14 Biological Chemistry Part (ii) Steroids By D. N. KIRK Chemistry Department Westfield College Hampstead London NW3 7ST 1 Introduction This Report presents a selection of the work published during 1974 and 1975. The fourth and fifth annual volumes of the Chemical Society’s Specialist Periodical Report on Terpenoids and Steroids have appeared with comprehensive coverage of the literature from September 1972 to August 1973 and the corresponding period in 1973-1974 respectively. Sections on ‘Steroid Properties and Reactions’ appear in both volumes. ‘Microbiological Reactions with Steroids’ and ‘Steroid Conforma- tions from X-Ray Analysis Data’ are reviewed in Volume 4 and ‘Steroid Synthesis’ in Volume 5. The sixth volume of the series is expected during 1976.2 Synthetic Transformations The discovery that ‘vitamin D’ is transformed in vivo into its la,25-dihydroxy- derivative (l) the active form of the vitamin has prompted intensive studies in synthesis. The 1a-hydroxy-group has been introduced by reactions of suitable 1a,2a-epoxy-derivatives with lithium-ammonia’*2 or aluminium amalgam,3 or by selective hydroboration of a 1’5-dien-3 p-01.~The 5,7-diene system required for photoisomerization to the ‘previtamin’ [9( lO)-seco-5( 10),6,8-triene (2)] has been HO‘ (1) D. H. R. Barton R. H. Hew M. M. Pechet and E. Rizzardo J.C.S. Chem. Comm. 1974,203. D. Freeman A Acher and Y. Mazur TetrahedronLetters 1975,261. 3 T. A. Narwid J. F. Blount J. A. Iacobelli and M. R. Uskokovic Helu. aim. Acta 1974,57,781.C. Kaneko S. Yamada A. Sugimoto Y. Eguchi M. Ishikawa T. Suda M. Suzuki S. Kakuta and S. Sasaki Steroids 1974,23 75. 366 Biological Chemistry -Part (ii) Steroids introduced either before5 or after4 the 1a-hydroxylation sequence (Scheme 1). Protection of the sensitive 5,7-diene was achieved by formation and subsequent reductive cleavage of the adducf with 4-phenyl-1,2,4-triazoline-3,5-dione. \ 0 HO viii xii i iiJ 1 7 0hi Reagents i K0Bu'-DMSO; ii H+ (kinetic control); iii NaBH,; iv B,H, H,O,-HO-; v H,O,-HO-; vi Li-NH,-NH,Cl; vii Al-Hg NaBH, LizC03-DMF; viii Ca(BH,) ;ix 4-phenyl-1,2,4- triazoline-3,5-dione;x m-CIC6H4C03H;xi LiAIH4 ;xii dibromodimethylhydantoln,(MeO)JP. Scheme 1 The 25-hydroxycholestane side-chain is usually obtained by Grignard methylation of a 27-norcholestan-25-one which was originally obtained as a by-product of cholesterol oxidation.The 25-ketone is now available by novel routes from either an androstan- 17-one6 or a pregnan-20-one.' An alternative synthesis of 25-hydroxycholesterol employs a Gzintermediate (3) obtained from stigmasterol the rest of the side-chain being added by use of the lithium acetylide derivative (4).* Some vitamin D derivatives with additional hydroxylation at C-24 have also been synthesized.' Androstane" and pregnane'' analogues of 1a-hydroxy-vitamin D are almost devoid of biological activity. C. Kaneko A. Sugimoto Y.Eguchi S.Yamada M. Ishikawa S. Sasaki and T. Suda Tetrahedron 1974 30,2701. J. Wicha and K. Bal J.C.S.Chem. Comm. 1975,968. T. A. Narwid K. E. Cuoney and M. R. UskokoviE Helv. Chim. Acra 1974,57,771. 8 J. J. Partridge S.Faber and M. R UskokoviE Helv. Chim. Ada 1974,57,764. N. Ikekawa M. Morisaki N. Koizumi Y.Kato and T. Takeshita Chem.and Phrm. Bull. (Jupan),1975 23,695; M. Seki N. Koizumi M. Morisaki and N. Ikekawa TerrahedronLetters 1975,15; N. Koizumi M. Morisaki N. Ikekawa A. Suzuki and T.Takeshita ibid. p. 2203; N. Ikekawa M. Morisaki N. Koizumi M.'Sawamura Y.Tanaka and H. F. DeLuca Biochem.Biophys. Res. Comm. 1975,62,485. lo H. Sakamoto A. Sugimoto C. Kaneko T.Suda and S. Sasaki Chem. and Pharm. Bull. (Japan),1975 23 1733. H.-Y. Lam H.K.Schnoes I-l. F. DeLuca and L. Reeve Steroids 1975,26,422. 368 D.N. Kirk (5) OMe (3) The first satisfactory syntheses are reported for 18’2 l-dihydroxypregn-4-ene- 3,20-dione [‘18-hydroxy-deoxycorticosterone’; as hemiacetal (6)] a steroid impli- cated in hypertension.The 18-hydroxy function was introduced into a pregnan-20- one via the 2Op-01 either by the ‘hypoiodite’ sequence” or by photolysis of the 20-nitrite in the presence of oxygen,13 which affords the 18-nitrate. 18-Hydroxypregn-4-ene-3,20-dione(in 18-+20-hemiacetal form (7)] gives the 21- acetoxy-derivative (8) in a single step by reaction with lead tetra-acetate.” The intermediate 18,20-epoxypregn-20-ene (9) can be obtained if required by treating (6) R = OH (7)R = H (8) R = OAC the hemiacetal(6) with aluminium isopropoxide in toluene,14 but is very sensitive to acids. A new synthesis of compounds of the aldosterone series proceeds via the Barton reaction (photolysis of an 11p-nitrite) to the 18-oxhe and thence the nitrone (10).15 Choice of the 1,4-dien-3-one as the starting material prevented competing attack on the C-19 methyl group.Either labelled or unlabelled aldosterone could be produced in a final selective hydrogenation of the 1,2-ethylenic bond. The nitrone function in compounds of type (10) provides the necessary activation for acetoxyla- tion at C-21 through acetylation and rearrangement leading to the 18,21-diacetate (1 1). Oxidation of the nitrone with Jones’ reagent can be controlled to give either the hemiacetal (12) or the lactone (13).15 New five-step carbonyl transpositions (Scheme 2) convert an androstan-17-one efficiently into the 16-0~0-i~0mer,’~ and enones into isomeric enones [e.g.3-oxo-A4 +4-0x0-A’ (Scheme 2) or 3-0x0-Ah’ -+2-0xo-A~I.’~ Beckmann cleavage and l2 D. N. Kirk and M. S. Rajagopalan J.C.S. Chem. Comm. 1974 145; J.C.S. Perkin I 1975 1860. I3 D. H. R. Barton M. J. Day R. H. Hesse and M. M. Pechet J.C.S. Perkin I 1975 2252. l4 M. Biollaz J. Kalvoda and J. Schmidlin Helo. Chim. Acta 1975,58 1425. D.H. R. Barton N. K. Basu M. J. Day R. H. Hesse M. M. Pechet and A. N. Starratt J.C.S. Perkin I 1975,2243. l6 B. M. Trost K. Hiroi and S. Kurozumi J. Amer. Chem. Soc. 1975,97,438. 17 M. K. Patel and W. Reusch Synth. Comm. 1975 5 27. Biological Chemistry -Part (ii) Steroids 0-R' 0'&ocH2R2 0& (11) R' = H OAC; R2 = OAC (12) R' = H OH; R2 = H (13) R' = 0;R2 = H Reagents i Li N-cyclohexyl-N-isopropylamide, THF -78 "C;ii PhSSPh HMPA 0°C;iii NaBH,-MeOH; iv MeSO,CI-py; v K0Bu'-DMSO; vi HgCI, MeCN-H,O; vii H,O,-NaOH ; viii MeONa-MeOH ; ix TsNHNH ; x 2MeLi ; xi H + Scheme 2 re-cyclization (Scheme 3) provides a route from a 17-0x0-steroid to its 18-nor analogue.18 New methods for building up steroid side-chains include reactions of 17-0x0-groups with tosylmethyl isocyanide l9 the a-1ithio-derivatives of ethyl diazoacetate lnM.M. Coombs and C. W. Vose J.C.S. Chem. Comm. 1974,602. l9 J. R. Bull and A. Tuinrnan Tetrahedron 1975 31 2151; J. R. Bull .I.Floor and A. Tuinrnan ibid.,p. 2157. 370 D.N.Kirk 1iii Reagents :i Dicyclohexylcarbodi-imide,CF,CO,H DMSO ;ii m-CIC,H,CO,H ;iii BF ,hydrolysis.Scheme 3 or isocyanoacetate,20 propen-2-yl-lithi~m,~' or tri-n-butyl(1-methoxycarbonyl-prop-2-ylidene)pho~phorane~~ (Scheme 4). A novel side-chain degradation Reagents i TsCH,NC; ii MeLi; iii CNCHC0,Et Li' ; iv CH,=CMe Li'; v PhSCI; vi Li+ NEt; ; vii PhSSPh; viii HgCl ;ix Bu,P=CMeCH,CO,Me Scheme 4 2o U. Schollkopf B. BBnhidai H. Frasnelli R. Meyer and H. Beckhaus Annalen 1974 1767. B. M. Trost and J. L. Stanton J. Amer. Chem. Soc. 1975,97,4018. 22 A. Scettri E. Castagnino and G. Piancatelli Gazzerta 1974 104,437. Biological Chemistry -Part (ii) Steroids 371 involves oxygenation of tne phenyl ketone (14) in alkaline solution the resulting bisnorcholan-22-oic acid (15) was further degraded by lead tetra-acetate in benzene-pyridine to the 20-acetoxypregnane (16).23 3 Oxidation and Reduction A new variation on the principle of 'remote oxidation' employs an iodo-aryl- substituted 3a-ester (see p.372) of 5tr -cholestan-3a-01.~~ Photolysis of the derived iododichloride (17) results in radical-induced chlorination at whichever tertiary centre is best placed for attack by the free radical generated at the iododichloride site (14a when the p-iodophenyiacetate is used or 9a with the rn -iodobenzoate). Alternatively iodobenzene dichloride may be photolysed in the presence of the steroid iodo-aryl ester which acts as a radical carrier with similar results.2s Dehydrochlorination of the 14a-or 9a-chlorinated steroids gave A14-or A9(")-enes respectively.9a -Chlorination of a suitable pregnane derivative by this method opened the way to a novel synthesis of A variant using the 3a-(4'- iodobiphenyl-3-carboxylate(18) permits attack at C- 17 leading to a procedure for removal of the entire side-chain and generation of a 17-0xo-group.~~ 1' (17) (18) The Oxford group continue to publish details of their studies on microbiological hydroxylation of varied steroid Lewis acids catalyse the oxygenation of ergosteryl acetate to give the 5a,8a-epidioxide oxygenation in the dark appears to involve triplet oxygen.28 Cholesteryl acetate can be nitrated safely at C-6 by using 23 M. Feiizon F. J. Kakis and V. Ignatiadou-Ragoussis Tetrahedon 1974,30 3981. 24 R. Breslow R. Corcoran J. A. Dale S. Liu and P.Kalicky J. Amer. Chem. SOC.,1974?-96 1973. 25a R. Breslow R. J. Corcoran and B. B. Snider 1 Amer. Chem. Soc. 1974,% 6791. 25b R. Breslow B. B. Snider and R. J. Corcoran J. Amer. Chem. SOC.,1974,96,6792. 26 B. B. Snider R. J. Corcoran and R. Breslow J. Amer. Chem. Soc. 1975,97 6580. 27 Sir E. R. H. Jones G. D. Meakins J. 0. Miners and A. L. Wilkins J.C.S. Perkin I 1975 2308 and references therein. 28 D. H. R. Barton R. K. Haynes P.D. Magnus and I. D. Menzies J.C.S. Chem. Comm. 1974,511;D. H. R. Batton R. K. Haynes G. Leclerc P. D. Magnus and I. D. Menzies J.C.S. Perkin I 1975,2055. 372 D.N.Kirk modified reaction condition~.~~ Iodine-potassium iodate in acetic acid3’ is a cheap and effective alternative to iodine-silver acetate for the conversion of 5a-cholest-2- ene into 2~-acetoxy-3a-iodo-5a-cholestane (Prevost reaction).The 2-ene with phenylselenenyl acetate unfortunately gives a mixture of the 2P-acetoxy-3a- phenylseleno- and the 3a -acetoxy-2~-phenylseleno-derivatives, leading to a mix- ture of two allylic acetates after oxidative elimination of selenium.31 Reduction [LiAlH(OBu‘),] of a series of 5a-cholestan-3-ones with C-5 sub- stituents gave product mixtures which are considered to imply dissymmetry of the carbonyl *IT* orbital depending upon the nature of the 5a-s~bstituent.~~ Sodium cyanoborohydride in acidified THF reduces 3-0x0-steroids selectively in the pres- ence of 17-0x0- or 20-0xo-functions.~~ 5a-Cholestan-3P-01 is among alcohols deoxygenated in useful yield by treating the thiobenzoate with trib~tylstannane.~~ 4 Substitution and Elimination Sa-Cholestan-3a-yl esters [e.g.(18)] required for ‘rtmote oxidations’ (see above) are available in a single step from the 3P-01 by the ‘substitution-inversion’ proce- dure using diethyl azodicarboxylate triphenylphosphine and the appropriate car- boxylic acid.26 3a-Phenoxy-derivatives result when a phenol is used in place of the carboxylic acid.35 Cholesterol with benzoic acid under these conditions gave a complex mixture including 3a,5a-cyclocholestanyl derivative^.^^ Potassium superoxide (KO,) with 18-crown-6 to capture potassium ions converted cholesteryl tosylate directly into cholest-5-en-3a-01 in an unusual direct substitution with inversion.37 Fluoro-derivatives are obtained from steroidal or their trimethylsilyl by the use of phenyltetrafluorophosphorane.Acetate ion converts a 4P-bromo-3-oxo-5P -steroid initially into the 20 -acet~xyketone,~’ which subsequently inverts to the more stable 2P-isomer. The implied mechanism (Scheme 5) includes allylic substitution by attack on the A2-enol with a trans relationship of the entering and leaving groups which is contrary to earlier evidence in favour of cis stereochemistry in comparable reactions but which may be compati- ble with recent orbital-symmetry consideration^.^^ Unexpectedly large effects of remote polar substituents (at C-17) on the rates of solvolysis of 5a-androstan-3-yl tosylates suggest that charge-dipole interactions between the reaction site and the substituent are modified by delocalization of negative charge into the 29 A.T. Rowland Steroids 1975 26 251. 30 L. Mangoni M. Adinolfi G. Barone and M. Parrilli Guzzeitu 1975,105,377. 31 K. B. Sharpless and R. F. Lauer J. Org. Chem. 1974 39 429. 32 C. Agarni A. Kazakos and J. Levisalles Tetrahedron Letters 1975 2035. 33 M.-H. Boutigue and R. Jacquesy Compt. rend. 1973 276 C 437. 34 D. H. R. Barton and S. W. McCornbie J.C.S. Perkin I 1975 1574. 35 M. S. Manhas W. H. Hoffman B. Lal and A. K. Bose J.C.S. Perkin I 1975,461. 36 R. Aneja A. P. Davies and J. A. Knaggs Tetrahedron Letters 1975 1033. 37 E. J. Corey K. C. Nicolaou M. Shibasaki Y. Machida and C. S. Shiner Tetruhedronhtters,1975,3183. 38 Y. Kobayashi I. Kumadaki A. Ohsawa M. Honda and Y. Hanzawa Chem.undPharm. Bull. (Jupun) 1975,23 196. 39 N. E. Boutin D. U. Robert and A. R. Cambon Bull. Soc. chim. France 1974 2861. 40 T. T. Takahashi and J. Y. Satoh Bull. Chem. Soc. Japan 1975,48,69. 41 R. L. Yates N. D. Epiotis and F. Bernardi J. Amer. Chem. SOC.,1975,97 6615. 42 P. E. Peterson and D. M. Chevli J. Org. Chem. 1974 39 3684. Biological Chemistry -Part (ii) Steroids -* ACO HO HO 0@-Br H 1 Scheme 5 5 Molecular Rearrangements The hyperacidic solvent system HF-SbF induces some remarkable carbocation rearrangements involving the steroid ‘backbone’. Oestr-4-ene-3,17-dione (19) is isomerized to the more stable 14p configuration (20) through migration of a cationic centre from C-5 to C-14 and back to C-5;43the carbocation can be intercepted mainly at C-8 by an added cycloalkane as reducing agent to give 5ar,8a,14@- and Sa,8p,14P-oestrane-3,17-diones(21).Gaseous hydrogen gives an alternative H0 0’ (19) 14a-H (20) 14p-H reduction product the rearranged ‘anthra-steroidal’ dione Oestrone (23) similarly affords the ‘anthrasteroid’ (22),44 although in the absence of a reducing agent oestrone and some of its isomers afford the de-aromatized oestra-4,9-diene- 3,ll-diones (24).45 The trienone (25) aromatizes in ring A as well as being 43 J.-C. Jacquesy R. Jacquesy and G. Joly Tetrahedron Letters 1974,4433;Bull. SOC. chim. France 1975 2281,2289. * 44 J.-c. Jacquesy R. Jacquesy and G. Joly Tetrahedron 1975,31 2237. 45 J.-P. Gesson J.-C. Jacquesy R. Jacquesy and G.Joly Bull. SOC.chim. France 1975 1179. 374 D.N. Kirk epimerized at C- 14 to give the phenolic product (26).46 Pregnan-20-ones isomerize in hyperacidic media to give a mixture of the four isomers resulting from equilibra- tion of configurations at C-13 and C-17 through a 13,17-~eco-intermediate.~' 'Backbone' rearrangements [e.g. (27) +(28)] induced by sulphuric acid-acetic anhydride apparently proceed through a concerted mechanism,48 for no isotope (27) (28) incorporation occurred in deuterium-labelled solvents. The amine holamine (29) and related compounds however rearrange (in H2S04)to give the 13(17)-ene (30) with extensive loss of a deuterium label from C-8,49implying that this reaction involves a deprotonation-reprotonation mechanism via an olefinic intermediate.Backbone isomerizations of androst-5-ene (31) and ~-homoandrost-5-ene (32) give A8-olefins (33) with equilibrated configurations at C-5 C-10 C-14 and (in the D-homo-compound) also at C-13; trifluoroacetic acid promotes these and related rearrangements under very mild c~nditions.~'The ease of rearrangement even in the D-homo-compound (32) contradicts the earlier view that strain at the trans-C/D 46 J.-C. Jacquesy R. Jacquesy and Ung Hong Ly Tetrahedron Letters 1974,2199. 47 J.-C. Jacquesy R. Jacquesy and J.-F. Patoiseau Bull. SOC. chim. France 1974 1959. 48 E. T.J. Bathurst and J. M. Coxon,J.C.S. Chem. Comm. 1974,131; E. T. J. Bathurst J. M. Coxon and M. P. Hartshorn Austral. J. Chem. 1974,27 1505. 49 J.Thierry F. Frappier M. Pais and F.-X. Jarreau Tetrahedron Letters 1974 2149. 5O D. N. Kirk and P. M. Shaw J.C.S. Perkin I 1975,2284. 375 Biological Chemistry -Part (ii) Steroids & 8 H H2In 10 \ l4H H2)n 5 \ Me (31) n = 1 (32) n = 2 (33) ring junction provided the ‘driving force’ for backbone rearrangements which are now seen as merely olefin equilibrations via cationic intermediates. The rearrange- ment of androst-5-en-17-one (34) stops at the intermediate 5-methyl-5P-oestr- 9(11)-en-17-one (35) in trifluoroacetic acid but proceeds further to give the two 8-enes (36) in sulphuric acid-methanol. (34) (35) (36) 5,104s Hydrogen fluoride induces extensive rearrangements in suitable cholestanes [e.g. (37) +(38)J; both the ‘backbone’ and the side-chain are in~olved.’~ HO.-9% HH HO..H OH (37) (38) The 9a,l la!-epoxide (39) was rearranged by boron trifluoride with lop-methyl migration to give in part the 9P-methyl product (40).52 AcO AcO (39) (40) 51 A. Ambles C. Berrier and R.Jacquesy Bull. SOC.chim. France 1975,835. 52 A. C. Campbell C. L. Hewett M. S. Maidbent and G. F. Woods J.C.S. Perkin I 1974 1799. 376 D.N. Kirk 6 Miscellaneous Reactions Prolonged heating in acetic anhydride-pyridine converts ketoximes into enimides through a radical mechanism. 5a -Cholestan-3-one oxime (41) gave the enimide (42) which afforded the enamide (43) after chromatography on alumina. When treated with lead tetra-acetate7 the enamide gave the a-acetoxy-ketone (44).53 (42) R = AC (43) R = H The oxime (45) of a 17-0x0-steroid gave the enamide (46) with the 13a-configuration; this efficient method of inversion of configuration at C-13 appears to be preferable to the earlier photoisomerization of a 17-0x0-steroid but like the (45) (46) latter is thought to proceed by a radical mechanism through a 13,17-seco-intermediate.54 A 20-oximinopregnane (47) was converted by an ingenious ‘one- pot’ application of the enamide-lead tetra-acetate sequence into the 17a,21- diace toxypregnan-20-one (48).55 Me CH,OAc I (47) (48) Tosylhydrazones afford the parent ketones on reaction with N-bromosuccinimide followed by sodium hydrogen s~lphite,~~ Diethylene or with titanium tri~hloride.~’ orthocarbonate converts ketones into ethylene acetals under very mild acidic 53 R.B. Boar J. F. McGhie M. Robinson D. H. R. Barton D. C. Horwell and R. V. Stick J.C.S.Perkin I 1975,1237. 54 R. B. Boar F. K. Jetuah J. F. McGhie M. S. Robinson and D. H. R. Barton J.C.S. Chem. Comm. 1975 748. 55 R. B. Boar J. F. McGhie M. Robinson and D. H. R. Barton J.C.S. Perkin I 1975 1242. 56 G. Rosini J. Org. Chem. 1974,39,3504. 57 B. P. Chandrasekhar S. V. Sunthankar and S. G. Telang Chem. and Ind. 1975,87. Biological Chemistry -Part (ii) Steroids conditions;'$ methyl thio trime t h ylsilane affords bis(me t h yl t hio)ace tals even without acid catalysis and attacks 5cu-androstane-3,17-dioneselectively at C-3.59 Glycoside formation from steroids,60 and the controlled trimethylsilylation of steroidal alcohols and enolizable ketones,61 have been reviewed.The absolute configurations of steroidal alcohols a-glycols and vicinal amino-alcohols can be determined by c.d. measurements on metal complexes.62 Steroidal ketones provided the majority of compounds used in a new and wide-ranging empirical analysis of c.d. data (n+ =*) for decalone ana10gues.~~ 58 D. H. R. Barton C. C. Dawes and P. D. Magnus J.C.S.Chem. Comm. 1975,432. 59 D. A. Evans K. G. Grimm and L. K. Truesdale J. Amer. Chem. Soc. 1975,97,3229. 6o G. Wulff and G. Rohle Angew. Chem. Internat. Edn. 1974 13 157. 61 H. Gleispach J. Chromatog. 1974,91,407. 6* J. Dillon and K. Nakanishi J. Amer. Chem. Soc. 1974,% 4055,4057,4059; 1975,97 5409. 63 D. N. Kirk and W. Klyne J.C.S.Perkin I 1974 1076.