The lack of new information about Sanofi Aventis' reported interest in acquiring Genzyme could mean the two sides have begun talks, according to Sanford Bernstein analyst Geoffrey Porges.

"The best guess is probably that these discussions are focused on enhancing Sanofi's understanding of Genzyme's businesses, rather than on deal negotiation," he said in a note to clients. "It also seems feasible that the two parties have entered into a confidentiality agreement or are in the process of negotiating one."

After an initial flurry of leaks to the media, in which the French drugmaker was reported to have offered $69 a share to acquire Genzyme, a Cambridge, Massachusetts-based biotechnology company, both sides have gone silent.

Porges said it would be consistent with prior acquisitions in the sector if Sanofi made some initial advances to Genzyme, was rebuffed, and then elected to use hostile tactics to force Genzyme to the negotiating table.

"Rather than making a public tender offer, one may speculate that they elected to use leaks to the press as a way of achieving this end without formally committing to a specific tender price," he said.

As the news flow has dried up, Genzyme shares have fallen back amid concern a deal might not get done. On Friday the shares were up 18 cents at $66.08, well below a 52-week high of $70.97 on July 29.

"I think the nervousness on the part of current shareholders is unfounded but is probably the result of deliberate tactics by advisers to Sanofi," Porges said. "I doubt if it will work, but in the current market institutions are understandably skittish."

He said the press leaks were probably initiated by Sanofi and its bankers as a way of locking in a premium to Genzyme's share price and putting pressure on Genzyme to enter into serious negotiations by appealing directly to the shareholder base.

He noted, however, that even cases in which a majority shareholder makes a "hardball" offer -- and Sanofi is not a majority shareholder in Genzyme -- the price can change significantly if not enough shareholders find it enticing.

As an example, he points to the acquisition of Genentech by majority shareholder Roche Holding, which was forced to raise its initial offer of $89 a share to $95.

A Reuters poll of 30 Genzyme shareholders conducted in early August indicated that five were willing to sell for between $70 and $74 a share, 14 were willing to take $75 to $79, and 11 wanted $80 or more. Among those wanting $80 or more, five said they would insist on at least $85.

Based on an analysis of seven relevant prior cases, Bernstein said that once a hostile approach has been made, a process is triggered that leads to an acquisition of the target in less than a year, at a price that is 10 % to 15 % above the initial offer, or 20 % to 25 % higher if a second bidder emerges or large shareholders hold out.

Assuming $69 a share was Sanofi's initial offer, that would imply a price of $76-$79, or $83-$86 if a second bidder emerges, he said.

"Our review of prior comparables suggests that Genzyme shares offer compelling upside relative to their downside risk in the next six to eight months, based on the pattern of hostile deals being completed at a premium to an initial offer, regardless of whether additional bidders emerge," he said.