Dinosterol side chain biosynthesis in a marine dinoflagellate, Crypthecodinium cohnii

The heterotrophic dinofiagellate, Crypthecodinium cohnii, cultured in a nutrient medium containing methionine-[CD₃] incorporated deuterium into the newly synthesized 4α-monomethyl compound dinosterol (4α,23,24-trimethylcholest-22-en-3β-ol). The MS fragmentation pattern indicated that the C-23 methyl group contained three deuterium atoms and was introduced intact by transmethylation from methionine. The C-24 methyl group contained only two deuterium atoms which is consistent with the production of a 24-methylenesterol intermediate which is subsequently reduced to give the 24-methyl side chain. Mechanisms are proposed to account for the production of the dinosterol side chain.