Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
An Effective Procedure for the Synthesis of 1α,25-Dihydroxy-cholecalciferol (Calcitriol) Starting with 1α,3β, 25-Trihydroxy-cholesta-5,7-diene (Pro-Calcitriol)In order to develop an effective synthesis of the important vitamin D metabolite 1α,25-(OH)2-cholecalciferol (calcitriol) 5a starting with pro-calcitriol 1a the influence of reaction temperature and degree of turnover of 1a to the compositions of the photoproducts at irradiation in a 500 ml photoreactor were investigated. The combination of the highly photostable filter solution consisting of 2,7-dimethyl-3,6-diaza-cyclohepta-1,6-diene-tetrafluoroborate and biphenyl in ethanol realizes the double wavelength irradiation in the range of 290 to 300 nm and 〉 330 nm resulting in a highly amount of the desired pre-calcitriol 2a. The reversible photoisomers of pre-calcitriol 2a 1α,25-(OH)2-lumisterol3 4a and 1α,25-(OH)2-tachysterol3 3a were isolated from an irradiation mixture in pure form by means of an appropriate combination of flash-chromatography, MPLC and preparative HPLC, respectively. The isomers 2a, 3a and 4a were characterized chromatographically and spectroscopically. Photoisomerization of 1a at -45 °C using the filter solution mentioned above and recycling all reversible photoisomers resulted in highly pure 5a after thermally induced isomerization of 2a isolated from the irradiation mixture by means of flash-chromatography on Ag+- impregnated silica with a yield of 68%.
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