Canada's Valeant Pharmaceuticals Inc. made a bid to acquire biopharmaceutical company Cephalon Inc. for $5.7 billion in cash, and said it would press to install a slate of hand-picked directors to its would-be quarry's board next week.

Valeant resorted to airing out its proposed takeover bid after Cephalon's board didn't engage in talks after a series of behind-the-scene overtures.

The proposal by Mississauga, Ontario-based Valeant amounts to $73 a share and represents a 27 percent premium over Frazer, Penn.-based Cephalon's closing price on Monday.

Valeant said it intends to seek shareholder approval to replace Cephalon's board with its own nominees.

It also noted that it has received a letter of financing from Goldman Sachs & Co., which it would use to fully fund a Cephalon acquisition.

News of the offer sent Cephalon shares surging 24 percent, or $14.14, to $72.89 in aftermarket trading. The stock ended the regular session up $1.18, or 2.1 percent, to $58.75.

In a statement, Valeant Chairman and CEO J. Michael Pearson accused Cephalon of being unwilling to engage in discussions over the proposed offer in a timely manner.

"Given the importance of this transaction proposal to shareholders of both companies, and given that Cephalon's management continues to pursue strategies that in our view reduce the value of a merged entity, we have decided to make our proposal public," he said.

Pearson also suggested Valeant might be willing to find "additional value" if it is allowed to conduct due diligence by Cephalon.

Cephalon issued a statement late Tuesday saying it intends to consider the unsolicited offer and respond in due course.

Valeant spilled the details on its corporate courtship in letters marked "private and confidential" that were addressed to Cephalon CEO Kevin Buchi and other board members.

In three letters dated between March 18 and Tuesday, Pearson implored Buchi to consider the offer, noting the proposal has the unanimous support of Valeant's board.

But in a letter dated last Friday, Pearson expressed disappointment over Buchi saying he is confident the Cephalon board would consider the offer too low to warrant engaging in talks with Valeant.

Pearson also took issue with Cephalon's announcement last week that it reached a deal to acquire Gemin X Pharmaceuticals Inc. for $225 million in cash. On Monday, Cephalon announced plans to make a takeover bid for Australian biopharmaceutical company ChemGenex in a deal that values all the company's shares and options at about $231 million.

Still, Pearson offered to discuss an alternative proposal: $2.8 billion, or $37 a share, to buy just Cephalon's non-oncology related assets.

In Tuesday's letter, it was clear Cephalon's board wouldn't meet to discuss the proposed bid before next week.

Pearson suggested that enough time had already passed.

"It appears to us that you maybe delaying your response in order to put up more barriers for us to complete our offer, and in the process, costing your shareholders significant value," Pearson wrote.