Amgen (Nasdaq:AMGN) announced that it would purchase the San Carlos, California–based ChemoCentryx (Nasdaq:CCXI) for $52 per share in cash, which equates to a total of approximately $3.7 billion. The centerpiece of the proposed acquisition is Tavneos (avacopan), which scored FDA approval last year for the adjunctive treatment of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. The disease…