Time is running out for Pfizer’s offer to buy Durham-based Icagen.

Pfizer (NYSE: PFE) said Thursday before the markets opened that it had extended its $6 per share offer through Sept. 1. The deadline had been midnight, Aug. 31.

Some Icagen (Nasdaq: ICGN) investors have argued that the offer is too low. Icagen’s board and management have spoken out in favor of the deal.

Pfizer said last week that it would not raise the offer.

According to Pfizer, as of Thursday morning the company held rights to 107,431 shares fewer than necessary to gain control of Icagen. The 5.1 million shares Pfizer owns and has had tendered to it represent some 49 percent of Icagen shares.

“All other terms and conditions of the tender offer remain unchanged,” Pfizer said. “If all of the conditions to the tender offer are satisfied, Eclipse [a subsidiary of Pfizer] intends to complete the tender offer by promptly accepting for payment all Icagen shares validly tendered and not validly withdrawn in the tender offer. Following completion of the tender offer, Pfizer and Eclipse intend to complete the acquisition of Icagen through a merger under Delaware law, subject to customary conditions. Icagen shareholders who do not tender their shares of Icagen common stock in the tender offer will not receive payment for their shares until the completion of the merger.”

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