SHORT SIDE-CHAIN STEROLS FROM THE TUNICATE POLIZOA-OPUNTIA

The sterol composition of the Patagonian tunicate Polizoa opuntia was examined, and twenty-four compounds ,cere identified as having either a Delta(5), Delta(7), or Delta(0) nucleus. Two of them, the rare 20-me thylpregn-5-en-3 beta-ol and 20-ethylpregn-5-en-3 beta-ol, were previo usly unreported as natural products from tunicates. These compounds we re present only as trace components; therefore, their structures were confirmed by synthesis from suitnble precursors and by comparison of t he spectral and chromatographic constants of the synthetic and natural compounds.