**Exhibit 31.1**

 

**CERTIFICATIONOF THE CHIEF EXECUTIVE OFFICER PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002**

 

I, Christoph Westphal,certify that:

 

1. I have reviewed thisquarterly report on Form 10-Q of Sirtris Pharmaceuticals, Inc.;

 

2. Based on my knowledge,this quarterly report does not contain any untrue statement of a material factor omit to state a material fact necessary to make the statements made, inlight of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

 

3. Based on my knowledge,the financial statements, and other financial information included in thisquarterly report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report;

 

4. The registrant’s othercertifying officers and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f))  for the registrantand have:

 

a. Designed suchdisclosure controls and procedures, or caused such disclosure controls and proceduresto be designed under our supervision, to ensure that material informationrelating to the registrant, including its consolidated subsidiaries, is madeknown to us by others within those entities, particularly during the period inwhich this report is being prepared;

 

b. Evaluated theeffectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

 

c. Disclosed in thisreport any change in the registrant’s internal control over financial reportingthat occurred during the registrant’s most recent fiscal quarter (theregistrant’s fourth fiscal quarter in the case of an annual report) that hasmaterially affected, or is reasonably likely to materially affect, theregistrant’s internal control over financial reporting; and

 

5. The registrant’s othercertifying officers and I have disclosed, based on our most recent evaluationof internal control over financial reporting, to the registrant’s auditors andthe audit committee of registrant’s board of directors (or persons performingthe equivalent functions):

 

a. All significantdeficiencies and material weaknesses in the design or operation of internalcontrol over financial reporting which are reasonably likely to adverselyaffect the registrant’s ability to record, process, summarize and reportfinancial information; and

 

b. Any fraud, whether ornot material, that involves management or other employees who have asignificant role in the registrant’s internal control over financial reporting.

 
| Date: May 14, 2008                |   |   |
|----------------------------------------|--------|--------|
|                                   |   |   |
| /s/ Christoph Westphal                 |   |   |
| Christoph Westphal                     |   |   |
| President and Chief  Executive Officer |   |   |
| (principal executive  officer)         |   |   |

 

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