By Jonathan Stempel

(Reuters) - A former Bristol-Myers Squibb Co finance executive on Monday pleaded guilty to an insider trading charge, admitting to buying stock options in a biotechnology company that the drugmaker was preparing to buy.

Robert Ramnarine, 46, admitted to one count of securities fraud for trading in Amylin Pharmaceuticals Inc options before Bristol-Myers agreed to buy that company last June for $5.3 billion, U.S. Attorney Paul Fishman in New Jersey said.

Federal prosecutors had last August charged Ramnarine with three counts of securities fraud.

They said he made $311,361 of illegal profit from August 2010 to July 2012 from options trading in Amylin and two other companies that Bristol-Myers sought to buy - Pharmasset Inc and ZymoGenetics Inc.

The U.S. Securities and Exchange Commission filed a parallel civil fraud case against Ramnarine.

Investigators said Ramnarine learned about the takeovers while working as a director and later as an executive director in Bristol-Myers' pension and savings investments office in Princeton, New Jersey.

They also said the East Brunswick, New Jersey resident did Internet searches on insider trading detection prior to some of his trades, including a review of an article titled "Ways to Avoid Insider Trading."

Ramnarine entered his plea before U.S. District Judge Anne Thompson in Trenton, New Jersey.

He faces a maximum of 20 years in prison and $5 million fine when he is sentenced on September 26. Ramnarine agreed to forfeit $311,361, and Fishman said the sentence can take into account his trades in Pharmasset and ZymoGenetics, as well as Amylin.

Douglas Jensen, a lawyer for Ramnarine, did not immediately respond to requests for comment.

Ramnarine had worked for Bristol-Myers for 15 years, the last of which as assistant treasurer for capital markets. His employment with the New York-based company ended last August after criminal charges were announced, court records show.

Bristol-Myers bought ZymoGenetics for $885 million in October 2010. Gilead Sciences Inc bought Pharmasset for about $11.2 billion in January 2012 after Bristol-Myers dropped out of talks.

The cases are U.S. v. Ramnarine, U.S. District Court, District of New Jersey, No. 12-mj-08121; and SEC v. Ramnarine in the same court, No. 12-04837.

(Reporting by Jonathan Stempel in New York; Editing by Bernard Orr)

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