Tetraphase shares unchanged on first day of trading after $75 million IPO

By Robert Weisman, Globe Staff

Tetraphase Pharmaceuticals Inc. stock closed unchanged at $7 a share on its first day of trading on the Nasdaq exchange Wednesday after the Watertown biotechnology start-up raised $74.9 million in an initial public offering.

Tetraphase, which is working on technology to create antibiotics for abdominal and urinary tract infections, priced its offering of 10.7 million shares of common stock at $7 a share. That was below the $10 to $12 price range initially specified in the company’s registration statement.

Another Watertown biotechnology company, Enanta Pharmaceuticals Inc., is also expected to price its shares this week in what could be a $60 million IPO. Enanta is developing drugs to treat the hepatitis C virus.