MINOR AND TRACE STEROLS IN MARINE-INVERTEBRATES .14. ERGOSTA-5,7,9(11),22-TETRAEN-3-BETA-OL AND ITS 24-ZETA-ETHYL HOMOLOG, 2 NEW MARINE STEROLS FROM THE RED-SEA SPONGE BIEMNA-FORTIS

The steroidal components of a Red Sea sponge, Biemna fortis, were fractionated through reversed phase HPLC. and analyzed by a combination of physical methods, including high resolution GC./MS. and 360 MHz 1H‐NMR. The sponge contains five conventional Δ5‐sterols, 1a–c, 1e, 1g, which comprise about 25% of the mixture and 2,5% of gorgosterol 1h, a sterol never found before in Porifera. Three Δ5,7,22‐sterols were also present as major components in the mixture (∼70%): cholesta‐5,7,22‐trien‐3β‐ol 2a, ergosta‐5,7,22‐trien‐3β‐ol 2c and (24R)‐ethylcholesta‐5,7,22‐trien‐3β‐ol 2e whereas two new tetra‐unsaturated sterols were identified in minor amounts (2%): ergosta‐5,7,9(11),22‐tetraen‐3β‐ol 3c and 24ξ‐ethylcholesta‐5,7,9 (11), 22‐tetraen‐3β‐ol (3e or 3f). NMR. spectroscopy made possible the assignment of a 24R configuration for all the C(24) substituted sterols isolated in sufficient amount from the mixture. The possible symbiotic, dietary or biosynthetic origins of these sterols are discussed. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim