Structures of three new steroidal sapogenins fromDioscorea prazeri

摘要

1560 J.C.S. Perkin IStructures of Three New Steroidal Sapogenins from Dioworea prazeriBy Krishnamurthy Rajaraman, Ashok Kumar Batta, and Srinivasa Rangaswami,' Department ofThree new steroidal sapogenins isolated from the rhizomes of Dioscorea prazeri have been shown on the basis ofchemical and spectral evidence to be (25R)-spirost-5-en-3~,14-diol (I), (25R)-14-hydroxyspirost-4-en-3-one(11), and (25R)-14- hydroxy-5p-spirostan-3-one (111).Chemistry, University of Delhi, Delhi-110 007, IndiaFROM the petroleum extract of Dioscorea prazeri we haveisolated three new substances which gave typicalsteroidal colour reactions, showed i.r. absorptionscharacteristic of spirostanols 1 of the iso-series and gavemass spectral fragments (a-c) associated with spiro-stanols.2 They are therefore steroidal sapogenins andhave been designated as prazerigenins A-C.Prazerigenin A, CZ7H4204, formed a monoacetate whosei.r. spectrum showed a band due to a free hydroxy-group, which was lost as water on treatment withphosphoryl chloride-pyridine.The genin gave a positivetest for unsaturation with tetranitromethane. Oppen-auer oxidation yielded an ap-unsaturated ketone(u.v. and i.r.), and oxidation with chromic oxide gave aproduct with U.V. absorption typical of a steroidalA4-3,6-dione.3 On treatment with t-butyl chromate theacetate gave an a@-unsaturated ketone ( A5-7-one), aswould be expected of compounds of the cholesterolacetate type.4 These results led to the conclusion thatthe genin has a 3-hydroxy-group and a 5,6-double bond.The tertiary hydroxy-group could be at one of positions8, 9, 14, 16, 17, 20, and 25.Position 25 was ruledout by the presence of the fragments a-c in the massspectrum and of a three-proton n.m.r. doublet a t6 0.79 characteristic of C(27)H3.5 Position 20 was ruledout by the observation of a C(21)H3 signal as a doubletat 6 0.97. Positions 20 and 25 were also ruled out bythe spectral properties of the (two) dehydration productsof the acetate. A 20-hydroxy-compound would ondehydration have given a compound,G whichwould be recognisable by the i.r. absorption character-istic of an exocyclic methylene group. A 25-hydroxy-compound would be expected to give two isomers(Aza- and A%-) both having a CH3*C= g-roup.' The twoanhydro-acetates did not show evidence for either of theabove-mentioned features.Position 17 was ruled outsince our compound would then be identical withpennogenin, whereas direct comparison showed that theywere different. Position 16 was ruled out since thel6a-proton n.m.r. signal was present at the character-istic * position 6 4.63. The choice thus lay among 8,9, and 14. By comparison of the n.m.r. 6 values of theM. E. Wall, C. R. Eddy, M. L. McClennan, and M. E.Klumpp, Analyt. Chem., 1962,24,1337; R. N. Jones, E. Katzenel-lenbogen, and K. Dobriner, J . Anzer. Chem. SOC., 1963, 75, 158.C. Djerassi and W. H. Fad, Oyg. Mass Spectrometry, 1970, 3,1187.B. Achari, E. Ali, P. P. G. Dastidar, and S. C . Pakrashi, J .Indian Chem. SOC., 1974, 51, 419.C.W. Marshall, R. E. Ray, I. Laos, and B. Riegel. J . Amer.Chem. SOC., 1967, 79, 6310.W. E. Rosen, J. B. Ziegler, A. C . Shabica, and J. N. Shoolery,J. Amer. Chem. SOC., 1969, 81, 1687.13 and 10-Me in 0-acetylprazerigenin A with thosecalculated on the basis of Tables furnished by Tori etthe OH was assigned to the 14a-position. On the basisof this structure, two anhydro-derivatives would beexpected, namely and A14. The former wouldhave no additional vinylic proton in comparison with theparent genin, while the latter would have one, at C-15.In fact the genin acetate yielded two anhydro-compoundsof which one but not the other contained an additionalvinylic proton. The genin was catalytically reduced toremove the double bond and then acetylated.The pro-duct was identical with authentic 14%-hydroxytigogeninacetate lo (m.p., [K],, and i.r. spectrum). Hence prazeri-genin A is (25R)-spirost-5-en-3~,14-diol (I).0 m (IY) 5a-H,R = : aiHPrazerigenin B, C,H,04, possessed an ap-unsaturatedCO grouping (u.v., 1.r.) and also a hydroxy-groupresistant to acylation. It was identical with theOppenauer oxidation product of genin A and is thereforeidentified as (25R)-14-hydroxyspirost-4-en-3-one (11).Prazerigenin C, C,,H,O,, has a ketone group in a six-membered ring (i.r.), no unsaturation, and a hydroxy-group resistant to acylation. The ketone was assignedto position 3 since the genin was identical with theproduct of catalytic reduction of prazerigenin B under6 hI.E. Wall and H. A. Walens, J . Amev. Chem. SOC., 1958, 80,7 R. Tschesche and K. H. Richert, Tetrahedron, 1964, 20, 387.8 D. H. Williams and N. S . Bhacca, Tetrahedron, 1965, 21,9 K. Tori and K. Aono, Ann. Reports Shionogi Res. Lab., 1964,lo P. Bladon, W. Mc Meekin, and I. A. Williams, J . Chem. SOC.,1984.1641.14, 136.1963, 67271975alkaline conditions.ll The stereochemistry at C-5 wasdeduced as 9 from the observation that prazerigenin Cwas different from 14a-hydroxytigogenone obtained byoxidation by chromic oxide of dihydroprazerigenin A(52-14). Further, when prazerigenin C was reduced withsodium borohydride and the resulting 3p-alcohol wasacetylated, the product was different from the acetate ofdihydroprazerigenin A. On the basis of these observ-ations, prazerigenin C would be (25R)-14-hydroxy-5p-spirostan-3-one (111).The n.m.r. data were fully inagreement with this structure.db ' e{fi 9pFragments d-h, when present, have the following substituentslunsaturation: 3@-OH, As-, l4a-OH when derived from (I) ;3-0x0, A4-, 14a-OH from (11); 3-oxo-GP-H, 14a-OH from (111),3-oxo-5a-H, 14a-OH from (VI), ~P-OAC-SP-H, 14a-OH from (V)acetate; 3j3-OA4c, A 598(14)- and 3P-OAc, A58l4- from the twoanhydro-compounds.EXPERIMENTAL1T.p.s were taken on a Kofler hot-stage apparatus.Optical rotations were taken for solutions in chloroform.U.V. spectra were recorded for methanolic solutions on aHilgcr-Uvispek spectrophotometer. 1.r. spectra were re-corded on a Perkin-Elmer Infracord 137 instrument forKBr discs.N.m.r. spectra were taken for solutions in[2H]chloroform except where otherwise stated, with tetra-methylsilane as internal standard, on a Varian A-60instrument. All compounds were tested for purity byt.1.c. on silica gel.Isolutiox .-The petroleum extract (6 g) obtained fromthe rhzonies (2.5 kg) of Dioscorea prazeri was taken up inchloroiorm and an excess of methanol was added. Theprecipitated solid was purified in the same manner and theresulting colourless solid (2.0 g) was chromatographed oversilica gel. The initial benzene-ethyl acetate (48 : 2)eluates yielded prazerigenin C (25 mg) and later eluatesyielded prazerigenin B (50 mg). Benzene-ethyl acetate(47 : 3) eluted prazerigenin A (1.6 g).Praserigenin A [(25R)-spirost-5-en-3P, 14-diog had m.p.l 1 I;.Johnson, G. T. Newbold, and F. S. Spring, J. Chenz. SOC.,1954, 1302.1561220-222"; [a],, -84.9" (c 0.73); RF 0.30 (benzene-ethylacetate-methanol, 95 : 5 : 4) (Found: C, 75.0; H, 10.1.C,,H4@4 requires C, 75.3; H, 9.8%); vmX. 3 448, 3 000,1648, 982, 920, 900, 867, 842, and 820 cm-l (900 cm-lband stronger than that a t 920 cm-l) ; m/e 430 (M+, 2%).412 (M - H20, loo), 394 (M - 2H,O, 3), 379 (394 - Me,23), 371 (d, 2), 361 (e, 3), 358 (f, 3), 353 (d - H,O, 4), 343(e - H20, 3), 340 ( f - H,O, 9), 316 (g, 2), 298 (g - H,O13), 287 (h, 1), 283 (g - H,O - Me, 6 ) , 280 (g - 2H,O, 5),269 (h - H,O, 6), 265 (g - 2H,O - Me, 12), 251 (h -2H,O, 6), 139 (a, 93), 126 (b, 30), and 115 (c, 16); acetate(Ac,O-C,H,N; 37 "C; 18 h), m.p.155-158"; [a], - 150.6"(c 0.81) ; RF 0.76 (benzene-ethyl acetate-methanol, 95 : 5 : 3)(Found: C, 73.9; H, 9.6. C2gH4405 requires C, 73.7; H,9.3%); vmax. 3 472, 2 914, 1 718, 1 627, 1 236, 980, 917, 897,870, 841, and 823 cm-l; 6 6.43 (1 H , m, 6-H), 4.63 (2 H,m, 16- and 3-H), 3.50 (2 H, m, 26-H), 2.04 (Ac), 1.05 (3 H,s, 10-Me; calc. 1.03), 0.97 (3 H, d, J 7 Hz, 21-H3), 0.92(3 H, s, 13-Me; calc. 0.91), and 0.79 (3 H, d, J 7 Hz, 27-H,);6 (C,D,N) 5.36 (1 HI m, 6-H), 4.68 (2 HI m, 16- and 3-H),3.48 (2 H , m, 26-H), 2.00 (Ac), 1.13 (3 HI d, J 8 Hz, 21-H3),1.06 (6 H , s, 13- and 10-Me; calc. 13-Me 1.08, 10-Me1.04), and 0.66 (3 HI d, J 6 Hz, 27-H3).Oppenauey oxidation of Prazerigenin A : formation of theA4-3-0?2e (11).A solution of prazerigenin A (0.05 g) andaluminium isopropoxide (0.05 g) in anhydrous toluene(5 ml) was heated to boiling, cyclohexanone (1 ml) wasadded, and the mixture was refluxed for 10 h. The excessof cyclohexanone was removed by steam distillation andthe residue was acidified and extracted with ether. Theextract was evaporated and the residue crystallised fromchloroform-methanol as needles (0.03 g), m.p. 244-247" ;B p 0.40 (benzene-ethyl acetate-methanol, 95 : 5.: 4) (Found:C, 76.5; H , 9.6. C2,H4004 requires C, 75.7; HI 9.3%);A,,, 240 nm (log E 4.13); v,,, 3 505, 1 670, 1 602, 980,920, 900, and 862 cm-l.(25R)- 14-Hydroxyspirost-4-en-3,6-dione from prazerigeninA. A solution of prazerigenin A (0.05 g) in acetone (10 ml)was treated with Jones reagent (containing 25 mg ofCrO,) a t room temperature for 2 h.The product, isolatedin the usual manner, was purified by passage through acolumn of silica gel and crystallised from chloroform-petroleum as light yellow PZates (0.025 g), m.p. 247-260";[a],, -37.5" (c 0.96); RF 0.39 (benzene-ethyl acetate-methanol, 95: 5 : 4) (Found: C, 72.8; HI 9.0. C2,H3,06requires C, 73.3; HI 8.6%); A,,,,. 254 nm (log E 3.99);vmlx. 3 490, 1 680, 1 670, 1 595, 978, 918, 900, and 865 cm-l.7-Oxoprazerigenin A acetate. A solution of prazerigeninA acetate (0.1 g) in carbon tetrachloride (2 ml), acetic acid(1 ml), and acetic anhydride (0.25 ml) was treated a t55-60 OC with a solution containing t-butyl chromate l2 incarbon tetrachloride (0.15 g in 2 ml), acetic acid (0.5 ml),and acetic anhydride (0.25 ml) during 45 min with stirring.Stirring was continued for 10 h at 65 "C, the mixture wascooled to 20 O C and the excess of oxidant was destroyed byadding aqueous 10% oxalic acid (2 ml) during 1 h.Theproduct was isolated by adding water and extracting withchloroform, and crystallised from chloroforni-methanol asplates (0.06 g), m.p. 255-257", [a], -111.4" (c 0.79);RF 0.64 (benzene-ethyl acetate-methanol, 95 : 5 : 3) (Found:C, 71.9; H, 9.0. C2gH,,06 requires C, 71.6; H, 8.7%);Amx. 234 nm (log E 4.13): v,,,,~. 3 500, 1 735, 1 660, 1 610,1 240, 982, 922, 900, and 868 cm-l.l2 A. G. Gonzalez, R. Freire, J. A. Salazar, and E. Suarez,Phytochernistry, 1971,10, 13391562 J.C.S. Perkin IAction of phosphoryl chloride on $razerigenin A acetate.Prazerigenin A acetate (0.15 g) in dry pyridine (4 ml) wastreated with phosphoryl chloride (0.5 ml) at 0 "C and leftat 0 "C for 0.5 h and then at room temperature overnight.The product isolated in the usual way was separated intotwo components by preparative t.1.c.(benzene-ethylacetate, 95 : 5). (25R)-Spirosta-5,8( 14)-dien-3p-yZ acetatehad m.p. 181-184', [a], - 133.3" (c 0.78) (yield 70 mg) ; R p0.66 (benzene-ethyl acetate, 95: 5) (Found: C, 76.5; H,9.6. C2gH4204 requires C, 76.6; H, 9.3%); vmx. 2 941,1 724, 1235, 980, 924, 903, 868, 851, and 816 cm-l; 6 5.37(1 H, m, 6-H), 4.50 (2 H, m, 16- and 3-H), 3.53 (2 H, m,26-H), 2.04 (Ac), 1.02 (3 H, s, 13-Me; calc. 0.97), 0.97 (3 H,d, J 6 Hz, 21-H,), 0.92 (3 H, s, 10-Me; calc.0.92), and0.78 (3 H, d, J 6 Hz, 27-H,); m/e 454 (Mf, 8%), 395(d, 36), 394 (M - AcOH, loo), 379 (394 -Me, lo), 340(g, l), 325 (e - AcOH, 8), 322 (f - AcOH, 6), 311 (h, 4),280 (g - AcOH, 13), 265 ( g - AcOH -Me, 22), 251(h - AcOH, 22), 139 (16), 126 (7), and 115 (10). (25R)-Spirosta-5,14-dien-3P-yZ acetate had m.p. 200-203" ; [a],-17.8" (c 0.90) (yield 40 mg); RF 0.55 (benzene-ethylacetate, 95 : 5) (Found: C, 76.8; H, 9.6%); v,,, 2 950,1725, 1637, 1235, 977, 917, 899, 864, 838, and 814 cm-l;6 5.42 (2 H, m, 6- and 15-H), 4.95 (1 H, double d, 16-H,26-H), 2.08 (Ac), 1.07 (6 H, s, 13- and 10-Me; calc. 13-Me1.04, 10-Me 1.03), 1.02 (3 H, d, J 7 Hz, 21-H,), and 0.82(3H, d, J 6 Hz, 27-H,); m/e 454 (M+, 4%), 395 (d, 32),394 (M - AcOH, loo), 379 (394 - Me, 5), 340 (g, 9),325 (e - AcOH, 5), 322 (f - AcOH, 19), 280 (g - AcOH,34), 265 (g - AcOH - Me, 12), 139 (21), 126 (15), and115 (12).5,6-Dihydvoprazerigenin (14a-Hydroxytigogenin) (IV) .-This was prepared by hydrogenating prazerigenin A (0.1 g)in glacial acetic acid (5 ml) over palladium-charcoal (10% ;0.03 g) for 2 h at atmospheric pressure and room tem-perature.It crystallised from chloroform-methanol asplates (0.09 g), map. 216-218"; [a], -666.4' (c 0.86); Rp0.28 (benzene-ethyl acetate-methanol, 95 : 5 : 4) (Found:C, 75.2; H, 10.5. Calc. for C,,H,,O,: C, 74.9; H, 10.2%)(lit.,lO m.p. 211-212', [a], -58.8') ; acetate (Ac20-C,H,N;37 "C; 18 h), m.p. 192-195"; [a], -65.0" (C 0.96); R p0.72 (benzene-ethyl acetate-methanol, 95 : 5 : 3) (Found :C, 73.1; H, 9.9.Calc. for C29H1605: C, 73.4; H, 9.7%);vmx. 3 580, 1 739, 1 242, 980, 920, 899, and 870 cm-l (i.r.spectrum identical with that of authentic 14a-hydroxy-tigogenin acetate) (1it.,lo m.p. 187-189", [aID - 60.8').(25R)-14-Hydroxy-5a-s~irostan-3-one. An ice-cold solu-tion of compound (IV) (0.03 g) in pyridine (1 ml) wastreated with chromic oxide (0.03 g) in pyridine (1 ml) andleft at room temperature for 18 h. The crude product waschromatographed over silica gel and crystallised fromacetone-petroleum as needles (0.017 g), m.p. 226-228";[a], -45.3" (c 1.06); R p 0.49 (benzene-ethyl acetate-methanol, 95 : 5 : 4) (Found: C, 75.2; H, 10.0. C2,H4,04requires C, 75.3; H, 9.8%); v,, 3 571, 1709, 980, 922,897, and 866 cm-l; m/e 430 (M+, 54y0), 412 (M - H20,25), 402 (M - CO, 14), 397 (M - H,O - Me, lo), 371(d, IS), 361 (e, 13), 358 (f, 48), 316 (g, 36), 298 (g - H20,loo), 287 (h, l l ) , 283 (g - H,O - Me, 34), 269 ( h - H,O,65), 139 (go), 126 (35), and 115 (30).J15,16 8, J16.1, 3 Hz), 4-58 (1 H, m, 3-H)) 3-53 (2 H, m,Prazerigenin B [( 25R)- 14-hydroxys~irost-4-en-3-one] hadm.p. 245-247"; [a], -43.3" (G 0.60); &= 242 nm (log E4.11); v,, 3 500, 1 672, 1 602, 978, 920, 900, and 862cm-l; m/e 428 (M', 9%), 410 (M - H20, 6), 400 (M - CO,1.5), 395 (410 - Me, l ) , 369 (d, 9), 359 (e, 8), 356 (f, 16),(g - H,O, 88), 285 (h, 3), 281 (g - H20 - Me, 19), 267(h - H,O, 18), 139 (loo), 126 (25), and 115 (12), and wasidentical with the Oppenauer oxidation product of prazeri-genin A described earlier (mixed m.p., t.l.c., and i.r.spectrum).Catalytic Reduction of Prazerigenin B .-Prazerigenin B(11) (0.025 g) in dry ethanol (3 ml) was treated withpotassium hydroxide (0.015 g) in dry ethanol (3 ml) andshaken in hydrogen with palladium-charcoal (10% ; 0.01 g)for 2 h at room temperature and atmospheric pressure.The mixture was filtered and the filtrate poured into water;the solid was filtered off and crystallised from acetone-petroleum as needles (0.015 g), m.p.237-240', identicalwith prazerigenin C, described below (mixed m.p., t.l.c.,and i.r. spectrum).Prazerigenin C [( 25R)-14-hydroxy-5~-s~irostan-3-one] (111)had m.p. 237-240'; [a], -48.3" (G 1.16); R p 0.42 (benzene-ethyl acetate-methanol, 95 : 5 : 4) (Found: C, 75.2; H,9.8.C,,H,,O, requires C, 75.3; H, 9.8%) ; v,, 3 597,1 701, 980, 922, 899, and 870 cm-l; 6 4.61 (1 H, m, 16-H),3.43 (2 H, m, 26-H), 1.05 (3 H, s, 10-Me; calc. 1.04), 0.97(3 H, d, J 7 Hz, 21-H,), 0.92 (3 H, s, 13-Me; calc. 0.92),and 0.78 (3 H, d, J 7 Hz, 27-H,); m/e 430 (M+, 17%),412 (M - H20, 6), 402 (M - CO, 4), 397 (412 - Me, 0.5),371 (d, 5), 361 (e, 2), 358 (f, 12), 353 (d - H,O, 0.5), 343(e - H20, l), 340 (f - H,O, 0.5), 316 (g, 20), 298 (g - H20,54), 287 (h, l), 283 (g - H20 - Me, 7), 269 (h - H,O, S),139 (loo), 126 (31), and 115 (16).Reduction of prazerigenin C. To a solution of prazeri-genin C (111) (0.02 g) in methanol (3 ml) sodium boro-hydride (0.03 g) was added and the solution was set asidefor 2 h. The product, isolated in the usual manner, was amixture of two compounds (t.1.c.) in the ratio ca. 9 : 1, butthey could not be separated because of close RF values.The mixture was acetylated (acetic anhydride-pyridine) at37 "C for 18 h. The compounds were separated by pre-parative t .l.c. over silver nitrate-impregnated silica gel.The minor product was amorphous. The major product,(25R)-5P-s@irostan-3P, 14-diol (V), crystallised from chloro-form-methanol as needles (0.012 g), m.p. 189-191";[d, -76.7' (c 0.91); RF 0.77 (benzene-ethyl acetate-methanol, 95: 5 : 3) (Found: C, 73.8; H, 9.8. C,gH&requires C, 73.4; H, 9.7%); v,, 3 600, 1 730, 1 250, 980,920, 900, and 866 cm-l; m/e 474 (M+, 6%), 456 (M - H20,5), 415 (d, 6), 405 (e, l), 402 (f, 14), 360 (g, 6), 342 (g - H,O,69), 327 (g - H,O - Me, 22), 313 (h - H20, 5), 139 (loo),126 (56), and 115 (19).We thank Professor T. R. Seshadri for his interest in thiswork, Dr. A. Akahori for an authentic sample of pennogenin,Dr. P. Bladon for the i.r. spectrum of 14a-hydroxytigogeninacetate, Dr. N. Nand and Dr. T. R. Govindachari for n.m.r.and mass spectra, and Dr. K. N. N. Ayengar for discussions.K. R. thanks the University of Delhi for a research fellow-ship.[4/2486 Received, 28th November, 19741351 (d - H20, 2), 338 (f - HZO, 1.5), 314 (g, 21), 29