Investigations on the biosynthesis of steroids and terpenoids. Part II. Role of 24-methylene derivatives in the biosynthesis of steroids and terpenoids

Abstract

24,25-Dihydro-24-methylenelanosterol has been synthesised from lanosterol and investigated as a potential precursor of eburicoic acid and of ergosterol.

Two new sterols, 24,25-dihydro-4α-methyl-24-methylenezymosterol and 3β-hydroxy-4α-methylcholesta-8(14),24-diene have been isolated from yeast residues and their structures have been determined. The constitution of 24,25-dihydro-4α-methyl-24-methylenezymosterol has been confirmed by a partial synthesis from the more abundant 4α-methylzymosterol.

4α-Methylzymosterol, 24,25-dihydro-4α-methyl-24-methylenezymosterol and obtusifoliol have been shown to be incorporated into ergosterol in yeast cultures. 4,4-Dimethylergosterol is, however, not a precursor.

By a trapping experiment in which tritium-labelled squalene oxide and unlabelled 24,25-dihydro-24-methylene-lanosterol were used it has been shown that the latter is almost certainly not on the biogenetically preferred route from lanosterol to ergosterol.