Isolation of sterols with cyclopropyl-containing side chains from the cultured marine alga peridiniumfoliaceum

The sterol fraction of the cultured dinoflagellate $\text{Peridinium}$$\text{foliaceum}$ contains in addition to cholesterol, 24-methylcholesterol, 4,24-dimethylcholesterol and dinosterol ($\text{3c}$) small amounts of the cyclopropyl-containing sterols gorgosterol ($\text{1a}$) and 5α-gorgostanol ($\text{1b}$) as well as 4α-methylgorgostanol ($\text{1c}$) and E-4α,22ξ,23ξ (or 24ξ)-trimethylcholest-17(20)-en-3β-ol ($\text{6c}$ or $\text{7c}$). The biosynthetic implications of the first isolation of such sterols from a free-living alga are emphasized.