Biotransformation of 24 alpha-methylcholesterol and 24 beta-methylcholesterol by yeast mutant GL7

Incubation of 24 alpha- and 24 beta-methylcholesterols with yeast mutant GL7 afforded their corresponding C-22-desaturated products under the catalysis of sterol delta 22(23)-desaturase. The metabolites were identified to be 22-dehydro-24 alpha-methylcholesterol (2% yield from 24 alpha-methylcholesterol) and 22-dehydro-24 beta-methylcholesterol (51% yield from 24 beta-methylcholesterol) respectively on the basis of their chromatographic and spectral properties. It was concluded that the sterol delta 22(23)-desaturase prefers the 24 beta-methyl sterols and is highly stereospecific.