Preparation of 5alpha;-3beta;-2Hcholestan-3alpha;-ol by isomerization reactions

摘要

1438 J.C.S. Perkin IPreparation of 5a-3P-2H Cholestan-3a-ol by lsomerization ReactionsBy Josef E. Herz ldquo;t and Lilia A. MBrquez, Departamento de Quimica, Centro de lnvestigacion y de EstudiosAvanzados del lnstituto Politecnico Nacional, Apartado Postal 14-1 740, Mexico, D.F. MexicoJan Sjovall, Department of Chemistry, Karolinska Institutet, S-104 01 Stockholm, SwedenThe preparation of 5a- 3(3-2H cholestan-3a-ol by isomerization of the easily accessible 5a- 3a-2H cholestan-3P-01was investiaated. lsomerization of the mesvlate in collidine-water or treatment of the 3p-01 with benzoic acid inthe presence of triphenylphosphine and dietlsquo;hylfrom C-3.LABELLING of hydroxy-steroids with deuterium a t thehydroxylated carbon atoms is most easily achieved byreduction of the corresponding 0x0-steroids with sodiumborodeuteride or lithium aluminium deuteride.How-ever, this method cannot be used to obtain labelled 301-hydroxy-5a-steroids since these reductions give almostexclusively the equatorial 3p-is0mer.l The presentinvestigation was carried out to determine whetherepimerization reactions 2 9 3 could be used to prepare3a-hydroxy-5a- 3 (3-2H steroids of high isotopic purity.Four different experiments were performed, and theresults are summarized in the Table. Insignificant loss oft Present address: Department of Chemistry, KarolinskaInstitutet, S-104 01 Stockholm, Sweden.D. M. S . Wheeler and M. M. Wheeler, in lsquo; Organic Reactionsin Steroid Chemistry,rsquo; vol. 1, eds. J. Fried and J. A. Edwards,Van Nostrand Reinhold, New York, 1972, p.61.azodicarboxylate yielded the 3a-isomer with no loss of deuteriumdeuterium was observed during isomerization of thelabelled 3p-mesyloxy-steroid in collidine-water, yieldinga mixture of 5a-cholestan-3a-01 (50y0), 5a-cholest-2-ene (40y0), and small amounts of 5a-cholestan-3p-01.Similarly the reaction of the labelled 3p-hydroxy-steroidwith benzoic acid in the presence of triphenylphosphineand diethyl azodicarboxylate gave 5a-cholestan-3a-ylbenzoate in 90 yFld with little deuterium loss. Therewas no detectable incorporation of deuterium into an un-labelled steroid during isomerization in deuterium oxide.Little, if any, randomization of deuterium took placeduring inversion of configuration.L.F. Fieser and M. Fieser, in lsquo;Steroids,rsquo; Reinhold, NewYork, 1969, p. 324.a A. K. Bose, B. Lal, W. A. Hoffman, and M. S. Manhas,Tetvahedvon Letters, 1973, 1619 (see references to the originalmethod by Mitsunobi and Yamasaka in this paper)1974 1439These methods of inversion of readily available 3p-Iiydro~y-5a-~3a-~Hsteroids provide simple and practicalmeans of preparation of 3whydroxy-5ct- 3@-2Hsteroidswith high retention of label.EXPERIMENTALGas cllromatography-mass spectrometry (g.1.c.-n1.s.) wascarried out with an LKB 9000 instrument (column of 1.5SE-30 on Chroinosorb W HP). Multiple spectra wererecorded on magnetic tape and average isotope content wasAfter 24 h at room temperature, the solvent was removedunder vacuum. The residue, in ether, was washed severaltimes with aqueous 20 potassium hydroxide, water, anddilute acid, dried, and evaporated.The product was dis-solved in dry tetrahydrofuran, lithium aluminium hydride(10 mg) was added, and the mixture was refluxed for 1 11,acidified, diluted with ether, washed, and evaporated. Asample of the product was converted into the trimethylsilylether and was analysed by g.1.c.-m.s.Oxidation of the Isornerization Products.-To a solution ofFormation of deuteriated and unlabelled 5a-cholestan-3a-01 under various conditions of epimerization ofunlabelled and 3a-deuteriated 5a-cholestan-3p-01Deu.terium content and reaction conditionsr h 3 u-~H -3 p-013a-,H-3p-yl 3~.-~H-3P-yl 3 u-'H)- 3 p- yl +Ph,P + PhC0,H +Starting material mesylate + H,O mesylate + 2H20 mesylate + 2H,0 (KC0,Et)and products lH1 ,Hl IHl 2H1 lH1 ?H, lH1 ,Hl5x-Cholestan-3P-01 2.1 97.9 2.1 97.9 100 2.1 97.95r-Cholestan-3a-01 b 3.4 96.6 3.6 96.4 99.9 0.1 3.3 96.75a-Cholestan-3-one c 96.8 3-2 96.5 3.5 99.7 0.3 98-3 1.7a Starting material.Epimerization product. Formed by oxidation of epimerization product; converted into the O-methyl-oxime for estimation of 2H content.determined by comparisons with the unlabelled compoundusing ail IBM 1800 computer.*Isolnerimtion of 5a-3ce2H Cholestan-3P-yZ MesyZate.-Asolution of the mesylate (20 mg) in collidine (0-85 ml) andwater (0.15 ml) was refluxed for 24 h, poured on ice, andextracted with ether. The extract was washed with M-hydrochloric acid and water, dried, and evaporated.Thetrimethylsilyl ether, prepared in the usual way, was ana-lysed by g.1.c.-m.s. The sample was also analysed by t.1.c.on silica gel (chloroform as eluant). Authentic samples of5a-cholestan-3P- and -3a-01s and 5a-cholest-2-ene served asreference compounds.Isomerization of 5~-3a-~H Cholestan-3P-0Z.~-To a solu-tion of the steroid (10 mg), triphenylphosphine (14 mg) andbenzoic acid (6.3 mg) in dry tetrahydrofuran (0.5 ml)diethyl azodicarboxylate (4.2 mg) in tetrahydrofuran (0-3ml) was added with stirring and with exclusion of moisture.R. Reimendal and J. Sjovall, Analyt. Chem., 1972, 44, 21.ti J. L. Pinkus, G. Pinkus, and T. Cohen, J . Org. Chem., 1962,27, 4356.5~-3a-~Hcholestan-3P-o1 (15 mg) in dry methylene chloride(2 ml) was added chromium trioxide-pyridine complex(60 mg), and the mixture was stirred at room temperatureovernight. The solvent was evaporated off in a stream ofdry nitrogen and the residue was dissolved in dry pyridine( 1 ml). Methoxyamine hydrochloride (15 nig) was thenadded and the mixture was left for 24 h with exclusion ofmoisture. The solvent was evaporated off in a stream ofdry nitrogen and the residue was dissolved in ether. Thesolution was washed with water, dried (Na,SO,), and evap-orated.The technical assistance of Mrs. K. Robertsson is grate-This work was supported by grants fully acknowledged.from the Swedish Medical Research Council and W.H.O.4/054 Received, 14th January, 19741J. C. Collins, W. W. Hess, and I?. J. Frank, TetrahedronLetters, 1968, 3363