The stereochemistry of hydrogen elimination in the biological conversion of 5α-cholest-8-en-3β-ol to 5α-cholest-7-en-3β-ol

The stereochemistry of 5α-cholest-8-en-3β-ol to 5α-cholest-7-en-3β-ol isomerization was studied in rat liver homogenates incubated in the presence of either 3(±)-2R-[2- 3 H 1 ]- or 3(±)-2S-[2- 3 H 1 ]-mevalonic acid lactone. The isolated radioactive 5α-cholest-7-en-3β-ol and cholesta-5,7-dien-3β-ol acetates were transformed into the mixtures of epimeric cis-5α-cholestane-3β,7,8-triol-3β-acetates and then into the mixtures of epimeric 5α-cholestane-3β,8-diol-7-one 3β-acetates. Radioactivity contents showed that during the biological isomerization the 7α-hydrogen of 5α-cholest-8-en-3β-ol is completely eliminated whereas the 7β-hydrogen is retained.