Methods for the chemical synthesis of [23−3H2]lanosterol, [23,25−3H3]24-methyldihydrolanosterol and [24,28−3H2]24-methyldihydrolanosterol are described. It is shown that, in the biosynthesis of ergosterol from [26,27−14C2,23−3H2]lanosterol by the whole cells of Saccharomyces cerevisiae, one of the original C-23 hydrogen atoms is lost and the other is retained at C-23 of ergosterol. It is also shown that 24-methyldihydrolanosterol is converted into ergosterol in good yield and without prior conversion into a 24-methylene derivative. On the basis of these results possible pathways for the formation of the ergosterol side chain from a 24-methylene side chain are discussed.
