Exhibit 10.50

Non-Employee Director Compensation Arrangements

Effective January 1, 2008, non-employee directors of Kosan
Biosciences Incorporated receive the following compensation for their service on the Board of Directors (the Board) and its committees. Except as otherwise noted, the stock option grants referenced below are made under the Companys
2000 Non-Employee Directors Stock Option Plan, as amended (the Directors Plan):

A. Non-Employee Chairman of the Board:



| | 1) | Annual Cash Retainer of $40,000
| | -- | -------------------------------



| | 2) | Annual Stock Option Grant to purchase 15,000 shares1of Common Stock (to be automatically granted one day following each years annual meeting of stockholders) that will vest one day before the annual meeting of stockholders
subsequent to the date of grant.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 3) | Meeting fees: $1,500 for each Board meeting attended in person and $750 for each Board meeting attended by phone.
| | -- | -----------------------------------------------------------------------------------------------------------------

B. Non-Employee Directors:



| | 1) | Annual Cash Retainer of $20,000
| | -- | -------------------------------



| | 2) | Annual Stock Option Grant to purchase 10,0001shares of Common Stock (to be automatically granted one day following each years annual meeting of stockholders) that will vest one day before the annual meeting of stockholders subsequent to the date of grant.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 3) | Meeting fees: $1,500 for each Board meeting attended in person and $750 for each Board meeting attended by phone.
| | -- | -----------------------------------------------------------------------------------------------------------------

New Non-Employee Directors- One Time Grant:

Upon each non-employee director becoming a director, he or she will be automatically granted on the date on which such person first becomes a director, a stock option to purchase 20,000 shares of common stock that vests over four years.

C. Non-Employee Chairman of the Audit Committee, Compensation Committee and Corporate Governance and Nominating Committee:



| | 1) | Annual Committee Chairman Cash Retainer of $5,000
| | -- | -------------------------------------------------



| | 2) | Annual Committee Chairman Stock Option Grant to purchase 2,000 shares of Common stock (to be automatically granted one day following each years annual meeting of stockholders)
that will vest one day before the annual meeting of stockholders subsequent to the date of grant.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | 3) | Meeting fees: $1,500 for each Committee meeting attended in person and $750 for each Committee meeting attended by phone.
| | -- | -------------------------------------------------------------------------------------------------------------------------

D. Non-Employee Director serving on the Audit Committee, Compensation Committee and Corporate Governance and Nominating Committee:



| | 1) | Annual Committee Member Stock Option Grant to purchase 1,000 shares of Common stock (to be automatically granted one day following each years annual meeting of stockholders)
that will vest one day before the annual meeting of stockholders subsequent to the date of grant.
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



|1 | The annual option grants are comprised of a stock option to purchase 5,000 shares of Common Stock granted under the
Directors Plan for so long as a balance remains under such plan and a stock option to purchase the balance of the shares of Common Stock under the Companys 2006 Equity Incentive Plan.
|- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| | 2) | Meeting fees: $1,000 for each Committee meeting attended in person and $500 for each Committee meeting attended by phone.
| | -- | -------------------------------------------------------------------------------------------------------------------------

E. Non-Employee Chairman of the Strategic Advisory Committee:



| | 1) | Annual Chairman Cash Retainer of $15,000
| | -- | ----------------------------------------



| | 2) | Meeting Fees:
| | -- | -------------



| | a. | $2,500 for each Strategic Advisory Committee meeting attended in person and lasting 3 4 hours and $1,250 for each Strategic Advisory Committee
meeting attended by phone and lasting 3 4 hours;
| | -- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | b. | Pro-rata (based on $2,500/day) for each Strategic Advisory Committee meeting attended and lasting < 4 hours whether attended in person or by phone
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------

F. Non-Employee Director serving on the Strategic Advisory Committee:



| | 1) | Meeting Fees:
| | -- | -------------



| | a. | $2,000 for each Strategic Advisory Committee meeting attended in person and lasting 3 4 hours and $1,000 for each Strategic Advisory Committee
meeting attended by phone and lasting 3 4 hours;
| | -- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | b. | Pro-rata (based on $2,000/day) for each Strategic Advisory Committee meeting attended and lasting < 4 hours whether attended in person or by phone
| | -- | --------------------------------------------------------------------------------------------------------------------------------------------------

G. Non-Employee Director serving on the Financing Committee:

There shall be no stock or cash compensation paid to members of the Financing Committee.