[(1R,2R,4R,6S,8R,11R,12S,13R,16R,17R,19S,20R)-17-acetyloxy-8-(furan-3-yl)-4,19-dihydroxy-1,9,11,16-tetramethyl-5,14-dioxapentacyclo[11.6.1.02,11.06,10.016,20]icos-9-en-12-yl] (E)-2-methylbut-2-enoate