Fastigilin B

3-Methyl-2-butenoic acid [(3S)-2,3,3aα,4,4a,5,7aα,8,9,9aα-decahydro-9β-hydroxy-3β,4aβ,8α-trimethyl-2,5-dioxoazuleno[6,5-b]furan-4α-yl] ester