PARIS, Aug 17 (Reuters) - French healthcare company Sanofi has agreed to buy U.S. company Principia Biopharma for around $3.7 billion, the companies said on Monday, strengthening Sanofi's presence in research and development (R&D) areas.

Sanofi said it would buy all of the outstanding shares of Principia for $100 per share in cash, representing an aggregate equity value of approximately $3.68 billion on a fully diluted basis.

"This acquisition advances our ongoing R&D transformation to accelerate development of the most promising medicines that will address significant patient needs," said Sanofi chief executive Paul Hudson.

(Reporting by Sudip Kar-Gupta; Editing by Jacqueline Wong)