Sullivan & Cromwell, Linklaters and Simpson Thacher & Bartlett have picked up mandates on the $5.9 billion hostile takeover bid launched earlier this week by German pharmaceuticals giant Merck for U.S. chemicals manufacturer Versum Materials.

The offer comes a month after U.S. manufacturer Entegris previously proposed to merge with Versum Materials to create a combined company with a market valuation of about $9 billion, according to Entegris.

Sullivan & Cromwell is advising regular client Merck. Los Angeles-based corporate partner Eric Krautheimer and New York healthcare partner Matthew Hurd are leading for the firm.

Linklaters is fielding a team advising Merck on financing, led by Frankfurt-based banking partner Neil George Weiand.

The deal reunites the Sullivan & Cromwell partners with Weiand, with whom they worked on pharma giant Bayer's takeover of U.S. competitor Monsanto in 2016 when Weiand was still at Allen & Overy.

Weiand is a longstanding loan adviser to Merck, having been involved in its €2 billion syndicated credit facility last June.

According to company press statements, Simpson Thacher is advising Versum Materials, while Wachtell, Lipton, Rosen & Katz is advising Entegris.

Other recent deals in the pharma sector include last year's £9.8 billion transatlantic joint venture between GlaxoSmithKline and Pfizer. Slaughter and May and Kirkland & Ellis are advising GSK, while Clifford Chance and Wachtell are advising Pfizer.

Ropes & Gray, Hogan Lovells and Shearman & Sterling also picked up mandates in December for GSK on its $5.1 billion acquisition of U.S. biopharmaceutical firm TESARO.