Carlyle Group is in exclusive talks to buy Pharmaceutical Product Development Inc. (Nasdaq: PPDI), a clinical research company, five people with knowledge of the discussions told Bloomberg news on Tuesday.

Reuters also reported that a deal is in the works.

The news sparked PPD shares to a new 52-week high of $33.07 in heavy trading. More than 5 million shares traded hands. PPD closed at $32.28.

Shares soared 17 percent higher on Monday to a close of $31.51 before the sales reports broke on Tuesday. More than 4 million shares were traded.

Carlyle topped private-equity firms including Blackstone Group LP (BX), KKR & Co. and Hellman & Friedman LLC that bid or expressed interest, said two of the people, who declined to be identified because the process was private. Most bids were between $33 a share and $38 a share, or as much as $4.3 billion, said the people. PPD rose 31 cents to $31.82 at 10:05 a.m. in Nasdaq Stock Market trading, giving the company a value of about $3.63 billion.

PPD, which was founded by Fred Eshelman who still chairs the company, said last month that the company was looking for ways to enhance shareholder value.

“While the company generally has a policy of not commenting on speculation,” Eshelman said on July 17, “we want to assure our customers and employees that the company remains focused on executing its long-term business strategy. We are absolutely dedicated to performing for our customers and committed to executing the important research programs that they have entrusted to us.”

PPD shares had closed at $27.86 on July 15. Rumors of a PPD sale broke two days later, sparking the trading of 7.8 million shares on July 18.

A purchase in the middle of the $3.6-$4.3 billion range for Wilmington, NC-based PPD “would be an attractive deal for shareholders,” David Windley, an analyst at Jefferies & Co. in Nashville said in an e-mail. Going private might allow the drug research company “to explore more complex deal structures with clients,” he said

Carlyle is talking to other private-equity firms about joining it in an offer for the company, one person said. Rival bidders were informed last week that another firm had been given exclusivity to negotiate with PPD, said another person. Morgan Stanley is advising PPD, according to the people. The talks between Carlyle and PPD may still collapse.

Spokesmen for Carlyle, Morgan Stanley, Blackstone and KKR declined to comment. Hellman & Friedman and PPD didn’t return calls seeking comment.

Largest Deal

The acquisition would be the largest for Carlyle since announcing the $3.9 billion purchase of telecommunications- equipment maker CommScope Inc. in October. Washington-based Carlyle, which has announced deals valued at $10 billion in the last 12 months, is selling old investments and entering new ones as the company plans a formal process for its initial public offering. Carlyle announced today it would sell Insight Communications Co., a six-year investment, to Time Warner Cable Inc. for about $3 billion.

Pharmaceutical firms were not given the option of bidding on PPD, said two people familiar with the matter. Only private- equity funds were allowed to bid on the asset, they said.

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