Affymax Inc. said Tuesday it obtained a commitment from institutional investors to purchase approximately $42 million of its common stock in a private placement.

Palo Alto-based Affymax (NASDAQ:AFFY) said it will sell about 2.8 million newly issued shares of its common stock at a purchase price of $11.25 per share. In a separate purchase agreement, Affymax will sell 652,262 newly issued units at a purchase price of $15.33 per unit, with each unit consisting of one share of common stock and one warrant to purchase 0.65 of a share of common stock. The warrants are immediately exercisable at $16.78 per share and will expire five years from the date of issuance.

The company’s stock closed the day Friday at $15.60.

The financing was led by ProQuest with participation by existing investors, New York-based Sprout Group and Bessemer Venture Partners, which has an office in Menlo Park; and new investor, San Francisco-based Biotechnology Value Fund.