MINOR AND TRACE STEROLS IN MARINE-INVERTEBRATES .12. OCCURRENCE OF 24(R+S)-ISOPROPENYLCHOLESTEROL, 24(R+S)-METHYLCHOLESTA-5,25-DIEN-3-BETA-OL, AND 24(R+S)-METHYLCHOLESTA-7,25-DIEN-3-BETA-OL IN THE CARIBBEAN SPONGE, VERONGIA-CAULIFORMIS

In addition to the two new sterols verongulasterol 11 and 25‐dehydroaplysterol 13 of Verongia cauliformis3), which were reported earlier [2] [3], the minor and trace sterols of this sponge include five new sterols listed in the title (with the exception of the known 24 S‐methyl‐cholesta‐5, 25‐dien‐3β‐ol (codisterol, 1b). The isolation of the 24(R)‐epimer of codisterol is of interest, as this compound is a possibly biosynthetic precursor for aplysterol 12, 25‐dehydroaplysterol 13, and verongulasterol 11 (all 24R) which occur in the same sponge [2]. A partial synthesis from fucosterol (4) of 24 (R + S)‐isopropenylcholesterol (9), and of 24‐isopropylcholesterol (10) is described. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim