Preparation of tritium‐labeled sterols and the synthesis of labeled‐24‐azacholesterol

A method is presented for the preparation of 2,4‐3H‐sterols (stigmasterol, β‐sitosterol, campesterol, fucosterol and 7‐dehydrocholesterol) via the technique of exchange‐labeling of keto steroids and their subsequent conversion to sterols. The preparation of tritium‐labeled 3β‐hydroxy‐24‐norchol‐5‐en‐23‐oic acid and the synthesis of 2,4‐3H‐24‐azacholesterol are reported. Some advantages of the exchange‐labeling method over the conventional catalytic exchange method are discussed.