ELIXIR PHARMACEUTICALS, INC. SENIOR EXECUTIVE INCENTIVE BONUS PLAN

Exhibit 10.47

ELIXIR PHARMACEUTICALS, INC.

SENIOR EXECUTIVE INCENTIVE BONUS PLAN

This Senior Executive Incentive Bonus Plan (the “Incentive Plan”) is intended to provide an incentive for superior work and to motivate eligible executives of Elixir Pharmaceuticals, Inc., a Delaware corporation, having its principal place of business at 12 Emily Street, Cambridge, Massachusetts 02139 (the “Company”) toward even higher achievement and business results, to tie their goals and interests to those of the Company and its stockholders and to enable the Company to attract and retain highly qualified executives. The Incentive Plan is for the benefit of Covered Executives (as defined below).

From time to time, the Compensation Committee of the Board of Directors of the Company (the “Compensation Committee”) may select certain key executives (the “Covered Executives”) to be eligible to receive bonuses hereunder.

The Compensation Committee shall have the sole discretion and authority to administer and interpret the Incentive Plan.

(a) A Covered Executive may receive a bonus payment under the Incentive Plan based upon the attainment of company, departmental or individual performance targets which are established by the Compensation Committee and relate to financial and operational metrics and clinical milestones with respect to the Company (the “Performance Goals”), including the following: revenues, expense levels, cash flow, clinical, regulatory, business development, and financing milestones and developments.

(b) Except as otherwise set forth in this Section 4(b): (i) any bonuses paid to Covered Executives under the Incentive Plan shall be based upon objectively determinable bonus formulas that tie such bonuses to one or more performance targets relating to the Performance Goals, (ii) bonus formulas for Covered Executives shall be adopted in each performance period by the Compensation Committee and communicated to each Covered Executive at the beginning of each bonus period and (iii) no bonuses shall be paid to Covered Executives unless and until the Compensation Committee makes a determination with respect to the attainment of the performance objectives. Notwithstanding the foregoing, the Company may adjust bonuses payable under the Incentive Plan based on achievement of individual performance goals or pay bonuses (including, without limitation, discretionary bonuses) to Covered Executives under the Incentive Plan based upon such other terms and conditions as the Compensation Committee may in its discretion determine.

(c) Each Covered Executive shall have a targeted bonus opportunity for each performance period.

(d) The payment of a bonus to a Covered Executive with respect to a performance period shall be conditioned upon the Covered Executive’s employment by the Company on the last day of the performance period; provided, however, that the Compensation Committee may make exceptions to this requirement, in its sole discretion, including, without limitation, in the case of a Covered Executive’s termination of employment, retirement, death or disability.

The Performance Goals will be measured at the end of each fiscal year after the Company’s financial reports have been published. If the Performance Goals are met, payments will be made within 30 days thereafter, but not later than March 15.

The Company reserves the right to amend or terminate the Incentive Plan at any time in its sole discretion.

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