BIOSYNTHETIC-STUDIES OF MARINE LIPIDS .42. BIOSYNTHESIS OF STEROID AND TRITERPENOID METABOLITES IN THE SEA-CUCUMBER EUPENTACTA-FRAUDATRIX

The saponins, conjugated sterols, and free sterols of the sea cucumber Eupentacta fraudatrix were examined. A total of 85 steroids, twelve o f them new, were identified in the free sterol, sulfated sterol, and s terol-xyloside fractions. The free sterol fraction contained 4alpha,14 alpha-dimethylcholest-9(11)-en-3beta-ol (6) and 14alpha-methylcholest- 9(11)-en-3beta-ol (7) together with 18 minor sterols. Examination of t he aglycone moieties of the sterol-beta-xyloside fraction afforded 31 different sterols. Cholestan-3beta-ol (15) and 24-methylcholesta-7,22- dien-3beta-ol (20) were the major sterols in this group. Cholestanol s ulfate (74) and cholesterol sulfate (64) were identified as the major components among the 34 different sterol sulfates present. Finally, cu cumariosides G1 (1), C1 (2), C2 (3), H (4), and G2 (5) were isolated f rom the saponin fraction. Radiolabeling experiments indicated that the re are two pathways of sterol biosynthesis in E. fraudratix. The first involves transformation of squalene to produce lanosta-9(11),24-dien- 3beta-ol (parkeol) which is subsequently demethylated to form 4alpha,1 4alpha-dimethylcholest-9(11)-en-3beta-ol (6) and 14 alpha-methylcholes t-9(11)-en-3beta-ol (7). The second proceeds through squalene to lanos terol which is further metabolized to produce the triterpene saponins, 5alpha-cholest-7-en-3beta-ol (19) and its xyloside (49).