UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.  )

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o Preliminary Proxy Statement

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o Definitive Proxy Statement

þ Definitive Additional Materials

o Soliciting Material Pursuant to § 240.14a-12

PENWEST PHARMACEUTICALS CO.

(Name of Registrant as Specified In Its Charter)

TANG CAPITAL PARTNERS, LP

TANG CAPITAL MANAGEMENT, LLC

KEVIN C. TANG

PERCEPTIVE LIFE SCIENCES MASTER FUND LTD.

PERCEPTIVE ADVISORS LLC

JOSEPH EDELMAN

ANDREW D. LEVIN, M.D., PH.D.

(Name of Person(s) Filing Proxy Statement if Other Than the Registrant)

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On June 1, 2009, Kevin C. Tang, Managing Director of Tang Capital Partners, LP, sent the following letter to certain brokers, financial advisors and shareholders of Penwest Pharmaceuticals Co.:

Date: June 1, 2009

To: All Brokers, Financial Advisors, and Shareholders

Re: Penwest Pharmaceuticals Co. (PPCO)

All,

Tang Capital Partners, LP and its affiliates (“Tang Capital”) and Perceptive Life Sciences Master Fund Ltd. (“Perceptive”) are the two largest shareholders of Penwest

Pharmaceuticals Co. (“Penwest” or the “Company”) and together own approximately 42% of the Company’s outstanding common stock.

We have initiated a proxy contest for board representation and have sponsored three (3) very important shareholder proposals that we need to discuss with you and your clients.

Unfortunately, our ability to communicate with fellow shareholders directly has been significantly hampered by the Company’s refusal to obtain key shareholders lists even though we have requested that they do so.

It is imperative that we have the opportunity to speak with you and your clients about our solicitation efforts. Please contact me anytime, regardless of when. My information is below.

Kevin C. Tang, Managing Director

Tang Capital Management, LLC

4401 Eastgate Mall

San Diego, CA 92121

(858) 200-3830 Office

Email: kevin@tangcapital.com

www.penwestchange.com

Since the annual meeting is approaching quickly, please contact me ASAP.

Thank you very much for your time. I look forward to speaking with you

Sincerely,

Kevin C. Tang