Paul, Weiss, Rifkind, Wharton & Garrison is representing Bioverativ Inc., a maker of hemophilia drugs, in its $11.6 billion sale announced Monday to French pharmaceutical giant Sanofi S.A.

The deal is another high-profile engagement for Paul Weiss' global M&A head Scott Barshay, who made a rare move from Cravath Swaine & Moore in a 2016 lateral hire The American Lawyer reported at the time “instantly reshuffl[ed] the decks of top deal advisory work.”

It is the second Bioverativ transaction in as many years that Barshay has worked on. His online biography page on Paul Weiss' website states that he represented Biogen Inc. in its $5 billion spinout of Bioverativ. That deal was announced the month after Barshay joined Paul Weiss and was completed in February 2017 last year.

Biogen, Bioverativ's former parent company, is also a client of Mark Greene, the head of Cravath's corporate department. Cravath represented Biogen in a $1.25 billion settlement in January 2017 to license intellectual property from Danish biopharmaceutical company Forward Pharma A/S.

While departures from Cravath's lockstep partnership remain exceedingly rare, many in the legal market have watched Barshay's move with interest because of broader questions it might answer: Will Cravath, like Paul Weiss, modify its lockstep compensation system to discourage top-flight partners from leaving? And how will Barshay's performance at Paul Weiss impact other partners considering leaving lockstep firms?

“There sure are a lot of naysayers who are quick to say, 'You've got a good client following because you're at Cravath,” said New York-based legal recruiter Alisa Levin. “But if someone else [at Cravath] was on the fence or thinking about leaving, seeing the real demonstrable success Scott has, it puts a little more pressure on the scale on that side to leave Cravath.”

Waltham, Massachusetts-based Bioverativ, whose chief legal officer Andrea DiFabio was previously a senior in-house lawyer at Biogen, is far from the first client with Cravath ties that Barshay has represented at Paul Weiss.

Barshay is currently representing longtime Cravath client and chipmaker Qualcomm Inc. in a proposed $103 billion hostile takeover bid by rival Broadcom Ltd. In 2016, Barshay advised Qualcomm in its ongoing $47 billion acquisition of NXP Semiconductors NV, which recently gained the approval of European regulators.

Almost a year ago, Barshay also led a Paul Weiss team advising Kraft Heinz Food Co. in its ultimately aborted $143 billion takeover bid for fellow food industry giant Unilever. While at Cravath, Barshay led a team from the firm advising H.J. Heinz Co. on its $40 billion merger in 2015 with Kraft Foods Group Inc.

Calls to Barshay, Cravath's Greene and Bioverativ's DiFabio were not returned by the time of this story. Barshay is representing Bioverativ with Jeffrey Marell, co-head of the M&A practice at Paul Weiss, while Weil, Gotshal & Manges corporate chair Michael Aiello and M&A partner Sachin Kohli are leading a team from the firm advising Sanofi. The deal is expected to close within the next three months.

In the broader M&A market, Cravath and Paul Weiss both slipped last year in Bloomberg's league table rankings for legal advisers.

Cravath ranked No. 10 in 2017 in deals advised on by value, with a total of 76 transactions worth roughly $232 billion, good for 6.9 percent of the year's deal market. The year prior, Cravath ranked third among legal advisers, with a 14.7 percent share of the deal market.

Paul Weiss, which came in at No. 15 in Bloomberg's 2016 year-end M&A table, fell out of the top 20 advisers when ranked by deal volume in 2017. (As previously noted by The American Lawyer, league tables can be an imperfect metric for measuring M&A prowess.)

Levin, a principal at recruiting firm Greene-Levin-Snyder, said that Barshay's departure from Cravath and his subsequent success at Paul Weiss is unlikely to change Cravath's view of the benefits of a lockstep compensation system.

“Should they continue to lose top-performing partners, that is a much more dramatic event,” Levin said. “But it seems they're staying true to their ethos, their culture and their identity.”

The Bioverative transaction is also good to shareholders of the publicly traded company. Sanofi said it would pay $105 in cash for each share of Bioverativ, a 64 percent premium to Bioverativ's closing price on Jan 19. The proposed deal isn't the only M&A engagement generating work this week for Big Law.

Summit, New Jersey-based biopharmaceutical company Celgene Corp. has turned to Hogan Lovells and Proskauer Rose to advise on its $9 billion bid for Juno Therapeutics Inc., a Seattle-based cancer drug maker being advised by Skadden, Arps, Slate, Meagher & Flom.

The deal, announced Monday and expected to close in the first quarter of 2018, comes two weeks after Hogan Lovells grabbed a lead role counseling Celgene on its proposed $1.1 billion buy of Impact Biomedicines, a San Diego-based blood disease biotechnology company being advised Latham & Watkins. That transaction, also slated to close within three months, could be worth up to $7 billion if Impact hits certain milestones.