FREE AND COMBINED STEROLS OF PAVLOVA-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 4-alpha-methyl ergostanol, 4-alpha-methyl poriferastanol, and 4-alpha-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 of Pavlova but contain an extra nuclear hydroxyl which can be acetylated when present on a desmethyl sterol, but which is nonreactive with acetic anhydride in 4-alpha-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.