Zusamnenfassung. 25-Hydroxycholestcrin (4) ist in 30proz. husbcute in sieben Schritten aus Stigmastcrin (6) hergestellt wordcn. Dcr wichtigste Schritt ist die Umsetzung des Tosylats 11 mit Clem hcctylenderivat 13 zu 14 unter Bildung d r s vollstandigen Cholesteringeriists. Significant breakthroughs have been made with respect to the structures and the modes of action of the biologically active forms of vitamin D, (1) [I]. 25-Hydroxycholecalciferol (2) [2] and 1 M , 25-dihydroxycliolecalciferol (3) [3], the major metabolites of cliolecalciferol (l), are inore potent than l in allthree criteriaof physiological activity, namely, increased calcium transport, bone mineral mobilization, and calcification [I]. Since hydroxylation occurs first in the liver (25-OH) and then in the kidney (3 cr.-OH) before the onset of activity [I], cholecalciferol (1) should be viewed 4 K -H 5 R = 01%

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the rate constants of the exchange at various temperatures, using the INVERS EXII program1* and the parameters as above. The Arrhenius plot yielded the activation energy of 14.1 f 0.6 kcal/mol. Then the enthalpy, entropy, and free energy of activation a t 25" were obtained as 13.5 * 0.6 kcal/mol, 9.8 i 3.0 eu, and 10.6 f 1 .O kcal/mol, respectively. l 3 T o the best of our knowledge, this is the first example of observing the nonequivalence of the methyl protons in high resolution nmr spectroscopy. l 4

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