(3R-(3R*,3AS*,4S*,6R*,10S*,11AR*))-2-Methylpropanoic acid 2,3,3a,4,5,6,7,10,11,11a-decahydro-3,6,10- trimethyl-2,7-dioxo-6,9-epoxycyclodeca(b)furan-4-yl ester 28644-87-3 Zexbrevin A