Free and combined sterols ofPavlova gyrans

Pavlova gyrans, a unicellular alga of interest as food for oysters, was cultured axenically and examined for sterol composition. Desmethyl monohydroxy sterols, which are frequently seen in algae, made up 40% of the total sterols and were observed primarily in the free sterol fraction. The principal sterols of this group were 5‐ergostenol, poriferasterol, and clionasterol, as well as some poriferast‐22‐enol and poriferastanol. Several “methyl” sterols with unusual structures made up 27% of the total sterols. The principal “methyl sterols” were 4α‐methyl ergostanol, 4α‐methyl poriferastanol, and 4α‐methyl poriferast‐22‐enol. Methyl sterols were found primarily in the ester fraction. Also observed was a new class of dihydroxysterols composing 33% of the total sterols. These sterols are structurally related to the methyl and desmethyl sterols ofPavlova but contain an extra nuclear hydroxyl which can be acetylated when present on a desmethyl sterol, but which is nonreactive with acetic anhydride in 4α‐methyl sterols. None of these sterols were observed in ester form but are concentrated in the acid‐hydrolyzable, bound fraction. The unique nature of these sterols suggests potential taxonomic utility.