Sage Therapeutics Inc. sued Biogen Inc. on Friday, a week after the biotech giant made an unsolicited offer to acquire the smaller neuroscience company for about $469 million.

Biogen’s proposed acquisition comes after two difficult years of regulatory and clinical challenges, during which shares of Sage Therapeutics have fallen by more than 90%.

The proposed deal comes soon after Sage implemented a restructuring plan to focus on Zurzuvae’s launch in postpartum depression.

The $7.22-per-share deal for 89.8% of Sage is a 30% premium on the company's share price on Friday and is estimated by Reuters to be worth around $442 million. Biogen has a longstanding alliance in place with Sage and co-markets Zurzuvae (zuranolone), which is FDA-approved for post-partum depression (PPD).

Biogen proposes acquiring Sage Therapeutics for $7.22 per share, as analysts highlight the strategic value of Zurzuvae's success in postpartum depression.

Key Takeaways Sage Therapeutics reported that Biogen made an unsolicited offer to purchase all of the shares of the biopharmaceutical firm it doesn't already own.The bid of $7.22 per share was a 30% premium to Sage's closing price on Friday.