The stereochemistry of hydrogen elimination from C-7 in cholesterol and ergosterol biosynthesis

[摘要]

The synthesis of [7α-³H]lanosterol is described. It is shown that in the conversion of [7α-³H,26,27-¹⁴C₂]lanosterol into cholesterol by a rat liver system, it is the 7β-hydrogen atom that is predominantly removed. On the other hand, the conversion of doubly labelled lanosterol into ergosterol by whole yeast cells results in the loss of the 7α-hydrogen atom. These results therefore suggest that the C-7 hydrogen atoms with opposite stereochemistry are labilized by the rat liver and the yeast Δ⁸–Δ⁷ steroid isomerases.