The Carlyle Group on Monday announced one of the biggest buyout deals of 2011, teaming with fellow private equity firm Hellman & Friedman to purchase shares of publicly held Pharmaceutical Product Development for $3.9 billion.

The all-cash transaction valued Wilmington, N.C.-based PPD, which provides research and laboratory services to pharmaceutical companies, at $33.25 per share.

PPD’s board of directors has unanimously approved the merger and recommended that PPD’s shareholders adopt the agreement, which will result in PPD becoming a private company.

PPD employs more than 11,000 in offices across 44 countries. Its shares closed at $32.28 on Monday, a 25.8 percent increase above its opening price.