Stereochemical Features of C-methylations on the Path to Δ24(28)-Methylene and Δ24(28)-Ethylidene Sterols: Studies on the Recombinant Phytosterol Methyl Transferase from Arabidopsis thaliana

Using a homogenate prepared from Escherichia coli cells that express the sterol methyl transferase (SMT) gene of Arabidopsis thaliana , migration of the hydrogen atom at C-24 to C-25 from the Re -face of the double bond was demonstrated in the biosynthesis of [27- 13 C] 24(28)-methylenezymosterol (fecosterol) from [27- 13 C]zymosterol and the chirality of the C-25 stereocenter (25 R ) was found to be retained after the stereospecific conversion of [27- 13 C]24(28)-methylenezymosterol to [27- 13 C](24(28) Z ) -ethylidenecholest-8-en-3β-ol. © 1997 Elsevier Science Ltd.