Minor and Trace Sterols in Marine Invertebrates. XII. Occurrence of 24 (R + S)‐isopropenylcholesterol, 24 (R + S)‐methylcholesta‐5, 25‐dien‐3β‐ol, and 24 (R + S)‐methylcholesta‐7, 25‐dien‐3β‐ol in the caribbean sponge, Verongia cauliformis

In addition to the two new sterols verongulasterol 11 and 25‐dehydroaplysterol 13 of Verongia cauliformis 3 ), 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 24 R ) 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.