Marine sterols. V. Isolation and structure of occelasterol, a new 27-norergostane-type sterol, from an annelida, Pseudopotamilla occelata

Occelasterol, a new marine C₂₇ sterol, has been isolated from an annelida, $\text{Pseudopotamilla occelata}$ and its structure was confirmed as 22-$\text{trans}$-27-nor-(24S)-24-methylcholesta-5, 22-dien-3β-ol (IIa) from the spectral data and by synthesis. Thissterol, the second member of a class of sterols having 27-norergostane-type side chain, had been formerly regarded as 22-$\text{cis}$-cholesta-5, 22-dien-3β-ol (Va). Gas-liquid Chromatographic studies have shown that occelasterol is distributed in various amounts in most of marine invertebrates.