Reduction of the 24,25-double bond of lanosterol in vivo in the rat. Stereochemistry of the addition of the C-25 proton in the biosynthesis of cholesterol

The stereochemistry of addition of the 25-proton in the Δ²⁴ reduction of lanosterol to cholesterol in vivo in the rat is shown to be the same as that in the S-10 fraction of rat liver homogenstes. It is also shown that oxidation of [1,2-³H₂]octan-1-ol by the Pfitzner-Moffatt method proceeds with complete removal of tritium from C-2 of octanol. A similar oxidation of [25-³H]-5α-cholestane-3β,26-diol to 3-oxo[25-³H]-5α-cholestan-26-al resulted in the loss of 23% of tritium. In contrast, Collins oxidation of [1,2-³H₂]octan-1-ol to octanal did not involve any loss of tritium from C-2.