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A new route for the preparation of the 22,23-dioxocholestane side chain from diosgenin and its application to the stereocontrolled construction of the 22R,23S-diol function
Authors:Susana Rincón  Jesús Sandoval-Ramírez  Ma Antonieta Fernández  Rosa Santillan
Institution:a Departamento de Química, Centro de Investigación y de Estudios Avanzados del IPN, Apdo. Postal 14-740, 07000 México D.F., México
b Instituto de Investigaciones Químico Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Ciudad Universitaria, 58030 Morelia, Mich., México
c Facultad de Ciencias Químicas, Benemérita Universidad Nacional Autónoma de Puebla, Ciudad Universitaria, Col. San Manuel, C.P. 72570, Puebla, Pue., México
d Departamento de Química Orgánica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México, D.F., México
Abstract:The new (22R,23S,25R)-3β,16β,26-triacetoxy-cholest-5-ene-22,23-diol (11a) was synthesized from diosgenin (3) through a synthetic route based on chemoselective RuO4 oxidation of (25R)-3β,16β-diacetoxy-23-ethyl-231,26-epoxycholesta-5,23(231)-dien-22-one (9) that afforded (20S,25R)-3β,16β,26-triacetoxycholest-5-ene-22,23-dione (10) which was stereoselectively reduced using NaBH4. Compound 9 was obtained from the known isomeric 22,26-epoxycholest-5-ene steroidal skeleton 8b by treatment with p-TsOH in toluene, amberlyst-15 or directly from diosgenin by treatment with BF3·OEt2/Ac2O. Chemoselective reduction of the 23-keto group of 10, was attained using NaBH4/ZnCl2 at −70 °C to give 23S-14. The NMR spectra of all compounds were unambiguously assigned based on one and two dimensional experiments and the C-22 and C-23 stereochemistry in the diacetate derivative 11b, as well as the structure of epoxycholestene 9 were further established by X-ray diffraction analyses. The new route for the functionalization of the side chain of diosgenin can find application in the synthesis of norbrassinosteroid analogues.
Keywords:Diosgenin  22  23-Dioxocholestene  22  23-Cholestanediol  NMR
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