Sanofi is in talks to buy Flexion Therapeutics, a Boston-area biotech with its lead product now awaiting FDA approval, for more than $1 billion in cash, according to a source close to the deal. | Sanofi is in talks to buy Flexion Therapeutics, a Boston-area biotech with its lead product now awaiting FDA approval, for more than $1 billion in cash, according to a source close to the deal.