3,6-Bis(acetyloxy)-7-hydroxy-3,6,9-trimethyl-2-oxo-2,3,3a,4,5,6,6a,7,9a,9b-decahydroazuleno[4,5-b]furan-4-yl 3-methyl-2-butenoate AIDS-137645 AIDS137645 NSC642603