Biosynthetic Studies of Marine Lipids. 4. Mechanism of Side Chain Alkylation in (E)-24-Propylidenecholesterol by a Chrysophyte Alga

Article abstract of DOI:10.1021/jo00194a014

A photosynthetic marine Chrysophyte (unicellular alga) was cultured in a medium containing labeled methionine (methyl-¹³C, methyl-d₃).The ²H and ¹³C distribution in the alkyl substituents of the sterols was determined by ²H and ¹³C NMR.Although two novel cyclopropyl sterols - (24R,28R)- and (24S,28R)-24,28-methylene-5-stigmasten-3β-ol - and their ring opening products were found as trace sterols in the alga, the results of ²H NMR indicate that the substituent in the side chain of the main sterol ((E)-24-propylidenecholesterol) is not formed by ring opening of these cyclopropyl sterols.Instead, the main sterol is most likely formed by further alkylation of a 24-vinyl sterol which has so far not been been encountered in nature.Other novel sterols encountered in the Chrysophyte belong to the rare classes of Δ²³, 14α-methyl, and Δ^8(14),15-diene sterols.