Sterols of four dinoflagellates from the genus Prorocentrum

The compositions of 4-desmethyl sterols and 4-methyl sterols in four species of marine dinoflagellates of the genus Prorocentrum (viz., P. micans Ehrenberg, P. minimum (Pavillard) Schiller, P. balticum (Lev.) Lemm and P. mexicanum Tafall) were identified by capillary gas chromatography–mass spectrometry as part of a study to identify signature lipids for dinoflagellates in marine organic matter. Complex mixtures were found in each species with over 20 sterols identified in all. All species contained the same core group of sterols, but there were significant differences in the proportions of the various sterols. Two distinct groupings could be discerned in the sterol patterns. The 4-methyl sterol 4α,23,24-trimethyl-5α-cholest-22 E-en-3β-ol (dinosterol), which is common in many dinoflagellates, predominated in P. balticum and in P. minimum whereas in the closely related species P. micans and P. mexicanum the major sterol was cholesterol. A novel monounsaturated C 23 sterol having a much shortened side-chain was found in P. balticum and P. minimum and both P. balticum and P. minimum contained peridinosterol (4α,23,24-trimethyl-5α-cholest-17(20)-en-3β-ol). 24-Methylenecholesterol was only found in P. minimum, where it comprised over one-third of the sterols. The steroid ketone dinosterone occurred in P. balticum, but none of the other species contained steroid ketones. Although all the sterol distributions were broadly similar, the presence or absence of specific components might be a useful chemotaxonomic tool for distinguishing between closely related species.