Amgen Inc., the Thousand Oaks-based biotech firm, tapped Latham & Watkins for a $4.5 billion offering of investment-grade notes. Shearman & Sterling represented the syndicate of 18 underwriters, led by Morgan Stanley.

The drugmaker will use the proceeds to repurchase shares of a subsidiary, ATL Holdings Limited, as well as repay certain borrowings under its term loan. Amgen undertook those financings to pay for its October 2013 acquisition of San Francisco-based Onyx Pharmaceuticals, a $9.7 billion transaction.

For that deal, its largest ever, Amgen received legal counsel from Sullivan & Cromwell, as well as antitrust advice from McDermott Will & Emery. Certain financing issues were fielded by Latham. Shearman & Sterling advised the underwriters for that transaction as well.

The Shearman & Sterling team advising the underwriter group included partners John Wilson in San Francisco, Alan Seem, Larry Crouch and Richard Hsu in Palo Alto; counsel Eileen O’Pray and Daniel Stellenberg in Palo Alto and Emily Griffen in San Francisco; and associates Nathan Mee and Scott Lucas in San Francisco, Jennifer Morton and Jenny Ding in New York, and Zheng Bao and Alice Townes in Palo Alto.

The Latham team advising Amgen included partners Charles Ruck in Orange County and New York and Gregory Rodgers in New York, along with associates Charles Cassidy in Washington, D.C., and Michael Raine out of New York.

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