Minor and trace sterols in marine invertebrates. 1. General methods of analysis.

3beta-Hydroxy sterols occurring at a concentration of at least 0.001% of the sterol mixtures of Pseudoplexaura porosa and Plexaura homomalla have been fractionated using a series of refined techniques and subsequently analyzed using combined gas chromatography-mass spectrometry (GC-MS) in the development of a procedure for examining the minor and trace components of marine sterol mixtures. A total of 49 sterols were found which spanned a molecular weight range of 274 to 440. In addition delta4-3-keto analogs of cholesterol, 24-methylcholesterol and gorgosterol were found in the extracts of P. homomalla. Initial separation of various natural sterol-containing conjugates and free sterols was found to have a number of advantages. Fractional digitonin precipitation and alumina column chromatography were found to possess greater sterol separation abilities than previously recognized. Many of the minor sterols were found to possess novel structures including a series of short side chain sterols, 19-nor sterols, 5beta-stanols and 4-monomethyl sterols for which structure elucidation work is continuing.