Under the terms of the agreement, Sepracor shareholders will receive $23 in cash for each share of Sepracor they own for a total transaction value of approximately $2.6 billion.

The investigation concerns whether the merger consideration is adequate and whether the Sepracor board of directors breached their fiduciary duties to Sepracor shareholders by agreeing to a strict no-solicitation provision and a $77.4 million termination fee that will all but ensure that no superior proposal will ever be forthcoming.

Sepracor is a research-based pharmaceutical company.