Sanofi SA said Monday it would buy hemophilia drugmaker Bioverativ Inc. for more than $11.5 billion, as the French drugmaker looks to clinch a big deal while it braces for generic competition for its top-selling product.

On Sunday, The Wall Street Journal reported that the deal would value the former Biogen Inc. unit at $105 a share, according to people familiar with the matter. The price would represent a premium of about 63% to where Bioverativ closed trading Friday.

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