The Stereochemistry of Tritium at Carbon Atoms 1, 7, and 15 in Cholesterol Derived from (3R,2R)-(2-3H)-Mevalonic Acid

Cholesterol was biosynthesized from (3R,2R)-(2-3H)(2-14C)-mevalonic acid. The cholesterol was degraded appropriately, and the presence and stereochemistry of three tritium atoms in the cholesterol nucleus were deduced. 5α-Cholestan-3-one, derived from the cholesterol, was dehydrogenated with dichlorodicyanobenzoquinone to 5α-cholest-1-en-3-one, a reaction involving loss of the 1α and 2β axial hydrogens, without loss of tritium. Oxidation of the 5α-cholest-1-en-3-one to 1,2-seco-A-norcholestan-1,2-dioic acid was accompanied by removal of tritium. Thus, it was concluded that tritium having the β configuration was present at C-1 in the cholesterol. The photolytic conversion of the cholesterol to 5α-hydroperoxycholest-6-en-3β-ol, which occurs with the stereospecific removal of the 7α hydrogen, proceeded without loss of tritium. Tritium was, however, lost when the hydroperoxide was converted to cholest-5-en-3β-ol-7-one. Hence, the presence of tritium at C-7 in the β configuration was inferred. The presence of α-oriented tritium at C-15 was indicated when progesterone, derived from the enzymatic side chain cleavage of the cholesterol, was converted microbiologically to pregn-4-en-12β,15α-diol-3,20-dione with loss of tritium. 15β-3H-Progesterone was synthesized and subjected to the same microorganism, giving the 12β,15α-diol, with retention of tritium, thereby indicating the validity of the approach. In addition to the three labels located at carbon atoms 1, 7, and 15, the presence of two further tritium atoms was indicated. It is assumed that these are located at carbon atoms 22 and 26. In summary, we have shown that during the transformation from lanosterol to cholesterol the 2-pro-R hydrogen of mevalonic acid at C-1 retains its β configuration, at C-7 is inverted from the α to the β orientation, and at C-15 is inverted from the β to the α configuration. It follows that the proton originating from the 2-pro-S hydrogen of mevalonic acid is lost at both carbon atoms 7 and 15.