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Exhibit 10.23    
    

 
 

OPTIMER PHARMACEUTICALS, INC.
  2006 EQUITY INCENTIVE PLAN    
    

        1.    Purposes of the Plan.    The purposes of this Plan are: 

	•
	to
attract and retain the best available personnel for positions of substantial responsibility,

	•
	to
provide additional incentive to Employees, Directors and Consultants, and

	•
	to
promote the success of the Company's business. 

        The
Plan permits the grant of Incentive Stock Options, Nonstatutory Stock Options, Restricted Stock, Restricted Stock Units, Stock Appreciation Rights, Performance Units and Performance
Shares. 

        2.    Definitions.    As used herein, the following definitions will apply: 

        (a)   "Administrator" means the Board or any of its Committees as will be administering the Plan, in accordance with
Section 4 of the Plan. 

        (b)   "Applicable Laws" means the requirements relating to the administration of equity-based awards under U.S. state
corporate laws, U.S. federal and state securities laws, the Code, any stock exchange or quotation system on which the Common Stock is listed or quoted and the applicable laws of any foreign
country or jurisdiction where Awards are, or will be, granted under the Plan. 

        (c)   "Award" means, individually or collectively, a grant under the Plan of Options, SARs, Restricted Stock, Restricted Stock
Units, Performance Units or Performance Shares. 

        (d)   "Award Agreement" means the written or electronic agreement setting forth the terms and provisions applicable to each
Award granted under the Plan. The Award Agreement is subject to the terms and conditions of the Plan. 

        (e)   "Board" means the Board of Directors of the Company. 

        (f)    "Change in Control" means the occurrence of any of the following events: 

          (i)  Any
"person" (as such term is used in Sections 13(d) and 14(d) of the Exchange Act) becomes the "beneficial owner" (as defined in
Rule 13d-3 of the Exchange Act), directly or indirectly, of securities of the Company representing fifty percent (50%) or more of the total voting power represented by the Company's
then outstanding voting securities; or 

         (ii)  The
consummation of the sale or disposition by the Company of all or substantially all of the Company's assets; 

        (iii)  A
change in the composition of the Board occurring within a two-year period, as a result of which fewer than a majority of the directors are Incumbent
Directors. "Incumbent Directors" means directors who either (A) are Directors as of the effective date of the Plan, or (B) are elected, or nominated for election, to the Board with the
affirmative votes of at least a majority of the Incumbent Directors at the time of such election or nomination (but will not include an individual whose election or nomination is in connection
with an actual or threatened proxy contest relating to the election of directors to the Company); or 

        (iv)  The
consummation of a merger or consolidation of the Company with any other corporation, other than a merger or consolidation which would result in the voting
securities of the Company outstanding immediately prior thereto continuing to represent (either by remaining outstanding or by being converted into voting securities of the surviving entity or its
parent) at least fifty percent (50%) of the total voting power represented by the voting securities of the Company or such surviving entity or its parent outstanding immediately after such merger or
consolidation. 

 

        (g)   "Code" means the Internal Revenue Code of 1986, as amended. Any reference to a section of the Code herein will be a
reference to any successor or amended section of the Code. 

        (h)   "Committee" means a committee of Directors or of other individuals satisfying Applicable Laws appointed by the Board in
accordance with Section 4 hereof. 

        (i)    "Common Stock" means the common stock of the Company. 

        (j)    "Company" means Optimer Pharmaceuticals, Inc., a Delaware corporation, or any successor thereto. 

        (k)   "Consultant" means any person, including an advisor, engaged by the Company or a Parent or Subsidiary to render services
to such entity. 

        (l)    "Director" means a member of the Board. 

        (m)  "Disability" means total and permanent disability as defined in Section 22(e)(3) of the Code, provided that in the
case of Awards other than Incentive Stock Options, the Administrator in its discretion may determine whether a permanent and total disability exists in accordance with uniform and
non-discriminatory standards adopted by the Administrator from time to time. 

        (n)   "Employee" means any person, including Officers and Directors, employed by the Company or any Parent or Subsidiary of the
Company. Neither service as a Director nor payment of a director's fee by the Company will be sufficient to constitute "employment" by the Company. 

        (o)   "Exchange Act" means the Securities Exchange Act of 1934, as amended. 

        (p)   "Exchange Program" means a program under which (i) outstanding Awards are surrendered or cancelled in exchange for
Awards of the same type (which may have lower exercise prices and different terms), Awards of a different type, and/or cash, (ii) Participants would have the opportunity to transfer any
outstanding Awards to a financial institution or other person or entity selected by the Administrator, and/or (iii) the exercise price of an outstanding Award is reduced. The Administrator will
determine the terms and conditions of any Exchange Program in its sole discretion. 

        (q)   "Fair Market Value" means, as of any date, the value of Common Stock determined as follows: 

          (i)  If
the Common Stock is listed on any established stock exchange or a national market system, including without limitation the Nasdaq Global Market or the Nasdaq Capital
Market of The Nasdaq Stock Market, its Fair Market Value will be the closing sales price for such stock (or the closing bid, if no sales were reported) as quoted on such exchange or system on
the day of determination, as reported in The Wall Street Journal or such other source as the Administrator deems reliable; 

         (ii)  If
the Common Stock is regularly quoted by a recognized securities dealer but selling prices are not reported, the Fair Market Value of a Share will be the mean between
the high bid and low asked prices for the Common Stock on the day of determination, as reported in The Wall Street Journal or such other source as the
Administrator deems reliable; 

        (iii)  For
purposes of any Awards granted on the Registration Date, the Fair Market Value will be the initial price to the public as set forth in the final prospectus
included within the registration statement in Form S-1 filed with the Securities and Exchange Commission for the initial public offering of the Company's Common Stock; or 

        (iv)  In
the absence of an established market for the Common Stock, the Fair Market Value will be determined in good faith by the Administrator. 

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        (r)   "Fiscal Year" means the fiscal year of the Company. 

        (s)   "Incentive Stock Option" means an Option intended to qualify as an incentive stock option within the meaning of
Section 422 of the Code and the regulations promulgated thereunder. 

        (t)    "Nonstatutory Stock Option" means an Option that by its terms does not qualify or is not intended to qualify as an
Incentive Stock Option. 

        (u)   "Officer" means a person who is an officer of the Company within the meaning of Section 16 of the Exchange Act and
the rules and regulations promulgated thereunder. 

        (v)   "Option" means a stock option granted pursuant to the Plan. 

        (w)  "Optioned Stock" means the Common Stock subject to an Award. 

        (x)   "Outside Director" means a Director who is not an Employee. 

        (y)   "Parent" means a "parent corporation," whether now or hereafter existing, as defined in Section 424(e) of
the Code. 

        (z)   "Participant" means the holder of an outstanding Award. 

        (aa) "Performance Share" means an Award denominated in Shares which may be earned in whole or in part upon attainment of
performance goals or other vesting criteria as the Administrator may determine pursuant to Section 10. 

        (bb) "Performance Unit" means an Award which may be earned in whole or in part upon attainment of performance goals or other
vesting criteria as the Administrator may determine and which may be settled for cash, Shares or other securities or a combination of the foregoing pursuant to Section 10. 

        (cc) "Period of Restriction" means the period during which the transfer of Shares of Restricted Stock are subject to
restrictions and therefore, the Shares are subject to a substantial risk of forfeiture. Such restrictions may be based on the passage of time, the achievement of target levels of performance, or the
occurrence of other events as determined by the Administrator. 

        (dd) "Plan" means this 2006 Equity Incentive Plan. 

        (ee) "Registration Date" means the effective date of the first registration statement that is filed by the Company and
declared effective pursuant to Section 12(g) of the Exchange Act, with respect to any class of the Company's securities. 

        (ff)  "Restricted Stock" means Shares issued pursuant to a Restricted Stock award under Section 7 of the Plan, or
issued pursuant to the early exercise of an Option. 

        (gg) "Restricted Stock Unit" means a bookkeeping entry representing an amount equal to the Fair Market Value of one Share,
granted pursuant to Section 8. Each Restricted Stock Unit represents an unfunded and unsecured obligation of the Company. 

        (hh) "Rule 16b-3" means Rule 16b-3 of the Exchange Act or any successor to
Rule 16b-3, as in effect when discretion is being exercised with respect to the Plan. 

        (ii)   "Section 16(b)" means Section 16(b) of the Exchange Act. 

        (jj)   "Service Provider" means an Employee, Director or Consultant. 

        (kk) "Share" means a share of the Common Stock, as adjusted in accordance with Section 13 of the Plan. 

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        (ll)   "Stock Appreciation Right" or "SAR" means an Award, granted alone or in
connection with an Option, that pursuant to Section 9 is designated as a SAR. 

        (mm) "Subsidiary" means a "subsidiary corporation", whether now or hereafter existing, as defined in Section 424(f) of
the Code. 

        3.    Stock Subject to the Plan.    

        (a)    Stock Subject to the Plan.    Subject to the provisions of Section 13 of the Plan, the maximum aggregate
number of Shares that may be issued under the Plan is [            ] (which has been determined after adjustment to reflect the stock split which will be completed by the
Company prior to the initial registration of the Company's Common Stock under Section 12 of the Exchange Act). The Shares may be authorized, but unissued, or reacquired Common Stock. 

        (b)    Automatic Share Reserve Increase.    The number of Shares available for issuance under the Plan shall be
increased on the first day of each Fiscal Year beginning with the 2008 Fiscal Year, in an amount equal to the lesser of (A) [            ] Shares (which has been
determined after adjustment to reflect the stock split which will be completed by the Company prior to the initial registration of the Company's Common Stock under Section 12 of the Exchange
Act), (B) five percent (5%) of the outstanding Shares on the last day of the immediately preceding Fiscal Year or (C) such lesser number of Shares determined by the Board. 

        (c)    Lapsed Awards.    If an Award expires or becomes unexercisable without having been exercised in full, is
surrendered pursuant to an Exchange Program, or, with respect to Restricted Stock, Restricted Stock Units, Performance Units or Performance Shares, is forfeited to or repurchased by the Company due to
failure to vest, the unpurchased Shares (or for Awards other than Options or SARs the forfeited or repurchased Shares) which were subject thereto will become available for future grant or sale
under the Plan (unless the Plan has terminated). With respect to SARs, only Shares actually issued pursuant to an SAR will cease to be available under the Plan; all remaining Shares under SARs will
remain available for future grant or sale under the Plan (unless the Plan has terminated). Shares that have actually been issued under the Plan under any Award will not be returned to the Plan and
will not become available for future distribution under the Plan; provided, however, that if Shares issued pursuant to Awards of Restricted Stock, Performance Units or Performance Shares are
repurchased by the Company or are forfeited to the Company, such Shares will become available for future grant under the Plan. Shares used to pay the exercise price of an Award or to satisfy the
minimum statutory withholding obligations related to an Award will become available for future grant or sale under the Plan. Notwithstanding the foregoing and, subject to adjustment as provided in
Section 13, the maximum number of Shares that may be issued upon the exercise of Incentive Stock Options shall equal the aggregate Share number stated in Section 3(a), plus, by that
portion of each automatic increase specified in Section 3(b) that does not exceed [            ] Shares. 

        (d)    Share Reserve.    The Company, during the term of this Plan, will at all times reserve and keep available such
number of Shares as will be sufficient to satisfy the requirements of the Plan. 

        4.    Administration of the Plan.    

        (a)    Procedure.    

        (i)    Multiple Administrative Bodies.    Different Committees with respect to different groups of Service Providers
may administer the Plan. 

        (ii)    Section 162(m).    To the extent that the Administrator determines it to be desirable to qualify
Options granted hereunder as "performance-based compensation" within the meaning of Section 162(m) of the Code, the Plan will be administered by a Committee of two or more "outside directors"
within the meaning of Section 162(m) of the Code. 

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        (iii)    Rule 16b-3.    To the extent desirable to qualify transactions hereunder as exempt under
Rule 16b-3, the transactions contemplated hereunder will be structured to satisfy the requirements for exemption under Rule 16b-3. 

        (iv)    Other Administration.    Other than as provided above, the Plan will be administered by (A) the Board
or (B) a Committee, which committee will be constituted to satisfy Applicable Laws. 

        (b)    Powers of the Administrator.    Subject to the provisions of the Plan, and in the case of a Committee, subject
to the specific duties delegated by the Board to such Committee, the Administrator will have the authority, in its discretion: 

          (i)  to
determine the Fair Market Value; 

         (ii)  to
select the Service Providers to whom Awards may be granted hereunder; 

        (iii)  to
determine the number of Shares to be covered by each Award granted hereunder; 

        (iv)  to
approve forms of Award Agreements for use under the Plan; 

         (v)  to
determine the terms and conditions, not inconsistent with the terms of the Plan, of any Award granted hereunder. Such terms and conditions include, but are not
limited to, the exercise price, the time or times when Awards may be exercised (which may be based on performance criteria), any vesting acceleration or waiver of forfeiture restrictions, and any
restriction or limitation regarding any Award or the Shares relating thereto, based in each case on such factors as the Administrator will determine; 

        (vi)  to
determine the terms and conditions of any, and to institute any Exchange Program; 

       (vii)  to
construe and interpret the terms of the Plan and Awards granted pursuant to the Plan; 

      (viii)  to
prescribe, amend and rescind rules and regulations relating to the Plan, including rules and regulations relating to sub-plans established for the
purpose of satisfying applicable foreign laws; 

        (ix)  to
modify or amend each Award (subject to Section 18(c) of the Plan), including the discretionary authority to extend the post-termination
exercisability period of Awards; 

         (x)  to
allow Participants to satisfy withholding tax obligations in such manner as prescribed in Section 14; 

        (xi)  to
authorize any person to execute on behalf of the Company any instrument required to effect the grant of an Award previously granted by the Administrator; 

       (xii)  to
allow a Participant to defer the receipt of the payment of cash or the delivery of Shares that would otherwise be due to such Participant under an Award; 

      (xiii)  to
make all other determinations deemed necessary or advisable for administering the Plan. 

        (c)    Effect of Administrator's Decision.    The Administrator's decisions, determinations and interpretations will
be final and binding on all Participants and any other holders of Awards. 

        5.    Eligibility.    Nonstatutory Stock Options, Restricted Stock, Restricted Stock Units, SARs, Performance Units
and Performance Shares may be granted to Service Providers. Incentive Stock Options may be granted only to Employees. 

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        6.    Stock Options.    

        (a)    Limitations.    Each Option will be designated in the Award Agreement as either an Incentive Stock Option or a
Nonstatutory Stock Option. However, notwithstanding such designation, to the extent that the aggregate Fair Market Value of the Shares with respect to which Incentive Stock Options are exercisable for
the first time by the Participant during any calendar year (under all plans of the Company and any Parent or Subsidiary) exceeds $100,000, such Options will be treated as Nonstatutory Stock Options.
For purposes of this Section 6(a), Incentive Stock Options will be taken into account in the order in which they were granted. The Fair Market Value of the Shares will be determined as of the
time the Option with respect to such Shares is granted. 

        (b)    Term of Option.    The term of each Option will be stated in the Award Agreement. In the case of an Incentive
Stock Option, the term will be ten (10) years from the date of grant or such shorter term as may be provided in the Award Agreement. Moreover, in the case of an Incentive Stock Option granted
to a Participant who, at the time the Incentive Stock Option is granted, owns stock representing more than ten percent (10%) of the total combined voting power of all classes of stock of the Company
or any Parent or Subsidiary, the term of the Incentive Stock Option will be five (5) years from the date of grant or such shorter term as may be provided in the Award Agreement. 

        (c)    Option Exercise Price and Consideration.    

        (i)    Exercise Price.    The per share exercise price for the Shares to be issued pursuant to exercise of an Option
will be determined by the Administrator, subject to the following: 

        (1)   In
the case of an Incentive Stock Option 

        a)    granted
to an Employee who, at the time the Incentive Stock Option is granted, owns stock representing more than ten percent (10%) of the voting power of all classes of
stock of the Company or any Parent or Subsidiary, the per Share exercise price will be no less than 110% of the Fair Market Value per Share on the date of grant. 

        b)    granted
to any Employee other than an Employee described in paragraph (A) immediately above, the per Share exercise price will be no less than 100% of the Fair
Market Value per Share on the date of grant. 

        c)     Notwithstanding
the foregoing, Incentive Stock Options may be granted with a per Share exercise price of less than 100% of the Fair Market Value per Share on the date of
grant pursuant to a transaction described in, and in a manner consistent with, Section 424(a) of the Code. 

        (2)   In
the case of a Nonstatutory Stock Option, the per Share exercise price will be no less than 100% of the Fair Market Value per Share on the date of grant. 

        (ii)    Waiting Period and Exercise Dates.    At the time an Option is granted, the Administrator will fix the period
within which the Option may be exercised and will determine any conditions that must be satisfied before the Option may be exercised. 

        (iii)    Form of Consideration.    The Administrator will determine the acceptable form of consideration for
exercising an Option, including the method of payment. In the case of an Incentive Stock Option, the Administrator will determine the acceptable form of consideration at the time of grant. Such
consideration may consist entirely of: (1) cash; (2) check; (3) other Shares, provided Shares acquired directly or indirectly from the Company, (A) have been owned by the
Participant and not subject to substantial risk of forfeiture for more than six months on the date of surrender, and (B) have a Fair Market Value on the date of surrender 

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equal
to the aggregate exercise price of the Shares as to which said Option will be exercised; (4) consideration received by the Company under a broker-assisted cashless exercise
program; (5) any combination of the foregoing methods of payment; or (6) such other consideration and method of payment for the issuance of Shares to the extent permitted by
Applicable Laws. 

        (d)    Exercise of Option.    

        (i)    Procedure for Exercise; Rights as a Stockholder.    Any Option granted hereunder will be exercisable according
to the terms of the Plan and at such times and under such conditions as determined by the Administrator and set forth in the Award Agreement. An Option may not be exercised for a fraction of
a Share. 

        An
Option will be deemed exercised when the Company receives: (i) notice of exercise (in such form as the Administrator specify from time to time) from the person entitled
to exercise the Option, and
(ii) full payment for the Shares with respect to which the Option is exercised (together with an applicable withholding taxes). Full payment may consist of any consideration and method of
payment authorized by the Administrator and permitted by the Award Agreement and the Plan. Shares issued upon exercise of an Option will be issued in the name of the Participant or, if requested by
the Participant, in the name of the Participant and his or her spouse. Until the Shares are issued (as evidenced by the appropriate entry on the books of the Company or of a duly authorized
transfer agent of the Company), no right to vote or receive dividends or any other rights as a stockholder will exist with respect to the Optioned Stock, notwithstanding the exercise of the Option.
The Company will issue (or cause to be issued) such Shares promptly after the Option is exercised. No adjustment will be made for a dividend or other right for which the record date is prior to
the date the Shares are issued, except as provided in Section 13 of the Plan. 

        Exercising
an Option in any manner will decrease the number of Shares thereafter available, both for purposes of the Plan and for sale under the Option, by the number of Shares as to
which the Option is exercised. 

        (ii)    Termination of Relationship as a Service Provider.    If a Participant ceases to be a Service Provider, other
than upon the Participant's death or Disability, the Participant may exercise his or her Option within such period of time as is specified in the Award Agreement to the extent that the Option is
vested on the date of termination (but in no event later than the expiration of the term of such Option as set forth in the Award Agreement). In the absence of a specified time in the Award
Agreement, the Option will remain exercisable for three (3) months following the Participant's termination. Unless otherwise provided by the Administrator, if on the date of termination the
Participant is not vested as to his or her entire Option, the Shares covered by the unvested portion of the Option will revert to the Plan. If after termination the Participant does not exercise his
or her Option within the time specified by the Administrator, the Option will terminate, and the Shares covered by such Option will revert to the Plan. 

        (iii)    Disability of Participant.    If a Participant ceases to be a Service Provider as a result of the
Participant's Disability, the Participant may exercise his or her Option within such period of time as is specified in the Award Agreement to the extent the Option is vested on the date of termination
(but in no event later than the expiration of the term of such Option as set forth in the Award Agreement). In the absence of a specified time in the Award Agreement, the Option will remain
exercisable for twelve (12) months following the Participant's termination. Unless otherwise provided by the Administrator, if on the date of termination the Participant is not vested as to his
or her entire Option, the Shares covered by the unvested portion of the Option will revert to the Plan. If after termination the Participant 

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does
not exercise his or her Option within the time specified herein, the Option will terminate, and the Shares covered by such Option will revert to the Plan. 

        (iv)    Death of Participant.    If a Participant dies while a Service Provider, the Option may be exercised following
the Participant's death within such period of time as is specified in the Award Agreement to the extent that the Option is vested on the date of death (but in no event may the option be
exercised later than the expiration of the term of such Option as set forth in the Award Agreement), by the Participant's designated beneficiary, provided such beneficiary has been designated prior to
Participant's death in a form acceptable to the Administrator. If no such beneficiary has been designated by the Participant, then such Option may be exercised by the personal representative of the
Participant's estate or by the person(s) to whom the Option is transferred pursuant to the Participant's will or in accordance with the laws of descent and distribution. In the absence of a specified
time in the Award Agreement, the Option will remain exercisable for twelve (12) months following Participant's death. Unless otherwise provided by the Administrator, if at the time of death
Participant is not vested as to his or her entire Option, the Shares covered by the unvested portion of the Option will immediately revert to the Plan. If the Option is not so exercised within the
time specified herein, the Option will terminate, and the Shares covered by such Option will revert to the Plan. 

        7.    Restricted Stock.    

        (a)    Grant of Restricted Stock.    Subject to the terms and provisions of the Plan, the Administrator, at any time
and from time to time, may grant Shares of Restricted Stock to Service Providers in such amounts as the Administrator, in its sole discretion, will determine. 

        (b)    Restricted Stock Agreement.    Each Award of Restricted Stock will be evidenced by an Award Agreement that will
specify the Period of Restriction, the number of Shares granted, and such other terms and conditions as the Administrator, in its sole discretion, will determine. Unless the Administrator determines
otherwise, the Company as escrow agent will hold Shares of Restricted Stock until the restrictions on such Shares have lapsed. 

        (c)    Transferability.    Except as provided in this Section 7, Shares of Restricted Stock may not be sold,
transferred, pledged, assigned, or otherwise alienated or hypothecated until the end of the applicable Period of Restriction. 

        (d)    Other Restrictions.    The Administrator, in its sole discretion, may impose such other restrictions on Shares
of Restricted Stock as it may deem advisable or appropriate. 

        (e)    Removal of Restrictions.    Except as otherwise provided in this Section 7, Shares of Restricted Stock
covered by each Restricted Stock grant made under the Plan will be released from escrow as soon as practicable after the last day of the Period of Restriction or at such other time as the
Administrator may determine. The Administrator, in its discretion, may accelerate the time at which any restrictions will lapse or be removed. 

        (f)    Voting Rights.    During the Period of Restriction, Service Providers holding Shares of Restricted Stock
granted hereunder may exercise full voting rights with respect to those Shares, unless the Administrator determines otherwise. 

        (g)    Dividends and Other Distributions.    During the Period of Restriction, Service Providers holding Shares of
Restricted Stock will be entitled to receive all dividends and other distributions paid with respect to such Shares unless otherwise provided in the Award Agreement. If any such dividends or
distributions are paid in Shares, the Shares will be subject to the same restrictions on transferability and forfeitability as the Shares of Restricted Stock with respect to which they
were paid. 

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        (h)    Return of Restricted Stock to Company.    On the date set forth in the Award Agreement, the Restricted Stock
for which restrictions have not lapsed will revert to the Company and again will become available for grant under the Plan. 

        8.    Restricted Stock Units.    

        (a)    Grant.    Restricted Stock Units may be granted at any time and from time to time as determined by the
Administrator. After the Administrator determines that it will grant Restricted Stock Units under the Plan, it shall advise the Participant in an Award Agreement of the terms, conditions, and
restrictions related to the grant, including the number of Restricted Stock Units. 

        (b)    Vesting Criteria and Other Terms.    The Administrator shall set vesting criteria in its discretion, which,
depending on the extent to which the criteria are met, will determine the number of Restricted Stock Units that will be paid out to the Participant. The Administrator may set vesting criteria based
upon the achievement of Company-wide, business unit, or individual goals (including, but not limited to, continued employment), or any other basis determined by the Administrator in
its discretion. 

        (c)    Earning Restricted Stock Units.    Upon meeting the applicable vesting criteria, the Participant shall be
entitled to receive a payout as specified in the Restricted Stock Unit Award Agreement. Notwithstanding the foregoing, at any time after the grant of Restricted Stock Units, the Administrator, in its
sole discretion, may reduce or waive any vesting criteria that must be met to receive a payout. 

        (d)    Form and Timing of Payment.    Payment of earned Restricted Stock Units shall be made as soon as practicable
after the date(s) set forth in the Restricted Stock Unit Award Agreement. The Administrator may only settle earned Restricted Stock Units in Shares. 

        (e)    Cancellation.    On the date set forth in the Restricted Stock Unit Award Agreement, all unearned Restricted
Stock Units shall be forfeited to the Company. 

        9.    Stock Appreciation Rights.    

        (a)    Grant of SARs.    Subject to the terms and conditions of the Plan, a SAR may be granted to Service Providers at
any time and from time to time as will be determined by the Administrator, in its sole discretion. 

        (b)    Number of Shares.    The Administrator will have complete discretion to determine the number of SARs granted to
any Service Provider. 

        (c)    Exercise Price and Other Terms.    The per share exercise price for the Shares to be issued pursuant to
exercise of an SAR shall be determined by the Administrator and shall be no less than 100% of the Fair Market Value per share on the date of grant. Otherwise, subject to Section 6(a) of the
Plan, the Administrator, subject to the provisions of the Plan, shall have complete discretion to determine the terms and conditions of SARs granted under the Plan; provided, however, that no SAR may
have a term of more than ten (10) years from the date of grant. 

        (d)    SAR Agreement.    Each SAR grant will be evidenced by an Award Agreement that will specify the exercise price,
the term of the SAR, the conditions of exercise, and such other terms and conditions as the Administrator, in its sole discretion, will determine. 

        (e)    Expiration of SARs.    An SAR granted under the Plan will expire upon the date determined by the Administrator,
in its sole discretion, and set forth in the Award Agreement. Notwithstanding the foregoing, the rules of Section 6(d) also will apply to SARs. 

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        (f)    Payment of SAR Amount.    Upon exercise of an SAR, a Participant will be entitled to receive payment from the
Company in an amount determined by multiplying: 

          (i)  The
difference between the Fair Market Value of a Share on the date of exercise over the exercise price; times 

         (ii)  The
number of Shares with respect to which the SAR is exercised. 

        The
payment upon SAR exercise may only be in Shares of equivalent value (rounded down to the nearest whole Share). 

        10.    Performance Units and Performance Shares.    

        (a)    Grant of Performance Units/Shares.    Performance Units and Performance Shares may be granted to Service
Providers at any time and from time to time, as will be determined by the Administrator, in its sole discretion. The Administrator will have complete discretion in determining the number of
Performance Units and Performance Shares granted to each Participant. 

        (b)    Value of Performance Units/Shares.    Each Performance Unit will have an initial value that is established by
the Administrator on or before the date of grant. Each Performance Share will have an initial value equal to the Fair Market Value of a Share on the date of grant. 

        (c)    Performance Objectives and Other Terms.    The Administrator will set performance objectives or other vesting
provisions (including, without limitation, continued status as a Service Provider) in its discretion which, depending on the extent to which they are met, will determine the number or value of
Performance Units/Shares that will be paid out to the Service Providers. The time period during which the performance objectives or other vesting provisions must be met will be called the "Performance
Period." Each Award of Performance Units/Shares will be evidenced by an Award Agreement that will specify the Performance Period, and such other terms and conditions as the Administrator, in its sole
discretion, will determine. The Administrator may set performance objectives based upon the achievement of Company-wide, divisional, or individual goals, applicable federal or state
securities laws, or any other basis determined by the Administrator in its discretion. 

        (d)    Earning of Performance Units/Shares.    After the applicable Performance Period has ended, the holder of
Performance Units/Shares will be entitled to receive a payout of the number of Performance Units/Shares earned by the Participant over the Performance Period, to be determined as a function of the
extent to which the corresponding performance objectives or other vesting provisions have been achieved. After the grant of a Performance Unit/Share, the Administrator, in its sole discretion, may
reduce or waive any performance objectives or other vesting provisions for such Performance Unit/Share. 

        (e)    Form and Timing of Payment of Performance Units/Shares.    Payment of earned Performance Units/Shares will be
made as soon as practicable after the expiration of the applicable Performance Period. The Administrator, in its sole discretion, may pay earned Performance Units/Shares in the form of cash, in Shares
(which have an aggregate Fair Market Value equal to the value of the earned
Performance Units/Shares at the close of the applicable Performance Period) or in a combination thereof. 

        (f)    Cancellation of Performance Units/Shares.    On the date set forth in the Award Agreement, all unearned or
unvested Performance Units/Shares will be forfeited to the Company, and again will be available for grant under the Plan. 

        11.    Leaves of Absence.    Unless the Administrator provides otherwise, vesting of Awards granted hereunder will be
suspended during any unpaid leave of absence. A Service Provider will not cease to be an Employee in the case of (i) any leave of absence approved by the Company or (ii) transfers 

10

 

between
locations of the Company or between the Company, its Parent, or any Subsidiary. For purposes of Incentive Stock Options, no such leave may exceed ninety (90) days, unless reemployment
upon expiration of such leave is guaranteed by statute or contract. If reemployment upon expiration of a leave of absence approved by the Company is not so guaranteed, then three (3) months
following the 91st day of such leave any Incentive Stock Option held by the Participant will cease to be treated as an Incentive Stock Option and will be treated for tax purposes as a
Nonstatutory Stock Option. 

        12.    Transferability of Awards.    Unless determined otherwise by the Administrator, an Award may not be sold,
pledged, assigned, hypothecated, transferred, or disposed of in any manner other than by will or by the laws of descent or distribution and may be exercised, during the lifetime of the Participant,
only by the Participant. If the Administrator makes an Award transferable, such Award will contain such additional terms and conditions as the Administrator deems appropriate. 

        13.    Adjustments; Dissolution or Liquidation; Merger or Change in Control.    

        (a)    Adjustments.    In the event that any dividend or other distribution (whether in the form of cash, Shares,
other securities, or other property), recapitalization, stock split, reverse stock split, reorganization, merger, consolidation, split-up, spin-off, combination, repurchase, or
exchange of Shares or other securities of the Company, or other change in the corporate structure of the Company affecting the Shares occurs, the Administrator shall adjust the number and class of
Shares that may be delivered under the Plan and/or the number, class, and price of Shares covered by each outstanding Award and the numerical Share limits in Section 3 of the Plan. 

        (b)    Dissolution or Liquidation.    In the event of the proposed dissolution or liquidation of the Company, the
Administrator will notify each Participant as soon as practicable prior to the effective date of such proposed transaction. To the extent it has not been previously exercised, an Award will terminate
immediately prior to the consummation of such proposed action. 

        (c)    Change in Control.    In the event of a merger or Change in Control, each outstanding Award will be treated as
the Administrator determines, including, without limitation, that each Award be assumed or an equivalent option or right substituted by the successor corporation or a Parent or Subsidiary of the
successor corporation. The Administrator shall not be required to treat all Awards similarly in the transaction. 

        In
the event that the successor corporation does not assume or substitute for the Award, the Participant will fully vest in and have the right to exercise all of his or her outstanding
Options and SARs, including Shares as to which such Awards would not otherwise be vested or exercisable, all restrictions on Restricted Stock and Restricted Stock Units will lapse, and, with respect
to Awards with performance-based vesting, all performance goals or other vesting criteria will be deemed achieved at 100% on-target levels and all other terms and conditions met. In
addition, if an Option or SAR is not assumed or substituted in the event of a Change in Control, the Administrator will notify the Participant in writing or electronically that the Option or SAR will
be exercisable for a period of time determined by the Administrator in its sole discretion, and the Option or SAR will terminate upon the expiration of such period. 

        For
the purposes of this subsection (c), an Award will be considered assumed if, following the Change in Control, the Award confers the right to purchase or receive, for each
Share subject to the Award immediately prior to the Change in Control, the consideration (whether stock, cash, or other securities or property) received in the Change in Control by holders of Common
Stock for each Share held on the effective date of the transaction (and if holders were offered a choice of consideration, the type of consideration chosen by the holders of a majority of the
outstanding Shares); provided, however, that if such consideration received in the Change in Control is not solely common stock of the successor corporation or its Parent, the Administrator may, with
the consent of the successor corporation, provide for the consideration to be received upon the exercise of an Option or SAR or upon the payout of a Restricted Stock Unit, Performance Unit or 

11

 

Performance
Share, for each Share subject to such Award, to be solely common stock of the successor corporation or its Parent equal in fair market value to the per share consideration received by
holders of Common Stock in the Change in Control. 

        Notwithstanding
anything in this Section 13(c) to the contrary, an Award that vests, is earned or paid-out upon the satisfaction of one or more performance
goals will not be considered assumed if the Company or its successor modifies any of such performance goals without the Participant's consent; provided, however, a modification to such performance
goals only to reflect the successor corporation's post-Change in Control corporate structure will not be deemed to invalidate an otherwise valid Award assumption. 

        (d)    Outside Director Awards.    With respect to Awards granted to an Outside Director that are assumed or
substituted for, if on the date of or following such assumption or substitution the Participant's status as
a Director or a director of the successor corporation, as applicable, is terminated other than upon a voluntary resignation by the Participant (unless such resignation is at the request of the
acquirer), then the Participant will fully vest in and have the right to exercise Options and/or SARs as to all of the Shares underlying such Award, including those Shares which would not otherwise be
vested or exercisable, all restrictions on Restricted Stock and Restricted Stock Units will lapse, and, with respect to Performance Units and Performance Shares, all performance goals or other vesting
criteria will be deemed achieved at 100% on-target levels and all other terms and conditions met. 

        14.    Tax Withholding.    

        (a)    Withholding Requirements.    Prior to the delivery of any Shares or cash pursuant to an Award
(or exercise thereof), the Company will have the power and the right to deduct or withhold, or require a Participant to remit to the Company, an amount sufficient to satisfy federal, state,
local, foreign or other taxes (including the Participant's FICA obligation) required to be withheld with respect to such Award (or exercise thereof). 

        (b)    Withholding Arrangements.    The Administrator, in its sole discretion and pursuant to such procedures as it
may specify from time to time, may permit a Participant to satisfy such tax withholding obligation, in whole or in part by (a) paying cash, (b) electing to have the Company withhold
otherwise deliverable cash or Shares having a Fair Market Value equal to the minimum statutory amount required to be withheld, or (c) delivering to the Company already-owned Shares having a
Fair Market Value equal to the minimum statutory amount required to be withheld. The Fair Market Value of the Shares to be withheld or delivered will be determined as of the date that the taxes are
required to be withheld. 

        15.    No Effect on Employment or Service.    Neither the Plan nor any Award will confer upon a Participant any right
with respect to continuing the Participant's relationship as a Service Provider with the Company, nor will they interfere in any way with the Participant's right or the Company's right to terminate
such relationship at any time, with or without cause, to the extent permitted by Applicable Laws. 

        16.    Date of Grant.    The date of grant of an Award will be, for all purposes, the date on which the Administrator
makes the determination granting such Award, or such other later date as is determined by the Administrator. Notice of the determination will be provided to each Participant within a reasonable time
after the date of such grant. 

        17.    Term of Plan.    Subject to Section 21 of the Plan, the Plan will become effective upon its adoption by
the Board. It will continue in effect for a term of ten (10) years from the date adopted by the Board unless terminated earlier under Section 18 of the Plan. 

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        18.    Amendment and Termination of the Plan.    

        (a)    Amendment and Termination.    The Board may at any time amend, alter, suspend or terminate the Plan. 

        (b)    Stockholder Approval.    The Company will obtain stockholder approval of any Plan amendment to the extent
necessary and desirable to comply with Applicable Laws. 

        (c)    Effect of Amendment or Termination.    No amendment, alteration, suspension or termination of the Plan will
impair the rights of any Participant, unless mutually agreed otherwise between the Participant and the Administrator, which agreement must be in writing and signed by the Participant and the Company.
Termination of the Plan will not affect the Administrator's ability to exercise the powers granted to it hereunder with respect to Awards granted under the Plan prior to the date of such termination. 

        19.    Conditions Upon Issuance of Shares.    

        (a)    Legal Compliance.    Shares will not be issued pursuant to the exercise of an Award unless the exercise of such
Award and the issuance and delivery of such Shares will comply with Applicable Laws and will be further subject to the approval of counsel for the Company with respect to such compliance. 

        (b)    Investment Representations.    As a condition to the exercise of an Award, the Company may require the person
exercising such Award to represent and warrant at the time of any such exercise that the Shares are being purchased only for investment and without any present intention to sell or distribute such
Shares if, in the opinion of counsel for the Company, such a representation is required. 

        20.    Inability to Obtain Authority.    The inability of the Company to obtain authority from any regulatory body
having jurisdiction, which authority is deemed by the Company's counsel to be necessary to the lawful issuance and sale of any Shares hereunder, will relieve the Company of any liability in respect of
the failure to issue or sell such Shares as to which such requisite authority will not have been obtained. 

        21.    Stockholder Approval.    The Plan will be subject to approval by the stockholders of the Company within twelve
(12) months after the date the Plan is adopted by the Board. Such stockholder approval will be obtained in the manner and to the degree required under Applicable Laws. 

13

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Exhibit 10.23

OPTIMER PHARMACEUTICALS, INC. 2006 EQUITY INCENTIVE PLANQuickLinks
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Exhibit 10.24    
    

 
 

OPTIMER PHARMACEUTICALS, INC.
  EMPLOYEE STOCK PURCHASE PLAN    
    

        1.    Purpose.    The purpose of the Plan is to provide employees of the Company and its Designated Subsidiaries with
an opportunity to purchase Common Stock of the Company through accumulated payroll deductions. It is the intention of the Company to have the Plan qualify as an "Employee Stock Purchase Plan" under
Section 423 of the Code. The provisions of the Plan, accordingly, shall be construed so as to extend and limit participation in a uniform and nondiscriminatory basis consistent with the
requirements of Section 423. 

        2.    Definitions.    

        (a)   "Administrator" shall mean the Board or any Committee designated by the Board to administer the plan pursuant to
Section 14. 

        (b)   "Board" shall mean the Board of Directors of the Company. 

        (c)   "Change in Control" means the occurrence of any of the following events: 

          (i)  Any
"person" (as such term is used in Sections 13(d) and 14(d) of the Exchange Act) becomes the "beneficial owner" (as defined in
Rule 13d-3 of the Exchange Act), directly or indirectly, of securities of the Company representing fifty percent (50%) or more of the total voting power represented by the Company's
then outstanding voting securities; or 

         (ii)  The
consummation of the sale or disposition by the Company of all or substantially all of the Company's assets; or 

        (iii)  A
change in the composition of the Board occurring within a two-year period, as a result of which fewer than a majority of the directors are Incumbent
Directors. "Incumbent Directors" means directors who either (A) are Directors as of the effective date of the Plan, or (B) are elected, or nominated for election, to the Board with the
affirmative votes of at least a majority of the Directors at the time of such election or nomination (but will not include an individual whose election or nomination is in connection with an
actual or threatened proxy contest relating to the election of directors to the Company); or 

        (iv)  The
consummation of a merger or consolidation of the Company with any other corporation, other than a merger or consolidation which would result in the voting
securities of the Company outstanding immediately prior thereto continuing to represent (either by remaining outstanding or by being converted into voting securities of the surviving entity or its
parent) at least fifty percent (50%) of the total voting power represented by the voting securities of the Company or such surviving entity or its parent outstanding immediately after such merger or
consolidation. 

        (d)   "Code" shall mean the Internal Revenue Code of 1986, as amended. 

        (e)   "Committee" means a committee of the Board appointed in accordance with Section 14 hereof. 

        (f)    "Common Stock" shall mean the common stock of the Company. 

        (g)   "Company" shall mean Optimer Pharmaceuticals, Inc., a Delaware corporation. 

        (h)   "Compensation" shall mean all base straight time gross earnings, commissions, overtime and shift premium, but exclusive
of payments for incentive compensation, bonuses and other compensation. 

        (i)    "Designated Subsidiary" shall mean any Subsidiary selected by the Administrator as eligible to participate in
the Plan. 

 

        (j)    "Director" shall mean a member of the Board. 

        (k)   "Eligible Employee" shall mean any individual who is a common law employee of the Company or any Designated Subsidiary
and whose customary employment with the Company or Designated Subsidiary is at least twenty (20) hours per week and more than five (5) months in any calendar year. For purposes of the
Plan, the employment relationship shall be treated as continuing intact while the individual is on sick leave or other leave of absence approved by the Company. Where the period of leave exceeds
90 days and the individual's right to reemployment is not guaranteed either by statute or by contract, the employment relationship shall be deemed to have terminated on the 91st day of
such leave. 

        (l)    "Exchange Act" shall mean the Securities Exchange Act of 1934, as amended. 

        (m)  "Exercise Date" shall mean the first Trading Day on or after May 15 and November 15 of each year. The first
Exercise Date under the Plan shall be November 15, 2007. 

        (n)   "Fair Market Value" shall mean, as of any date and unless the Administrator determines otherwise, the value of Common
Stock determined as follows: 

          (i)  If
the Common Stock is listed on any established stock exchange or a national market system, including without limitation the Nasdaq Global Market, its Fair Market
Value shall be the closing sales price for such stock (or the closing bid, if no sales were reported) as quoted on such exchange or system on the date of determination, as reported in  The Wall Street
Journal or such other source as the Board deems reliable; 

         (ii)  If
the Common Stock is regularly quoted by a recognized securities dealer but selling prices are not reported, its Fair Market Value shall be the mean of the closing
bid and asked prices for the Common Stock on the date of determination, as reported in The Wall Street Journal or such other source as the Board
deems reliable; 

        (iii)  In
the absence of an established market for the Common Stock, the Fair Market Value thereof shall be determined in good faith by the Board; or 

        (iv)  For
purposes of the Offering Date of the first Offering Period under the Plan, the Fair Market Value shall be the initial price to the public as set forth in the final
prospectus included within the registration statement on Form S-1 filed with the Securities and Exchange Commission for the initial public offering of the Company's Common Stock
(the "Registration Statement"). 

        (o)   "Fiscal Year" means the fiscal year of the Company. 

        (p)   "Offering Date" shall mean the first Trading Day of each Offering Period. 

        (q)   "Offering Periods" shall mean the periods of approximately six (6) months during which an option granted pursuant
to the Plan may be exercised, commencing on the first Trading Day on or after May 15 and November 15 of each year and terminating on the first Trading Day on or after the subsequent
Offering Period commencement date approximately six months later; provided, however, that the first Offering Period under the Plan shall commence with the first Trading Day on or after the date on
which the Securities and Exchange Commission declares the Company's registration statement on Form S-1 effective and end on the first Trading Day on or after November 15,
2007 and the second Offering Period under the Plan shall commence with the first Trading Day on or after November 16, 2007. The duration and timing of Offering Periods may be changed pursuant
to Section 4 of this Plan. 

        (r)   "Plan" shall mean this Optimer Pharmaceuticals, Inc. Employee Stock Purchase Plan. 

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        (s)   "Purchase Price" shall mean an amount equal to eighty-five percent (85%) of the Fair Market Value of a share
of Common Stock on the Offering Date or on the Exercise Date, whichever is lower; provided however, that the Purchase Price may be determined for subsequent Offering Periods by the Administrator
subject to compliance with Section 423 of the Code (or any successor rule or provision or any other applicable law, regulation or stock exchange rule) or pursuant to Section 20. 

        (t)    "Subsidiary" shall mean a "subsidiary corporation," whether now or hereafter existing, as defined in
Section 424(f) of the Code. 

        (u)   "Trading Day" shall mean a day on which the national stock exchange upon which the Company Common Stock is listed is open
for trading. 

        3.    Eligibility.    

        (a)   First Offering Period.    Any individual who is an Eligible Employee immediately prior to the first Offering
Period shall be automatically enrolled in the first Offering Period. 

        (b)   Subsequent Offering Periods.    Any Eligible Employee on a given Offering Date shall be eligible to participate
in the Plan. 

        (c)   Limitations.    Any provisions of the Plan to the contrary notwithstanding, no Eligible Employee shall be
granted an option under the Plan (i) to the extent that, immediately after the grant, such Eligible Employee (or any other person whose stock would be attributed to such Eligible
Employee pursuant to Section 424(d) of the Code) would own capital stock of the Company and/or hold outstanding options to purchase such stock possessing five percent (5%) or more of the total
combined voting power or value of all classes of the capital stock of the Company or of any Subsidiary, or (ii) to the extent that his or her rights to purchase stock under all employee stock
purchase plans of the Company and its subsidiaries accrues at a rate which exceeds Twenty-Five Thousand Dollars ($25,000) worth of stock (determined at the fair market value of the shares
at the time such option is granted) for each calendar year in which such option is outstanding at any time. 

        4.    Offering Periods.    The Plan shall be implemented by consecutive Offering Periods with a new Offering Period
commencing on the first Trading Day on or after May 15 and November 15 each year, or on such other date as the Board shall determine; provided, however, that the first Offering Period
under the Plan shall commence with the first Trading Day on or after the date upon which the Company's Registration Statement is declared effective by the Securities and Exchange Commission and end on
the first Trading Day on or after November 15, 2007. The Board shall have the power to change the duration of Offering Periods (including the commencement dates thereof) with respect to future
offerings without stockholder approval if such change is announced prior to the scheduled beginning of the first Offering Period to be affected thereafter. 

        5.    Participation.    

        (a)   First Offering Period.    An Eligible Employee shall be entitled to participate in the first Offering Period
only if such individual submits a subscription agreement authorizing payroll deductions in a form determined by the Administrator (which may be similar to the form attached hereto as Exhibit A)
to the Company's designated plan administrator (i) no earlier than the effective date of the Form S-8 registration statement with respect to the issuance of Common
Stock under this Plan and (ii) no later than twenty (20) business days following the effective date of such S-8 registration statement (the "Enrollment
Window"). An Eligible Employee's failure to submit the subscription agreement during the Enrollment Window shall result in the automatic termination of such individual's participation in the Offering
Period. 

3

 

        (b)   Subsequent Offering Periods.    An Eligible Employee may become a participant in the Plan by completing a
subscription agreement in a form determined by the Administrator (which may be similar to the form attached hereto as Exhibit A) and filing it with the Company's designated Plan
administrator prior to the applicable Offering Date. 

        6.    Payroll Deductions.    

        (a)   At
the time a participant files his or her subscription agreement, he or she shall elect to have payroll deductions made on each pay day during the Offering Period in an
amount not exceeding 10% of the Compensation which he or she receives on each pay day during the Offering Period; provided, however, that should a pay day occur on an Exercise Date, a participant
shall have the payroll deductions made on such day applied to his or her account under the new Offering Period. A participant's subscription agreement shall remain in effect for successive Offering
Periods unless terminated as provided in Section 10 hereof. 

        (b)   Payroll
deductions for a participant shall commence on the first pay day following the Offering Date and shall end on the last pay day in the Offering Period to which
such authorization is applicable, unless sooner terminated by the participant as provided in Section 10 hereof; provided, however, that for the first Offering Period, payroll deductions shall
commence on the first pay day on or following the end of the Enrollment Window. 

        (c)   All
payroll deductions made for a participant shall be credited to his or her account under the Plan and shall be withheld in whole percentages only. A participant may
not make any additional payments into such account. 

        (d)   A
participant may discontinue his or her participation in the Plan as provided in Section 10 hereof, or may increase or decrease the rate of his or her
payroll deductions during the Offering Period by completing or filing with the Company a new subscription agreement authorizing a change in payroll
deduction rate. The Administrator may, in its discretion, limit the nature and/or number of participation rate changes during any Offering Period. The change in rate shall be effective with the first
full payroll period following five (5) business days after the Company's receipt of the new subscription agreement unless the Company elects to process a given change in participation
more quickly. 

        (e)   Notwithstanding
the foregoing, to the extent necessary to comply with Section 423(b)(8) of the Code and Section 3(c) hereof, a participant's payroll
deductions may be decreased to zero percent (0%) at any time during an Offering Period. Payroll deductions shall recommence at the rate provided in such participant's subscription agreement at the
beginning of the first Offering Period which is scheduled to end in the following calendar year, unless terminated by the participant as provided in Section 10 hereof. 

        (f)    At
the time the option is exercised, in whole or in part, or at the time some or all of the Company's Common Stock issued under the Plan is disposed of, the participant
must make adequate provision for the Company's or its Subsidiary's federal, state, or any other tax liability payable to any authority, national insurance, social security or other tax withholding
obligations, if any, which arise upon the exercise of the option or the disposition of the Common Stock. At any time, the Company or its Subsidiary may, but shall not be obligated to, withhold from
the participant's compensation the amount necessary for the Company or its Subsidiary to meet applicable withholding obligations, including any withholding required to make available to the Company or
its Subsidiary any tax deductions or benefits attributable to sale or early disposition of Common Stock by the Eligible Employee. 

        7.    Grant of Option.    On the Offering Date of each Offering Period, each Eligible Employee participating in such
Offering Period shall be granted an option to purchase on each Exercise Date during such Offering Period (at the applicable Purchase Price) up to a number of shares of the 

4

 

Company's
Common Stock determined by dividing such Eligible Employee's payroll deductions accumulated prior to such Exercise Date by the applicable Purchase Price; provided that in no event shall an
Eligible Employee be permitted to purchase during each Offering Period more than            shares of the Company's Common Stock (subject to any adjustment pursuant to Section 19), and
provided further that such purchase shall be subject to the limitations set forth in Sections 3(c) and 13 hereof. The Eligible Employee may accept the grant of such option by turning in
a completed Subscription Agreement (attached hereto as Exhibit A) to the Company on or prior to an Offering Date, or with respect to the
first Offering Period, prior to the last day of the Enrollment Window. The Administrator may, for future Offering Periods, increase or decrease, in its absolute discretion, the maximum number of
shares of the Company's Common Stock an Eligible Employee may purchase during each Offering Period. Exercise of the option shall occur as provided in Section 8 hereof, unless the participant
has withdrawn pursuant to Section 10 hereof. The option shall expire on the last day of the Offering Period. 

        8.    Exercise of Option.    

        (a)   Unless
a participant withdraws from the Plan as provided in Section 10 hereof, his or her option for the purchase of shares shall be exercised automatically on
the Exercise Date, and the maximum number of full shares subject to option shall be purchased for such participant at the applicable Purchase Price with the accumulated payroll deductions in his or
her account. No fractional shares shall be purchased; any payroll deductions accumulated in a participant's account which are not sufficient to purchase a full share shall be retained in the
participant's account for the subsequent Offering Period, subject to earlier withdrawal by the participant as provided in Section 10 hereof. Any other funds left over in a participant's account
after the Exercise Date shall be returned to the participant. During a participant's lifetime, a participant's option to purchase shares hereunder is exercisable only by him or her. 

        (b)   If
the Administrator determines that, on a given Exercise Date, the number of shares with respect to which options are to be exercised may exceed (i) the number
of shares of Common Stock that were available for sale under the Plan on the Offering Date of the applicable Offering Period, or (ii) the number of shares available for sale under the Plan on
such Exercise Date, the Administrator may in its sole discretion provide that the Company shall make a pro rata allocation of the shares of Common Stock available for purchase on such Exercise
Date in as uniform a manner as shall be practicable and as it shall determine in its sole discretion to be equitable among all participants exercising options to purchase Common Stock on such Exercise
Date. The Company may make a pro rata allocation of the shares available on the Offering Date of any applicable Offering Period pursuant to the preceding sentence, notwithstanding any
authorization of additional shares for issuance under the Plan by the Company's stockholders subsequent to such Offering Date. 

        9.    Delivery.    As soon as reasonably practicable after each Exercise Date on which a purchase of shares occurs,
the Company shall arrange the delivery to each participant the shares purchased upon exercise of his or her option in a form determined by the Administrator. 

        10.    Withdrawal.    

        (a)   A
participant may withdraw all but not less than all the payroll deductions credited to his or her account and not yet used to exercise his or her option under the Plan
at any time by giving written notice to the Company in the form determined by the Administrator (which may be similar to the form attached as  Exhibit B to this Plan). All of the participant's
payroll deductions credited to his or her account shall be paid to such participant
promptly after receipt of notice of withdrawal and such participant's option for the Offering Period shall be automatically terminated, and no further payroll deductions for the purchase of shares
shall be made for such Offering Period. If a participant withdraws from an Offering Period, payroll deductions shall not resume at 

5

 

the
beginning of the succeeding Offering Period unless the participant delivers to the Company a new subscription agreement. 

        (b)   A
participant's withdrawal from an Offering Period shall not have any effect upon his or her eligibility to participate in any similar plan which may hereafter be
adopted by the Company or in succeeding Offering Periods which commence after the termination of the Offering Period from which the participant withdraws. 

        11.    Termination of Employment.    Upon a participant's ceasing to be an Eligible Employee, for any reason, he or
she shall be deemed to have elected to withdraw from the Plan and the payroll deductions credited to such participant's account during the Offering Period but not yet used to purchase shares of Common
Stock under the Plan shall be returned to such participant or, in the case of his or her death, to the person or persons entitled thereto under Section 15, and such participant's option shall
be automatically terminated. 

        12.    Interest.    No interest shall accrue on the payroll deductions of a participant in the Plan. 

        13.    Stock.    

        (a)   Subject
to adjustment upon changes in capitalization of the Company as provided in Section 19 hereof, the maximum number of shares of the Company's Common Stock
which shall be made available for sale under the Plan shall be             shares (which has been determined after adjustment to reflect the stock split which will be completed by the
Company prior to the initial registration of the Company's Common Stock under Section 12 of the Exchange Act) plus an annual increase to be added on the first day of each Company Fiscal Year
beginning with the 2008 Fiscal Year, equal to the lesser of (i)             shares of Common Stock (which has been determined after adjustment to reflect the stock split which will be
completed by the Company prior to the initial registration of the Company's Common Stock under Section 12 of the Exchange Act), (ii) three percent (3%) of the outstanding shares of
Common Stock on the last day of the immediately preceding Fiscal Year or (iii) an amount determined by the Board. 

        (b)   Until
the shares are issued (as evidenced by the appropriate entry on the books of the Company or of a duly authorized transfer agent of the Company), a
participant shall only have the rights of an unsecured creditor with respect to such shares, and no right to vote or receive dividends or any other rights as a stockholder shall exist with respect to
such shares. 

        (c)   Shares
to be delivered to a participant under the Plan shall be registered in the name of the participant or in the name of the participant and his or her spouse. 

        14.    Administration.    The Plan will be administered by an Administrator which shall be either (A) the Board
or (B) a Committee appointed by the Board, which committee will be constituted to satisfy all applicable law. The Administrator shall administer the Plan and shall have full and exclusive
discretionary authority to construe, interpret and apply the terms of the Plan, to determine eligibility and to adjudicate all disputed claims filed under the Plan. Every finding, decision and
determination made by the Administrator shall, to the full extent permitted by law, be final and binding upon all parties. Notwithstanding any provision to the contrary in this Plan, the Administrator
may adopt rules or procedures relating to the operation and administration of the Plan to accommodate the specific requirements of local laws and procedures for jurisdictions outside of the
United States. Without limiting the generality of the foregoing, the Administrator is specifically authorized to adopt rules and procedures regarding eligibility to participate, the definition
of Compensation, handling of payroll deductions, making of contributions to the Plan (including, without limitation, in forms other than payroll deductions), establishment of bank or trust accounts to
hold payroll deductions, payment of interest, conversion of local currency, obligations to pay payroll tax, determination of beneficiary designation requirements, withholding procedures and handling
of stock certificates which vary with local requirements. 

6

 

        15.    Designation of Beneficiary.    

        (a)   A
participant may file a designation of a beneficiary who is to receive any shares and cash, if any, from the participant's account under the Plan in the event of
such participant's death subsequent to an Exercise Date on which the option is exercised but prior to delivery to such participant of such shares and cash. In addition, a participant may file a
designation of a beneficiary who is to receive any cash from the participant's account under the Plan in the event of such participant's death prior to exercise of the option. If a participant is
married and the designated beneficiary is not the spouse, spousal consent shall be required for such designation to be effective. 

        (b)   Such
designation of beneficiary may be changed by the participant at any time by notice in a form determined by the Administrator. In the event of the death of a
participant and in the absence of a beneficiary validly designated under the Plan who is living at the time of such participant's death, the Company shall deliver such shares and/or cash to the
executor or administrator of the estate of the participant, or if no such executor or administrator has been appointed (to the knowledge of the Company), the Company, in its discretion, may
deliver such shares and/or cash to the spouse or to any one or more dependents or relatives of the participant, or if no spouse, dependent or relative is known to the Company, then to such other
person as the Company may designate. 

        (c)   All
beneficiary designations shall be in such form and manner as the Administrator may designate from time to time. 

        16.    Transferability.    Neither payroll deductions credited to a participant's account nor any rights with regard
to the exercise of an option or to receive shares under the Plan may be assigned, transferred, pledged or otherwise disposed of in any way (other than by will, the laws of descent and distribution or
as provided in Section 15 hereof) by the participant. Any such attempt at assignment, transfer, pledge or other disposition shall be without effect, except that the Company may treat such act
as an election to withdraw funds from an Offering Period in accordance with Section 10 hereof. 

        17.    Use of Funds.    All payroll deductions received or held by the Company under the Plan may be used by the
Company for any corporate purpose, and the Company shall not be obligated to segregate such payroll deductions. Until shares are issued, participants shall only have the rights of an unsecured
creditor. 

        18.    Reports.    Individual accounts shall be maintained for each participant in the Plan. Statements of account
shall be given to participating Eligible Employees at least annually, which statements shall set forth the amounts of payroll deductions, the Purchase Price, the number of shares purchased and the
remaining cash balance, if any. 

        19.    Adjustments Upon Changes in Capitalization, Dissolution, Liquidation, Merger or Change in Control.    

        (a)   Changes in Capitalization.    Subject to any required action by the stockholders of the Company, the maximum
number of shares of the Company's Common Stock which shall be made available for sale under the Plan, the maximum number of shares each participant may purchase each Offering Period (pursuant to
Section 7), as well as the price per share and the number of shares of Common Stock covered by each option under the Plan which has not yet been exercised shall be proportionately adjusted for
any increase or decrease in the number of issued shares of Common Stock resulting from a stock split, reverse stock split, stock dividend, combination or reclassification of the Common Stock, or any
other change in the number of shares of Common Stock effected without receipt of consideration by the Company; provided, however, that conversion of any convertible securities of the Company shall not
be deemed to have been "effected without receipt of consideration." Such adjustment shall be made by the Administrator, 

7

 

whose
determination in that respect shall be final, binding and conclusive. Except as expressly provided herein, no issuance by the Company of shares of stock of any class, or securities convertible
into shares of stock of any class, shall affect, and no adjustment by reason thereof shall be made with respect to, the number or price of shares of Common Stock subject to an option. 

        (b)   Dissolution or Liquidation.    In the event of the proposed dissolution or liquidation of the Company, the
Offering Period then in progress shall be shortened by setting a new Exercise Date (the "New Exercise Date"), and shall terminate immediately prior to the consummation of such proposed
dissolution or liquidation, unless provided otherwise by the Administrator. The New Exercise
Date shall be before the date of the Company's proposed dissolution or liquidation. The Administrator shall notify each participant in writing, at least ten (10) business days prior to the
New Exercise Date, that the Exercise Date for the participant's option has been changed to the New Exercise Date and that the participant's option shall be exercised automatically on the
New Exercise Date, unless prior to such date the participant has withdrawn from the Offering Period as provided in Section 10 hereof. 

        (c)   Merger or Change in Control.    In the event of a merger or Change in Control, each outstanding option
shall be assumed or an equivalent option substituted by the successor corporation or a Parent or Subsidiary of the successor corporation. In the event that the successor corporation refuses to assume
or substitute for the option, the Offering Period then in progress shall be shortened by setting a New Exercise Date and shall end on the New Exercise Date. The New Exercise Date
shall be before the date of the Company's proposed merger or Change in Control. The Administrator shall notify each participant in writing, at least ten (10) business days prior to the
New Exercise Date, that the Exercise Date for the participant's option has been changed to the New Exercise Date and that the participant's option shall be exercised automatically on the
New Exercise Date, unless prior to such date the participant has withdrawn from the Offering Period as provided in Section 10 hereof. 

        20.    Amendment or Termination.    

        (a)   The
Administrator may at any time and for any reason terminate or amend the Plan. Except as provided in Section 19 and this Section 20 hereof, no
amendment may make any change in any option theretofore granted which adversely affects the rights of any participant unless their consent is obtained. To the extent necessary to comply with
Section 423 of the Code (or any successor rule or provision or any other applicable law, regulation or stock exchange rule), the Company shall obtain stockholder approval of any
amendment in such a manner and to such a degree as required. 

        (b)   Without
stockholder approval and without regard to whether any participant rights may be considered to have been "adversely affected," the Administrator shall be
entitled to change the Offering Periods, limit the frequency and/or number of changes in the amount withheld during an Offering Period, establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars, permit payroll withholding in excess of the amount designated by a participant in order to adjust for delays or mistakes in the Company's processing of
properly completed withholding elections, establish reasonable waiting and adjustment periods and/or accounting and crediting procedures to ensure that amounts applied toward the purchase of Common
Stock for each participant properly correspond with amounts withheld from the participant's Compensation, and establish such other limitations or procedures as the Administrator determines in its sole
discretion advisable which are consistent with the Plan. 

        (c)   Without
regard to whether any participant's rights may be considered to have been "adversely affected", in the event the Administrator determines that the ongoing
operation of the Plan may result in unfavorable financial accounting consequences, the Board may, in its discretion 

8

 

and,
to the extent necessary or desirable, modify or amend the Plan to reduce or eliminate such accounting consequence including: 

          (i)  increasing
the Purchase Price for any Offering Period including an Offering Period underway at the time of the change in Purchase Price; 

         (ii)  shortening
any Offering Period so that Offering Period ends on a new Exercise Date, including an Offering Period underway at the time of the Board action; and 

        (iii)  reducing
the number of shares that may be purchased upon exercise of outstanding options. 

        Such
modifications or amendments shall not require stockholder approval or the consent of any Plan participants. 

        21.    Notices.    All notices or other communications by a participant to the Company under or in connection with the
Plan shall be deemed to have been duly given when received in the form and manner specified by the Company at the location, or by the person, designated by the Company for the receipt thereof. 

        22.    Conditions Upon Issuance of Shares.    Shares shall not be issued with respect to an option unless the exercise
of such option and the issuance and delivery of such shares pursuant thereto shall comply with all applicable provisions of law, domestic or foreign, including, without limitation, the Securities Act
of 1933, as amended, the Exchange Act, the rules and regulations promulgated thereunder, and the requirements of any stock exchange upon which the shares may then be listed, and shall be further
subject to the approval of counsel for the Company with respect to such compliance. 

        As
a condition to the exercise of an option, the Company may require the person exercising such option to represent and warrant at the time of any such exercise that the shares are being
purchased only for investment and without any present intention to sell or distribute such shares if, in the opinion of counsel for the Company, such a representation is required by any of the
aforementioned applicable provisions of law. 

        23.    Term of Plan.    The Plan shall become effective upon the earlier to occur of its adoption by the Board of
Directors or its approval by the stockholders of the Company. It shall continue in effect until the later of (i) the date it is terminated under Section 20 hereof or (ii) the date
which is ten (10) years after the date such Plan is approved by the Board. 

        24.    Stockholder Approval.    The Plan will be subject to approval by the stockholders of the Company within twelve
(12) months after the date the Plan is adopted by the Board. Such stockholder approval will be obtained in the manner and to the degree required under Applicable Laws. 

9

 
 

EXHIBIT A
  
    OPTIMER PHARMACEUTICALS, INC.
  EMPLOYEE STOCK PURCHASE PLAN
  SUBSCRIPTION AGREEMENT    
    

	                        	Original Application	 	Offering Date:	                                        
        
	
                         	

Change in Payroll Deduction Rate	
 	

 	

 
	
                         	

Change of Beneficiary(ies)	
 	

 	

 

	1.
	                                    hereby
elects to participate in the Optimer Pharmaceuticals, Inc. Employee Stock Purchase Plan (the "Employee Stock Purchase Plan") and subscribes to
purchase shares of Optimer Pharmaceuticals, Inc.'s (the "Company") Common Stock in accordance with this Subscription Agreement and the Employee Stock Purchase Plan.

	2.
	I
hereby authorize payroll deductions from each paycheck in the amount of                        % of my Compensation on each pay
day (from 0 to 10%) during the Offering Period in accordance
with the Employee Stock Purchase Plan. (Please note that no fractional percentages are permitted.)

	3.
	I
understand that said payroll deductions shall be accumulated for the purchase of shares of Common Stock at the applicable Purchase Price determined in accordance with the Employee
Stock Purchase Plan. I understand that if I do not withdraw from an Offering Period, any accumulated payroll deductions will be used to automatically exercise my option and purchase Common Stock under
the Employee Stock Purchase Plan.

	4.
	I
have received a copy of the complete Employee Stock Purchase Plan and its accompanying prospectus. I understand that my participation in the Employee Stock Purchase Plan is in all
respects subject to the terms of the Plan.

	5.
	Shares
purchased for me under the Employee Stock Purchase Plan should be issued in the name(s) of (Eligible Employee or Eligible Employee and Spouse only).

	6.
	I
understand that if I dispose of any shares received by me pursuant to the Employee Stock Purchase Plan within 2 years after the Offering Date (the first day of the
Offering Period during which I purchased such shares) or one year after the Exercise Date, I will be treated for federal income tax purposes as having received ordinary income at the time of such
disposition in an amount equal to the excess of the fair market value of the shares at the time such shares were purchased by me over the price which I paid for the shares. I
hereby agree to notify the Company in writing within 30 days after the date of any disposition of my shares and I will make adequate provision for Federal, state or other tax withholding
obligations, if any, which arise upon the disposition of the Common Stock. The Company may, but will not be obligated to, withhold from my compensation the amount necessary to
meet any applicable withholding obligation including any withholding necessary to make available to the Company any tax deductions or benefits attributable to sale or early disposition of Common Stock
by me. If I dispose of such shares at any time after the expiration of the 2-year and 1-year holding periods, I understand that I will be treated for federal income tax
purposes as having received income only at the time of such disposition, and that such income will be taxed as ordinary income only to the extent of an amount equal to the lesser of (1) the
excess of the fair market value of the shares at the time of such disposition over the purchase price which I paid for the shares, or (2) 15% of the fair market value of the shares on the first
day of the Offering Period. The remainder of the gain, if any, recognized on such disposition will be taxed as capital gain.

	7.
	I
hereby agree to be bound by the terms of the Employee Stock Purchase Plan. The effectiveness of this Subscription Agreement is dependent upon my eligibility to participate in the
Employee Stock Purchase Plan. 

	8.
	In
the event of my death, I hereby designate the following as my beneficiary(ies) to receive all payments and shares due me under the Employee Stock Purchase Plan: 

	
 	

NAME: (Please print)	

 
	 	 	
 (First)
                                (Middle)
                                (Last)

	
 	

 Relationship	
 	

	
 	

 Percentage of Benefit	
 	

 (Address)

	
 	

NAME: (Please print)	

 
	 	 	
 (First)
                                (Middle)
                                (Last)

	
 	

 Relationship	
 	

	
 	

 Percentage of Benefit	
 	

 (Address)

	
 	

Employee's Social Security Number:	

 
	 	 	

	
 	

Employee's Address:	

 
	
 	

 	

	
 	

 	

	
 	

 	

I UNDERSTAND THAT THIS SUBSCRIPTION AGREEMENT SHALL REMAIN IN EFFECT THROUGHOUT SUCCESSIVE OFFERING PERIODS UNLESS TERMINATED BY ME. 

	
 Dated:	
 	

 	
 	

 
	 	 	
	 	
 Signature of Employee
	
 	
 	

 	
 	

 Spouse's Signature (If beneficiary other than spouse)

 
 

EXHIBIT B
  
    OPTIMER PHARMACEUTICALS, INC.
  EMPLOYEE STOCK PURCHASE PLAN
  NOTICE OF WITHDRAWAL    
    

        The undersigned participant in the Offering Period of the Optimer Pharmaceuticals, Inc. Employee Stock Purchase Plan that began
on                                    ,
                        (the "Offering Date") hereby notifies the Company that he or she hereby withdraws from the Offering
Period. He or she hereby directs the Company to pay to the undersigned as
promptly as practicable all the payroll deductions credited to his or her account with respect to such Offering Period. The undersigned understands and agrees that his or her option for such Offering
Period will be automatically terminated. The undersigned understands further that no further payroll deductions will be made for the purchase of shares in the current Offering Period and the
undersigned shall be eligible to participate in succeeding Offering Periods only by delivering to the Company a new Subscription Agreement. 

	
 	
 	

Name and Address of Participant:
	
 	
 	

	 	 	

	 	 	

	 	 	Signature:
	
 	
 	

	 	 	Date:
	
 	
 	

QuickLinks

Exhibit 10.24

OPTIMER PHARMACEUTICALS, INC. EMPLOYEE STOCK PURCHASE PLAN

EXHIBIT A OPTIMER PHARMACEUTICALS, INC. EMPLOYEE STOCK PURCHASE PLAN SUBSCRIPTION AGREEMENT

EXHIBIT B OPTIMER PHARMACEUTICALS, INC. EMPLOYEE STOCK PURCHASE PLAN NOTICE OF WITHDRAWAL

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