5α‐24‐Norcholestan‐3β‐ol and (24Z)‐Stigmasta‐5,7,24(28)‐trien‐3β‐ol, Two New Marine Sterols from the Pacific Sponges Terpios zeteki and Dysidea herbacea

The steroidal components of 2 marine sponges, Terpios zeteki (from Hawaii) and Dysidea herbacea (from Australia) were fractionated through a combination of chromatographic methods, including reversed phase HPLC., and were analyzed by a combination of physical methods, including high resolution GC.‐MS. and 360 MHz 1H‐NMR. T. zeteki contains 6 conventional 5α‐stanols which comprise 91% of the sterol mixture, and traces (0.5%) of a new C26 sterol, 5α‐24‐norcholestan‐3β‐ol. Minor amounts of conventional Δ5‐sterols (6.5%) and of a single Δ4‐3‐ketosteroid (1.5%) were also present. In contrast, the Australian sponge (D. herbacea) contains 3 Δ5,7‐sterols which comprise 1.5% of the sterol mixture, and one new C29 sterol, (24 Z)‐stigmasta‐5,7,24(28)‐trien‐3β‐ol, as the major component (75%). In addition, minor amounts of conventional 5α‐stanols (0.5%), Δ5‐sterols (5%) and 5α‐Δ7‐sterols (18%) were present in this complex sterol mixture. The possible dietary or endosymbiotic origins of these sterols are discussed.