[24,25-³H]cholesterol: Presence of tritium at additional sites in the side chain

In order to measure the distribution of radioactivity present in the side chain of [24,25-³H]cholesterol prepared by a sequence involving catalytic tritiation of 3α,5α-cyclocholest-24-en-6β-ol 6-methyl ether, the cholesterol was oxidized to 4-cholesten-3-one, which was then cleaved between C-24 and C-25 to afford the C₂₄ alcohol. Oxidation to the corresponding cholenoic acid, followed by alkali equilibration and esterification completed the sequence. It was found that about 20% of the tritium in the labeled cholesterol is not lost when this tracer is physiologically converted to bile acids. Consequently, measurements of bile acid formation using this tracer must be corrected upward by this amount.