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                                                                  Exhibit 10.11

[LETTERHEAD FOR AMBRYX INC.]


February 21, 2000

Dr. Mark J. Zoller
7 Sutton Place
Weston, MA 02193

Telephone: 781-894-6190


Dear Mark:

It is my pleasure to provide you with this letter, a formal offer, setting
forth the principal terms for you to join Ambryx Inc., a Delaware
corporation (the "Company"), which is located in La Jolla, California.

POSITION:     Vice President, Research. You will report to Dr. Lubert Stryer,
              Chairman of the Board of Directors and Chief Scientific Officer.

COMPENSATION: Monthly compensation will be $18,333.34 per month.

EQUITY:       You will be entitled to purchase at fair market value 200,000
              thousand shares of the common stock of the Company. The price
              per share of such stock will be set by the Board of Ambryx and
              your shares must be purchased within ten (10) days of your
              Start Date and will be subject to the Company's Stock Purchase
              Agreement. Your shares will vest according to the following
              schedule: (i) twenty five percent (25%) of the total (50,000
              shares) will vest upon the first anniversary of the commencement
              of your employment with the Company; (ii) one forty-eighth (1/48)
              of the total (approximately 4,166 shares) will vest each month
              beginning at the end of the one year and will continue to vest
              over a three year period.

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Dr. Mark Zoller
Page 2


BENEFITS:     You will be entitlted to receive standard medical, life and
              dental insurance benefits similar to those typically afforded in
              similar-sized biotechnology companies.

SIGN-ON
INCENTIVE:    You will be entitled to a one-time, sign-on incentive bonus.
              The bonus will be one of the following two options that you
              must elect in writing when you accept this offer: 1) a one-time
              bonus of $275,000 (two hundred seventy five thousand dollars)
              to be paid on your first day of employment that will be
              forgiven on the first day of your 37th month of employment. If
              you leave the company for any reason prior to the 37th month of
              employment, the full bonus must be repaid to Ambryx OR 2) a
              $210,000 (two hundred ten thousand dollars) one-time bonus to
              be paid on your first day of employment which will be forgiven
              annually at the rate of $70,000 (seventy thousand dollars) per
              year (on the first day of your 13th, 25th and 37th months of
              employment). If you leave at any time prior to the first day of
              your 13th month of employment, the full amount must be repaid
              to Ambryx. If you leave at any time prior to the first day of
              your 25th month of employment, $140,000 (one hundred forty
              thousand dollars) must be repaid to Ambryx. If you leave at any
              time prior to the first day of your 37th month of employment
              $70,000 (seventy thousand dollars) must be repaid to Ambryx. In
              the event that you are permanently disabled or die prior to
              repayment of any or all of the bonus, the unvested portion of
              the bonus will become due within eighteen (18) months of such
              permanent disability or death.

MOVE AND
RELOCATION:   You will be entitled to reasonable move and relocation
              reimbursement including transportation of your personal
              possessions and automobiles, travel to San Diego for you and
              your family, closing costs (including legal fees, points and
              commissions, not to exceed $20,000 for closing costs), three
              months temporary housing and other miscellaneous expenses as
              discussed and agreed in advance. Expenses paid by you will be
              adjusted to reflect your pre-tax cost.

VACATION:     You will be entitled to 17 days per year of paid personal leave.

EMPLOYMENT
AT WILL:      Your employment will be at will, which means it may be
              terminated at any time by you or the Company with or without
              cause.

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START DATE:   March 10, 2000, or at another mutually agreeable date. This offer
              is subject to proof of United States Citizenship or other proof
              of employability in the United States and if not accepted by
              February 25, 2000 it will lapse.

We are excited about Ambryx's prospects for success, and anticipate that your
contribution will substantially enhance our progress. I look forward to your
joining the Company, and to working with you as we develop our business.

Sincerely,


/s/  Paul A. Grayson
     Paul A. Grayson
     President and Chief Executive Officer

SIGNED AND AGREED TO:

/s/  Mark J. Zoller
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25 February 2000
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(Date)


cc: Dr. Lubert Stryer