OSAKA, Japan ( TheStreet) -- Japanese drugmaker Dainippon Sumitomo Pharma confirmed it has reached an agreement to buy Sepracor ( SEPR) for $23 a share, or $2.6 billion, in an effort to help sell its Lurasidone drug in the U.S. Shares of Sepracor closed Thursday at $22.80, after rising on rumors of a potential deal. Sepracor closed Tuesday at $18.03, making the acquisition premium 27.6%. Dainippon plans to file for U.S. marketing approval next year of its experimental schizophrenia drug Lurasidone. The acquisition is seen as a way to gain access to Sepracor's sales force. Various earlier reports had put the acquisition price at $2.7 billion. The boards of both companies have approved the deal. Under the terms of the definitive agreement, Dainippon will begin a tender offer no later than Sept. 15 for Sepracor shares at $23 a share. "Sepracor has pursued growth through development of its unique pipeline and introduction of innovative pharmaceutical products to the market, a strategy that fits perfectly with our management philosophy," said Dainippon President Masayo Tada, in a statement. "We expect that Sepracor will become a 'Center of Excellence' for DSP in the U.S., and will make a significant contribution to DSP both as a commercialization infrastructure for our self-developed products and as a strategically important base for business development." -- Reported by Joseph Woelfel in New York . Follow TheStreet.com on Twitter and become a fan on Facebook.