Sanofi is turning up the heat on its acquisition target, US biopharmaceuticals producer Medivation, but the strategy doesn’t seem to be working. Last week, the French drugmaker said it had taken its case directly to Medivation shareholders, as threatened earlier, and swore dire consequences if the company’s board again rejected its offer – which it promptly did.

In a letter dated May 4, Sanofi CEO Olivier Brandicourt informed the Medivation directors that in “extensive conversations with your shareholders,” the company had registered “overwhelming support” for the proposed deal.

If the board still refused to negotiate, Sanofi suggested that, with the shareholders’ backing, it could have its directors removed. Without news of the Sanofi proposal, Olivier said “Medivation shares would be trading in the $30's.” The California firm’s stock traded at $27 per share less than three months ago, he reminded the board, noting that “our proposal is almost a 100% premium to that price” and over a 50% premium to average trading prices prior to the emergence of takeover rumors.

In Sanofi’s first open letter to Medivation, which it released on Apr. 28, Brandicourt said the French company was prepared to offer $52.50 per share for the US prostate cancer drug developer, valuing it at around $9.3 billion.

In his latest communication, the Sanofi chief said, “An immediate engagement would be in the best interests of your shareholders as it would enable them promptly to realize substantial and certain value, while minimizing the disruption to your organization.” He reminded the board also that its shareholders have the ability to act at any time by written consent to remove and replace the directors.

Medivation’s response was that Sanofi's letter “simply restates an inadequate proposal” that undervalues the company, its leading oncology franchise and innovative late-stage pipeline. The brief statement added that the board "believes the execution of Medivation's business plan will deliver value to its stockholders that is far superior to Sanofi's proposal."

Analysts continue to be skeptical of the Sanofi “saber rattling.” Some said they thought the tactics might work if Medivation were a troubled company, which with a major drug on the market it is not. The consensus seemed to be that the US company could afford to bide its time.

Market speculation sees other international drug companies interested in the US cancer specialist. According to the news agency Reuters, Pfizer has approached Medivation. Other names thrown into the hat by analysts include AstraZeneca and Roche.