Recent studies have led to the identification of an unusual class of dihydroxysterols (steroidal diols termed 'pavlovols') in a few species of microalgae from the genus Pavlova (family Pavlovaceae, class Haptophyceae = Prymnesiophyceae). These compounds have an additional hydroxyl group at C-4 in the sterol A ring, which appears to be very rare in sterol biosynthetic pathways. The sterol compositions of many other haptophytes from different orders have been analyzed, but to date all have lacked pavlovols. We now report the occurrence of these compounds in Diacronema vlkianum Prauser and two strains of Pavlova pinguis Green. This is the first report of the lipid composition of these species. Both microalgae contained '24-methylpavlovol' (4α, 24-dimethyl-5α-cholestan-3β,4β-diol), P. pinguis also contained '24-ethylpavlovol' (4α-methyl-24-ethyl-5α-cholestan-3β,4β-diol), and D. vlkianum contained a diol identified from its mass spectrum as 4α,24β-dimethyl-5α-cholest-22E-en-3β,4β-diol. Both species contained structurally analogous 4-desmethyl sterols and 4-methyl sterols, although there were major differences in the proportions in each series. The major 4-desmethyl sterol in both species was 24-ethylcholesta-5,22E-dien-3β-ol and the major 4-methyl sterol was 4α-methyl-24-ethyl-5α-cholest-22E-en-3β-ol. The presence of pavlovols in P. pinguis, combined with earlier data, suggests that all Pavlova species might have this distinguishing lipid feature. However, their identification in D. vlkianum extends the occurrence of these compounds to another genus and shows that they are not unique to the genus Pavlova. However, they are probably restricted to species from the order Pavlovales. The modes of biosynthesis and functions of pavlovols remain unknown.
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Plant Science
- Fatty acids
- Steroidal diols