty one percent (51 %) of the Preferred Shares.

    11. Counterparts. This Agreement may be executed in any number of
        ------------
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

                                       3
<PAGE>

        IN WITNESS WHEREOF, the parties hereto have executed this Investors'
Rights Agreement effective as of the day and year first above written.

THE COMPANY:                            ESPERION THERAPEUTICS, INC.

                                        By: /s/ Roger S. Newton
                                           -----------------------------------
                                           Name:  Roger S. Newton
                                           Title: President & CEO

THE PURCHASERS:                         CANAAN EQUITY II L.P.

                                        By:     Canaan Equity Partners II LLC,
                                                Its General Partner

                                        By: /s/  Guy M. Russo
                                           -----------------------------------
                                               Name:  Guy M. Russo
                                               Title: Member/Manager

                                        CANAAN EQUITY II L.P. (QP)

                                        By:   Canaan Equity Partners II LLC,
                                              Its General Partner

                                        By: /s/ Guy M. Russo
                                           -----------------------------------
                                              Name:  Guy M. Russo
                                              Title: Member/Manager

                                        CANAAN EQUITY II ENTREPRENEURS LLC

                                        By:   Canaan Equity Patners II LLC,
                                              Its Manager

                                        By:   /s/ Guy M. Russo
                                              --------------------------------
                                              Name:  Guy M.Russo
                                              Title: Member/Manager

                                       4
<PAGE>

                                         TL VENTURES III L.P.

                                    By:  TL Ventures III Mangement L.P.,
                                         its general partner

                                    By:  TL Ventures III LLC,
                                         its general partner

                                    By:  /s/ Christopher Moller
                                        --------------------------
                                         Name: Christopher Moller
                                         Title: Managing Director

                                    TL VENTURES III OFFSHORE L.P.

                                    By:  TL Ventures III offshore Partners L.P.,
                                         its general partner

                                    By:  TL Ventures III offshore Ltd.,
                                         its general partner

                                    By:  /s/ Christopher Moller
                                        --------------------------
                                         Name: Christopher Moller
                                         Title: Vice President

                                    TL VENTURES III INTERFUND L.P.

                                    By:  TL Ventures III LLC,
                                         its general partner

                                    By:  /s/ Christopher Moller
                                        --------------------------
                                         Name: Christopher Moller
                                         Title: Managing Director

                                    TL VENTURES IV L.P.

                                    By:  TL Ventures IV Management L.P.,
                                         its general partner

                                    By:  /s/ Christopher Moller
                                        -------------------------
                                         Name: Christopher Moller
                                         Title: Managing Director

                                       5
<PAGE>

                                    TL VENTURES IV INTERFUND L.P.

                                    By:  TL Ventures IV LLC,
                                         its general partner

                                    By:  /s/ Christopher Moller
                                         ------------------------
                                         Name: Christopher Mollen
                                         Title: Managing Director

                                    OAK INVESTMENTS PARTNERS VII, LIMITED
                                    PARTNERSHIP

                                    By:  OAK ASSOCIATES VII,LLC
                                         its general partner

                                    By:  __________________________
                                         A Member

                                    OAK VII AFFILIATES FUND, LIMITED
                                    PARTNERSHIP

                                    By:  OAK VII AFFILIATES, LLC
                                         its general partner

                                    By:  __________________________
                                         A Member

                                    AVALON TECHNOLOGY

                                    By:  /s/ [ILLEGIBLE]
                                         --------------------------
                                         A Member

                                       6
<PAGE>

                                    By: /s/ [ILLEGIBLE]
                                        ----------------------------
                                         A Member

                                    OAK VII AFFILIATES FUND, LIMITED
                                    PARTNERSHIP

                                    By:  OAK VII AFFILIATES, LLC
                                         Its General Partner

                                    By:  /s/ [ILLEGIBLE]
                                        ----------------------------
                                         A Member

                                    AVALON INVESTMENTS

                                    By: _______________________________
                                        A Member

                                    HEALTHCAP KB

                                    By: HealthCap AB
                                        its general partner

                                    By: /s/ Magnus Persson
                                        -------------------------------
                                        Magnus Persson
                                        Director

                                    By: /s/ Staffan Lindstrand
                                        -------------------------------
                                        Staffan Lindstrand
                                        Director

<PAGE>

                                    HEALTHCAP COINVEST KB

                                    By:   HealthCap AB
                                          its general partner

                                    By: /s/ Magnus Persson
                                        --------------------------
                                        Magnus Persson
                                        Director

                                    By: /s/ Staffan Lindstrand
                                        --------------------------
                                        Staffan Lindstrand
                                        Director

                                    __________________________
                                    Cesare Sirtori, M.D.

                                    SERVENTIA SA

                                    By: _______________________________________
                                        Franceso Ghiolidi as Sole Administrator

                                    Bioinventor Foundation

                                    By: /s/ Lennart Philipson
                                        --------------------------
                                        Lennart Philipsson
                                        as President

                                    Roger Newton, Ph.D.
<PAGE>

                                    ________________________________
                                    Lennart Philipson

                                    /s/ Roger Newton
                                    ________________________________
                                    Roger Newton, Ph.D.

                                    SCHEER INVESTMENT HOLDINGS II, L.L.C.

                                    By: /s/ David I. Scheer
                                        ----------------------------
                                        David I. Scheer
                                        Managing Member

                                    /s/ Anders Wiklund
                                    --------------------------------
                                    Anders Wiklund

                                    /s/ Sandip Mukherjee, M.D.
                                    --------------------------------
                                    Sandip Mukherjee, M.D.

                                    _________________________________
                                    Seth A. Rudnick

                                    NOVARE KAPTIAL AB

                                    By: _____________________________
                                        Staffan Josephson
                                        Senior Investment Manger

                                       8
<PAGE>

                                    Roger Newton, Ph.D.

                                    SCHEER INVWESTMENT HOLDINGS II, L.L.C.

                                    By:
                                       ------------------------------------
                                       David I. Scheer, Managing Member

                                    Anders Wiklund

                                    Sandip Mukherjee, M.D.

                                    ---------------------------------------
                                    Seth A. Rudnick

                                    NOVARE KAPITAL AB

                                    By: /s/ Staffan Josephson
                                       ------------------------------------
                                       Staffan Josephson, Senior Investment
                                         Manager

                                    LAGRUMMET 621 AB (Reg no 556579-4152)

                                    By: /s/ Pontus Ekman
                                       ------------------------------------
                                       Pontus Ekman
<PAGE>

                                                                       EXHIBIT A

                                  PURCHASERS
                                  ----------

                             TL Ventures III L.P.

                         TL Ventures III Offshore L.P.

                        TL Ventures III Interfund L.P.

                       Oak Investment Partners VII, L.P.

                         Oak VII Affiliates Fund, L.P.

                     Scheer Investment Holdings II, L.L.C.

                       ADDITIONAL PURCHASERS (SERIES B)
                       --------------------------------

                                 HealthCap KB

                              Health CoInvest KB

                             Cesare Sirtori, M.D.

                       ADDITIONAL PURCHASERS (SERIES C)
                       --------------------------------

                             Canaan Equity II L.P.

                          Canaan Equity II L.P. (QP)

                      Canaan Equity II Entrepreneurs LLC

                                Seth A. Rudnick

                              TL Ventures IV L.P.

                         TL Ventures IV Interfund L.P.

                                 Serventia SA

                              Avalon Investments

                              Lennart Philipsson

                              Roger Newton, Ph.D.

                                Anders Wiklund

                                       9
<PAGE>

                            Sandip Mukherjee, M.D.

                       ADDITIONAL PURCHASERS (SERIES D)
                       --------------------------------

                               Novare Kapital AB

                                 Lagrummet 621

                                      10<PAGE>

                                                                   EXHIBIT 10.17

                      RESTRICTED STOCK PURCHASE AGREEMENT
                      -----------------------------------

        THIS RESTRICTED STOCK PURCHASE AGREEMENT (this "Agreement") is dated as
                                                        ---------
of the 6th day of July, 1998, by and between Esperion Therapeutics, Inc., a
Delaware corporation (the "Corporation"), and Roger Newton, Ph.D. ("Employee").
                           -----------                              --------

                             W I T N E S S E T H:
                             - - - - - - - - - -

        WHEREAS, Employee is currently the Senior Director of Preclinical
Discovery and Development of the Corporation; and

        WHEREAS, Employee wishes to purchase, and the Corporation wishes to sell
to Employee, 800,000 shares of the Corporation's common stock, $.001 par value
per share ("Common Stock") at a price of $.001 per share (the "Original Cost Per
            ------------                                       -----------------
Share"); and
-----

        WHEREAS, such shares of Common Stock will be issued to Employee in order
to provide an incentive to Employee to exercise his best efforts on behalf of,
and to remain as an employee of, the Corporation, subject to the terms and
provisions of this Agreement.

        NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties do hereby agree as
follows:

        SECTION 1. Definitions.
                   ------------

        As used in this Agreement, the following terms shall have the following
respective meanings:

        "Cause" shall mean any reason materially and adversely affecting the
         -----
best interests of the Corporation or any of its affiliates or such as to make it
unreasonable to expect the Corporation to continue to employ the Employee,
including, without limitation, the conviction of any crime, the commission or
attempted commission of any act of willful misconduct or dishonesty, malfeasance
or negligence, the failure or neglect by the Employee to perform his or her
duties hereunder or under any other agreement with the Corporation or the
violation or attempted violation of any provision hereof or thereof.

        "Common Shares" shall mean the issued and outstanding shares of the
         -------------
Corporation's Common Stock, at the applicable time.

        "Equity Stock" shall have the meaning set forth in Rule 3a11-1 under the
         ------------
Securities Exchange Act of 1934, as amended, and any successor statute and the
rules and regulations thereunder, as shall be in effect from time to time.

        "Family" shall include any spouse, lineal ancestor or descendant or
         ------
sibling, any trust for the exclusive benefit of any of the foregoing or any
corporation, limited partnership, limited liability company or other entity
majority controlled by any of the foregoing individuals or trusts.

<PAGE>

        "Group" shall mean as to (a) a partnership, any or all of its general or
         -----
limited partners or any "affiliate" thereof (as defined by Rule 405 promulgated
under the Securities Act), (b) a trust, any of the beneficiaries, settlers or
grantors now existing or hereafter arising of, or any Person under common
control with, such trust, (c) a corporation, any of its stockholders, any
subsidiary of such corporation or any corporation which is under common control
with such corporation, or any directors, officers or employees of such
corporation, and (d) a limited liability company, any of its members.

        "New Securities" shall mean any Equity Stock, including, but not limited
         --------------
to, shares of Common Stock, any security which is convertible into or
exercisable or exchangeable for Common Stock, or any right, option or warrant to
acquire any Common Stock of the Corporation.

        "Person" shall mean and include a natural person, a corporation, a
         ------
limited liability company, a partnership, a trust an unincorporated organization
and a government or any department, agency or political subdivision thereof.

        "Preferred Shares" shall mean the Corporation's outstanding Convertible
         ----------------
Participating Preferred Stock (without regard to Series), and any Common Stock
acquired upon conversion thereof.

        "Public Offering" shall mean a distribution of New Securities in an
         ---------------
underwritten public offering to the general public pursuant to a registration
statement filed with and declared effective by the Securities and Exchange
Commission pursuant to the Securities Act.

        "Securities Act" shall mean the Securities Act of 1933, as amended, and
         --------------
any successor statute and the rules and regulations of the Securities and
Exchange Commission thereunder, as shall be in effect at the applicable time.

        "Shares" shall mean the shares of Common Stock purchased by Employee
         ------
hereunder.

        "Termination of Employment" shall mean the termination of the employment
         -------------------------
relationship between the Corporation and Employee for any reason (with or
without cause).

        "Transfer" shall include any direct or indirect sale, assignment,
         --------
transfer, pledge (but not including a pledge in favor of the Corporation),
hypothecation or other disposition of any Shares or of any legal or beneficial
interest therein.

        SECTION 2. Sale to Employee of Common Stock. Subject to the terms and
                   --------------------------------
conditions contained herein, the Corporation hereby sells, transfers and assigns
to Employee, and Employee hereby purchases from the Corporation, the Shares. The
Corporation hereby acknowledges receipt from Employee of payment of the Original
Cost Per Share (or US$80 in the aggregate). Employee covenants and agrees to
forward to the Corporation, if, as and when filed, a copy of any forms filed by
Employee with the Internal Revenue Service with respect to the Shares pursuant
to Section 83(b) of the Internal Revenue Code of 1986, as amended.

                                       2

<PAGE>

Section 3. Termination of Employment
           -------------------------

(a)  (i)   In the event of the Termination of Employment of Employee, the
Corporation shall have the right to purchase from Employee, and if the
Corporation exercises its option pursuant to this Section 3, Employee shall sell
to the Corporation upon the exercise of such right, up to the number of Shares
(rounded up to the nearest whole Share) at the Original Cost Per Share
determined in accordance with the following table:

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
If the Termination of Employment Occurs on or prior to the       Percentage of Shares Subject to Repurchase at Original Cost Per
Following Dates                                                  Share
====================================================================================================================================
<S>                                                              <C>
End of 1st quarter year 1 from date of employment                100%
End of 2nd quarter year 1 from date of employment                93.75%
End of 3rd quarter year 1 from date of employment                87.5%
End of 4th quarter year 1 from date of employment                81.25%
End of 1st quarter year 2 from date of employment                75%
End of 2nd quarter year 2 from date of employment                68.75%
End of 3rd quarter year 2 from date of employment                62.5%
End of 4th quarter year 2 from date of employment                56.25%
End of 1st quarter year 3 from date of employment                50%
End of 2nd quarter year 3 from date of employment                43.75%
End of 3rd quarter year 3 from date of employment                37.5%
End of 4th quarter year 3 from date of employment                31.25%
End of 1st quarter year 4 from date of employment                25%
End of 2nd quarter year 4 from date of employment                18.75%
End of 3rd quarter year 4 from date of employment                12.5%
End of 4th quarter year 4 from date of employment                6.25%
After of 1st quarter year 4 from date of employment              0%
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>

     (ii)  Notwithstanding the foregoing, in the event of the Termination of
Employment of Employee by the Corporation for any reason other than Cause on or
prior to the one (1) Year anniversary from the date of employment, the
percentage of Shares subject to repurchase at Original Cost per Share shall be
75%.

     (iii) The number of Shares subject to purchase pursuant to this Section
3(a) shall be adjusted to give effect to any stock dividend, or other
distribution of stock made on or in respect of such Shares, or any subdivision,
combination or reclassification of the outstanding capital stock of the
Corporation or received in exchange for the Shares.

                                       3

<PAGE>

        (b)   In order to exercise the option to purchase Employee's Shares
under this Section 3, the Corporation shall deliver a written notice to Employee
(the "Repurchase Notice"), indicating its election to purchase the Shares and
      -----------------
specifying the number of Shares which the Corporation elects to purchase and the
purchase price therfor, within 90 days after Employee's Termination of
Employment.

        (c)   The repurchase of Shares hereunder shall be made on a date within
thirty (30) days of the delivery of the Repurchase Notice, by delivery of
payment to the Employee, by check or wire transfer, against receipt of one or
more certificates, properly endorsed, evidencing the Employee's Shares to be so
purchased. If the repurchase is not consummated by such date, the Corporation
may deliver to Employee by check or wire transfer the applicable repurchase
price for the Shares to be repurchased and may cancel the certificates
evidencing such Shares on the books and records of the Corporation.

        SECTION 4.   Legend on Shares and Notice of Transfer.
                     ---------------------------------------

              4.1    Restrictive Legends.
                     -------------------

              (a)    Each certificate evidencing Shares, and each certificate
evidencing Shares held by subsequent transferees of any such certificate, shall
(unless otherwise permitted by the provisions of Section 4.2 hereof) be stamped
or otherwise imprinted with a legend in substantially the following form:

        THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED
        FOR INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
        ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAW. THESE
        SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH
        REGISTRATION OR ANY EXEMPTION THEREFROM UNDER THE SECURITIES ACT
        OF 1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAW.

              (b)    Each certificate evidencing Shares, and each certificate
evidencing Shares held by subsequent transferees of any such certificate, shall
(unless otherwise permitted by the provisions of Section 4.2 hereof) also be
stamped or otherwise imprinted with a legend in substantially the following
form:

        ADDITIONALLY, THE TRANSFER OF THESE SECURITIES IS SUBJECT TO THE
        TERMS AND CONDITIONS OF A RESTRICTED STOCK PURCHASE AGREEMENT
        DATED AS OF _____________, AMONG ESPIRON THERAPEUTICS, INC. AND
        THE HOLDER OF RECORD OF THIS CERTIFICATE AND NO SALE, ASSIGNMENT,
        TRANSFER, PLEDGE, HYPOTHECATION OR OTHER DISPOSITION OF SUCH
        SECURITIES SHALL BE VALID OR EFFECTIVE EXCEPT IN ACCORDANCE WITH
        SUCH AGREEMENT AND UNTIL SUCH TERMS AND CONDITIONS HAVE BEEN
        FULFILLED. COPIES OF SUCH AGREEMENT MAY BE OBTAINED AT NO COST
        BY WRITTEN REQUEST MADE BY THE HOLDER OF RECORD OF THIS CERTIFICATE
        TO THE SECRETARY OF ESPERION THERAPEUTICS, INC.

                                       4

<PAGE>

                  4.2      Notice of Transfer.
                           ------------------

                  (a)      Employee, and any other holder of any Shares by
acceptance thereof, agrees that, prior to any Transfer of any Shares, such
holder will give written notice to the Corporation of such holder's intention to
effect such Transfer and to comply in all other respects with the provisions of
this Section 4.2. Each such notice shall contain (i) a statement setting forth
the intention of said holder's prospective transferee with respect to its
retention or disposition of said Shares; and (ii) unless waived by the
Corporation, a written opinion of counsel for such holder, in form and substance
reasonably satisfactory to the Corporation, as to the necessity or non-necessity
for registration under the Securities Act and applicable state securities laws
in connection with such Transfer and stating the factual and statutory basis
relied upon by counsel. The following provisions shall then apply:

                           (i)  If the proposed Transfer of Shares may be
          effected without registration or qualification under the Securities
          Act and any applicable state securities laws, then the registered
          holder of such Shares shall be entitled to Transfer such Shares in
          accordance with Section 5 hereof and the intended method of
          disposition specified in the statement delivered by such holder to the
          Corporation.

                           (ii)  If the proposed Transfer of such Shares may not
          be effected without registration under the Securities Act or
          registration or qualification under any applicable state securities
          laws, the registered holder of such Shares shall not be entitled to
          Transfer such Shares pursuant to Section 5 hereof until the requisite
          registration or qualification is effective.

                  (b)      Notwithstanding the provisions of Section 4.2(a), in
the case of a Transfer by a holder to a member of such holder's Family, no such
opinion of counsel shall be necessary; provided that the transferee agrees in
                                       --------
writing to be subject to this Agreement to the same extent as if such transferee
were originally a signatory to this Agreement.

                  (c)      Each certificate evidencing the Shares issued upon
such Transfer (and each certificate evidencing any untransferred balance of such
Shares) shall bear the legend set forth in Section 4.1(a) hereof unless (i) in
the written opinion of counsel addressed and delivered and in form and substance
reasonably satisfactory to the Corporation, the registration of future Transfers
is not required by the applicable provisions of the Securities Act or applicable
state securities laws; (ii) the Corporation shall have waived the requirement of
such legend; or (iii) in the opinion of counsel to the Corporation, such
Transfer shall have been made in connection with an effective registration
statement filed pursuant to the Securities Act or in compliance with the
requirements of Rule 144 or Rule 144A (or any similar or successor rule)
promulgated under the Securities Act, and in compliance with applicable state
securities laws.

                  (d)      Each certificate evidencing the Shares issued upon
such Transfer (and each certificate evidencing any untransferred balance of such
Shares) shall bear the legend set forth in Section 4.1(b) hereof, for so long as
this Agreement remains in effect. In the event of the termination of this
Agreement, the holder of Shares may request that the Corporation issue a new
certificate not bearing the legend set forth in Section 4.1(b) hereof.

                                       5
<PAGE>

          SECTION 5.       Covenants of Employee and Corporation.
                           -------------------------------------

                5.1        Prohibited Transfers.
                           --------------------

                  (a)      Employee agrees that he or she shall not Transfer any
of his Shares which are subject to repurchase pursuant to Section 3 above at any
time. Employee further agrees that he shall not Transfer any of his Shares which
are no longer subject to repurchase pursuant to Section 3 above without the
prior written consent of the Board of Directors of the Corporation or the
holders of a majority of the preferred Shares, except as provided for in Section
5.2.

                  (b)      Notwithstanding anything to the contrary contained
herein, Employee (and any permitted transferee of Employee) may Transfer all of
its, his or her Shares: (i) if the stockholder is a limited partnership or a
trust, to any member of the Group of which Employee (or such permitted
transferee) is a member, provided that such transferee shall agree in writing
                         --------
with the Corporation, prior to and as a condition precedent to such Transfer, to
be bound by all of the provisions of this Agreement; (ii) if the stockholder is
a corporation, to any member of its Group; provided that such transferee shall
                                           --------
agree in writing with the Corporation, prior to and as a condition precedent to
such Transfer, to be bound by all of the provisions of this Agreement; (iii) to
any member of the Family of Employee (or such permitted transferee); provided
                                                                     --------
that such transferee shall agree in writing with the Corporation, prior to and
as a condition precedent to such Transfer, to be bound by all of the provisions
of this Agreement and, provided, further, that the interests in any Family
                       -------- -------
trusts shall be non-transferable or, if such interests are transferable, the
Board of Directors of the Corporation shall have granted its consent to such
Transfer in its sole discretion; and (iv) by will or the laws of descent and
distribution, in which event each such transferee shall be bound by all of the
provisions of this Agreement to the same extent as if such transferee were the
deceased Employee (or permitted transferee).

                  (c)      If requested in writing by the managing underwriters,
if any, of any Public Offering, Employee agrees not to offer, sell, contract to
sell or otherwise dispose of any Shares except as part of such Public Offering
within thirty (30) days before or one hundred and eighty (180) days after the
effective date of the registration statement filed with respect to such Public
Offering, and the Corporation hereby also so agrees; provided, however, that
                                                     --------  -------
this restriction will not apply to Transfers permitted under Section 5.1(b),
provided such transferee agrees in writing with the Corporation, prior to and as
--------
a condition precedent to such Transfer, to be bound by the restrictions
contained in this Section 5.1(c) (and the other provisions of this Agreement.)
Notwithstanding the foregoing, in the event that Employee shall have previously
accepted an offer to purchase Offered Shares (as defined below) which have been
offered pursuant to Section 5.2(a), Employee shall not be prohibited from
consummating such sale, provided, that the purchaser agrees to be bound by the
                        --------
restrictions contained in this Section 5.1(c) (and the other provisions of this
Agreement.

          5.2     Right of First and Second Offer on Dispositions.
                  -----------------------------------------------

                  (a)      Except as provided in Section 5.1(b), if Employee
(for purposes of this Section, the "Selling Stockholder") desires to Transfer to
                                    -------------------
any independent third-party all or any part of the Shares, the Selling
Stockholder shall, in the first instance, submit a written offer (the "Offer")
                                                                       -----
to sell such Shares (the "Offered Shares") to the Corporation, which Offer shall
                        --------------
specify the number of Offered Shares proposed to be sold, the total number of
Shares owned by the Selling Stockholder and the terms and conditions, including
price, at which the Shares are being offered to the Corporation.

                                       6
<PAGE>

                  (b)      The Corporation shall have the right to purchase all
or any portion of the Offered Shares on the same terms and conditions specified
in the Offer.

                  (c)      If the Corporation desires to purchase all or any
portion of the Offered Shares, the Corporation shall communicate in writing its
election to purchase (an "Acceptance") to the Selling Stockholder, which
                          ----------
Acceptance shall be delivered in person or mailed to the Selling Stockholder
within 30 days of the date the Offer was made.

                  (d)      If, at the expiration of the 30-day period referred
to in paragraph (c) of this Section or sooner, the Corporation does not elect to
purchase all of the Offered Shares, then the Offered Shares not accepted by the
Corporation for purchase shall be offered (the "Second Offer"), in the second
                                                ------------
instance, to the holders of Preferred Shares (the "Preferred Stockholders").
                                                   ----------------------
Such Second Offer shall be submitted in writing to each Preferred Stockholder,
which offer shall specify the number of Offered Shares proposed to be sold, the
total number of Shares owned by the Selling Stockholder and the terms and
conditions, including price, at which the Offered Shares are being offered to
each of the Preferred Stockholders. The Second Offer shall remain open and
irrevocable for a period of fifteen (15) days (the "Second Acceptance Period")
                                                    ------------------------
from the date of its delivery.

                  (e)      Subject to Section 5.2(g) hereof, each Preferred
Stockholder may accept the Second Offer by delivering to the Selling Stockholder
a notice within the Second Acceptance Period, which notice shall state the
number (the "Accepted Shares") of Offered Shares such Preferred Stockholder
             ---------------
desires to purchase. If the sum of the number of Offered Shares proposed to be
purchased, by the Corporation and all Accepted Shares exceeds the number of
Offered Shares, the Offered Shares shall be allocated among the Preferred
Stockholders that delivered such notice pro rata in accordance with their
                                        --------
Proportionate Percentages; provided, however, that each Preferred Stockholder
                           --------  -------
shall not be required to purchase more than its Accepted Shares and such
purchase shall be on the same terms as those available to any proposed third
party purchaser pursuant to this Section 5.2. For the purposes of this Section
5.2, "Proportionate Percentages" shall mean the pro rata percentage, as to each
      -------------------------                 --------
Preferred Stockholder, equal to the percentage figure which expresses the ratio
between the number of shares of outstanding capital stock of the Corporation
(calculated on an as converted basis) owned by such Preferred Stockholder and
the aggregate number of shares of outstanding capital stock of the Corporation
(calculated on an as converted basis) owned by all Preferred Stockholders.

                  (f)      If the Company elects to purchase all of the Offered
Shares, sale of the Offered Shares to be so purchased pursuant to this Section
shall be made at the offices of the Company on the 45th day following the
delivery of the Acceptance pursuant to paragraph (c) of this Section (or if such
45th day is not a business day, then on the next succeeding business day). If
the Company and Preferred Stockholders elect to purchase all of the Offered
Shares, or the Company declines and the Preferred Stockholders elect to purchase
all of the Offered Shares, sale of the Offered Shares to be so purchased
pursuant to this Section shall be made at the offices of the Company on the 45th
day following the Second Acceptance Notice (or if such 45th day is not a
business day, then on the next succeeding business day). Such sales shall be
effected by the Selling Stockholder's delivery to the Company and/or Preferred
Stockholders of a certificate or certificates evidencing the Offered Shares to
be purchased by it or them, duly endorsed for transfer to the Company and/or the
Preferred Stockholders, which Offered Shares shall be delivered free and clear
of all liens, charges, claims and encumbrances of any nature whatsoever, against
payment to the Selling Stockholder of the purchase price therefor. Payment for
the Offered Shares shall be made as provided in the Offer and/or Second Offer or
by wire transfer or certified check

                                       7
<PAGE>

                  (g)      If the number of Offered Shares exceeds the sum of
those Offered Shares with respect to which the Corporation and the Preferred
Stockholders exercised their rights under this Section 5.2, the Second Offer
shall be deemed to be withdrawn and the Selling Stockholder may transfer the
Offered Shares on the terms, conditions and purchase price specified in the
Offer and the Second Offer to an independent third party purchaser within ninety
(90) days after expiration of the Second Acceptance period, so long as such
third party purchaser (and any subsequent purchaser or transferee) agrees in
writing to be subject to all the terms of this Agreement. Any Offered Shares not
sold within such 90-day period shall continue to be subject to the restrictions
provided for in this Section 5.

         5.3      Drag Along. Subject to Section 5.2 above, anything in this
                  ----------
Agreement to the contrary notwithstanding, in the event that (i) the Board of
Directors of the Corporation by unanimous vote or unanimous written consent
and/or the holders of at least a majority of the then outstanding Preferred
Shares by vote or written consent approves a transaction pursuant to which any
Person or Persons not affiliated with any of the Preferred Stockholders will
acquire 50% or more of the Common Shares of the Corporation (by stock purchase,
merger or otherwise) or all or substantially all of the assets of the
Corporation, upon the written request of the holders of at least a majority of
the Preferred Shares, Employee agrees to offer to sell all of his or her Shares,
and to sell all of his or her Shares, to such Person or Persons or to vote all
of his or her Shares in favor of the sale of assets, as the case may be, in
either case upon the terms and conditions of the transaction approved by the
Board of Directors of the Corporation and/or the holders of at least a majority
of the Preferred Shares; provided, however, that employee's obligation to sell
                         --------  -------
his or her Shares pursuant to this Section 5.3 shall only apply if all the
Shares are sold on the same financial terms and conditions.

         5.4      Co-Sale Rights: Voting and Board Provisions. Employee agrees
                  -------------------------------------------
to be bound by the Co-Sale Rights and Voting and Board Provisions contained in
Sections 2(d) and 4 of that certain Stockholders' Agreement dated 6 July 1998 by
                                                                  -----------
and among the Corporation and the parties thereto (the "Stockholders'
                                                        -------------
Agreement"). Employee shall execute the Stockholders' Agreement for the limited
---------
purpose of being bound by Sections 2(d) and 4 thereto.

         SECTION 6. Representations.
                    ---------------

         6.1      Representations of Employee. In connection with Employee's
                  ---------------------------
purchase of the Shares, Employee hereby represents and warrants to the
Corporation as follows:

                  (a)      Investment Intent: Capacity to Protect Interests.
                           ------------------------------------------------
Employee is purchasing the Shares solely for his or her own account for
investment and not with a view to or for sale in connection with any
distribution of the Shares or any portion thereof and not with any present
intention of selling, offering to sell or otherwise disposing of or distributing
the Shares or any portion thereof in any transaction other than a transaction
exempt from registration under the Securities Act. Employee also represents that
the entire legal and beneficial interest of the Shares is being purchased, and
will be held, for his or her account only, and neither in whole or in part for
any other person.

                   (b)     Restricted Securities. Employee understands and
                           ---------------------
acknowledges that the sale of the Shares has not been registered under the
Securities Act; that the Shares must be held indefinitely unless subsequently
registered under the Securities Act or an exemption from such registration is
available; and that the Corporation is under no obligation to register the
Shares.

                                       8
<PAGE>

                   (c)     Disposition under Rule 144. Employee understands that
                           --------------------------
the Shares are restricted securities within the meaning of Rule 144 promulgated
under the Securities Act; that the exemption from registration under Rule 144
will not be available in any event for at least two years from the date of
purchase of any payment for the Shares, and even then will not be available
unless (i) a public trading market then exists for the Shares, (ii) adequate
information concerning the Corporation is then available to the public, and
(iii) other terms and conditions of Rule 144 are complied with; and that any
sale of the shares may be made only in limited amounts in accordance with such
terms and conditions.

         6.2       Representations of the Corporation. The Corporation
                   ----------------------------------
represents to Employee that:

                   (a)     The execution, delivery and performance by the
Corporation of this Agreement and all transactions contemplated by this
Agreement have been duly authorized by all action required by law, its
Certificate of Incorporation, its Bylaws or otherwise.

                   (b)     This Agreement has been duly executed and delivered
by the Corporation and constitutes the legal, valid and binding obligation of
the Corporation enforceable against it in accordance with its terms.

          SECTION 7.       Withholding. Upon the request of the Corporation,
                           -----------
Employee shall promptly pay to the Corporation, or make arrangements
satisfactory to the Corporation regarding payment of, any Federal, state or
local taxes of any kind required by law to be withheld with respect to the
Shares (or any distributions of other securities or property (including cash)
thereon or issued in replacement thereof).

          SECTION 8.       Remedies. In case any one or more of the covenants
                           --------
and/or agreements set forth in this Agreement shall have been breached by any
party hereto, the party entitled to the benefit of such covenants or agreements
may proceed to protect and enforce its rights either by suit in equity and/or by
action at law, including, but not limited to, (a) an action for damages as a
result of any such breach, (b) an action for specific performance of any such
covenant or agreement contained in this Agreement, and/or (c) a temporary or
permanent injunction, in any case without showing any actual damage. The rights,
power and remedies of the parties under this Agreement are cumulative and not
exclusive of any other agreement or law. No single or partial assertion or
exercise of any right, power or remedy of a party hereunder shall preclude any
other or further assertion or exercise thereof. Any purported Transfer in
violation of the provisions of this Agreement shall be null and void ab initjo.
                                                                     -- ------

          SECTION 9.       Successors and Assigns. Except as otherwise expressly
                           ----------------------
provided herein, this Agreement shall bind and inure to the benefit of the
Corporation, Employee, the respective successors or heirs, distributees and
personal representatives and permitted assigns of the Corporation and Employee,
and each other person who shall properly become a registered holder of any
Shares that have not theretofore been sold to the public pursuant to a
registration statement under the Securities Act or Rule 144 or Rule 144A (or any
similar or successor rule).

          SECTION 10.      Entire Agreement. This Agreement contains the entire
                           ----------------
agreement among the parties with respect to the subject matter hereof and
supersedes other prior and contemporaneous arrangements or understandings with
respect thereto.

                                       9
<PAGE>

          SECTION 11.      Notices. All notices, consents and other
                           -------
communications under this Agreement shall be in writing and shall be deemed to
have been duly given (a) when delivered by hand, (b) one (1) business day after
the business day of transmission, if sent by telex or telecopier (with receipt
confirmed), provided that a copy is mailed by registered mail, return receipt
            --------
requested, or (c) one (1) business day after the business day of deposit with
the carrier, if sent by Express Mail, Federal Express or other express delivery
service (receipt requested), in each case to the appropriate addresses, telex
numbers and telecopier numbers set forth below (or to such other addresses or
telecopy numbers as a party may designate as to itself by notice to the other
parties):

          (a)   If to Employee:

                           Roger Newton, Ph.D.
                           1425 Bardstown Trail
                           Ann Arbor, MI 48105
                           Telecopier No.:

          (b)   If to the Corporation:

                           Esperion Therapeutics, Inc.
                           3621 S. State Street, 695 KMS Place
                           Ann Arbor, Michigan 48108
                           Telecopier No.: (734) 332-0516
                           Attention: Roger Newton. Ph.D.

                with a copy to:

                           Sills Cummis Zuckerman Radin
                           Tischman Epstein & Gross, P.A.
                           One Riverfront Plaza
                           Newark, New Jersey 07102
                           Telecopier No.: (973) 643-6500
                           Attention:   Ira A. Rosenberg, Esq.

          SECTION 12.      Changes. The terms and provisions of this Agreement
                           -------
may not be modified or amended, or any of the provisions hereof waived,
temporarily or permanently, without the prior written consent of each of the
parties hereto.

          SECTION 13.      Counterparts. This Agreement may be executed in any
                           ------------
number of counterparts, and each such counterpart shall be deemed to be an
original instrument, but all such counterparts together shall constitute but one
agreement.

          SECTION 14.      Headings. The benefits of the various sections of
                           --------
this Agreements have been inserted for convenience of reference only and shall
not be deemed to be part of this Agreement.

                                      10
<PAGE>

          SECTION 15.      Nouns and Pronouns. Whenever the context may require,
                           ------------------
any pronouns used herein shall include the corresponding masculine feminine or
neuter forms, and the singular form of names and pronouns shall include the
plural and vice-versa.

          SECTION 16.      Severability. Any provision of this Agreement that is
                           ------------
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability. Such
prohibition or unenforceability in any one jurisdiction shall not invalidate or
render unenforceable such provision in any other jurisdiction.

          SECTION 17.      Governing Law. This Agreement and (unless otherwise
                           -------------
provided) all amendments hereof and waivers and consents hereunder shall be
governed by the internal law of the State of Delaware, without regard to the
conflicts of law principles thereof.

          IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date and year first written above.

WITNESS                      ESPERION THERAPEUTICS, INC.

/s/ [ILLEGIBLE]              By:
----------------------          ----------------------------
                             Name:
                             Title:

WITNESS

/s/ Michael E. Pape          /s/ Roger Newton, Ph.D.
----------------------       -------------------------------
                             Name: Roger Newton, Ph.D.

                                      11

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