INVESTIGATION OF 4-METHYL STEROLS FROM CULTURED DINOFLAGELLATE ALGAL STRAINS

The marine dinoflagellates Prorocentrum micans, Gonyaulax polyedra, Gy mnodinium sp., and Alexandrium tamarense, collected from the Adriatic Sea during red-tide blooms, were cultured to investigate the 4-methyl sterol constituents. To ascertain a possible influence of cell age on the 4-methyl sterol content, for one strain (Gymnodinium sp.) we inves tigated the composition of these constituents at exponential and stati onary growing phases. The lipid material extracted with acetone from t he lyophilized algal samples was fractionated by thin-layer chromatogr aphy. The 4-methyl sterols recovered from the layer were converted int o the corresponding OTMS derivatives. Nine of 11 constituents were ide ntified by gas chromatography and gas chromatography-mass spectrometry ; only two minor constituents were characterized by their gas chromato graphic parameters. All free methyl sterols identified in the algal sa mples had been detected previously in various dinoflagellates. The 4-m ethyl sterol fractions generally contained very few constituents. Exce pt for the Gymnodinium sp. sample, collected at the exponential growin g phase (GyD2 exp), which contains 4,24-dimethylcholestan-3-ol as a un ique constituent, dinosterol was the major component. Moreover, 4,24-e thylcholestan-3-ol was also an important constituent of both Prorocent rum and Gonyaulax strains, whereas considerable amounts of dinostanol characterized all the Gymnodinium sp, strains. In addition, the latter contained several minor constituents such as 4-methylcholestan-3-ol, 4,24-dimethylcholesta-22-en-3-ol, and 4-methyl-24-ethylcholestan-3-ol. 4-Methyl-24-methylene-cholestan-3-ol was a constituent of the Gymnodi nium sp. sample, collected at the stationary growing phase (GyD2 stat) only, whereas 4-methylgorgostanol was identified only in the Alexandr ium tamarense Gt4 strain. Except for 4-methyl-24-ethylcholesta-8(14)-e n-3-ol, all the methyl sterol constituents from our algae show a satur ated polynuclear system. The pathways by which side-chain modification s occur in dinoflagellate 4-methyl sterols are considered and a map of the fragmentation pattern of the trimethylsilyl-4-methyl sterols unde r electronic impact is also reported.