The introduction of the C-22–C-23 ethylenic linkage in ergosterol biosynthesis

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Abstract
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 orginal C-23 hydrogen atoms is lost and the other is retained at C-23 of ergosterol. It is also shown that 24-methyldidhydrolanosterol 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.