Bain Capital is nearing a deal to buy Mitsubishi Chemical Group Corp.’s pharmaceutical unit, people familiar with the matter said, adding to a dealmaking boom in Japan.

U.S. private equity firm Bain Capital has bought Mitsubishi Tanabe Pharma in a deal worth 510 billion yen ($3.4 billion), saying it was encouraged by prospects of regulatory change for Japan's drug industry.

Following rumblings of a private equity bidding war late last year, Bain Capital has emer | Bain Capital is laying out 510 billion Japanese yen ($3.3 billion) to acquire Mitsubishi Tanabe Pharma in a carve-out transaction from its parent Mitsubishi Chemical Group.