摘要:

1977 1597Chemical Constituents of Gentianaceae. Part 222 Structures of New1,3,5-Tri- and 1,3,5,6,7-Penta-oxygenated Xanthones of Canscora decus-sata SchultBy Shibnath Ghosal,' Kanika Biswas, and Ratan K. Chaudhuri, Pharmaceutical Chemistry ResearchLaboratory, Department of Pharmaceutics, Banaras Hindu University, Vananasi-5, IndiaTwo new xanthone glucosides and two free xanthones, isolated from Canscora decussata, have been identified as1 - glucosyloxy- 3 - hydroxy- 5 - methoxy- (1 ) , 7 - g I ucosyloxy- 1.6-d i hydroxy- 3,5 - d imethoxy- ( 2), 1 .5.6 - tr i h yd roxy-3.7-dimethoxy- (4). and 1.5.7-trihydroxy-3,6-dimethoxy-xanthone (7) on the basis of chemical transformationsand spectral evidence. On the basis of reassessment of the spectroscopic data and additional chemical evidence, ithas been shown that the pentaoxygenated xanthones previously reported to be 1,3,7-trihydroxy-5,6-dimethoxy-xanthone (' Xanthone IV ') and 1.7-dihydroxy-3.5.6-trimethoxyxanthone (' Xanthone XI1 ') are in fact 1.3,5-tri-hydroxy-6.7-dimethoxy- (9) and 1.5-dihydroxy-3.6.7-trimethoxy-xanthone (1 0).respectively. The stucture of1.6.7-trihydroxy-3.5-dimethoxyxanthone (' Xanthone XI I I ') has been confirmed.THE isolation of nearly two dozen polyoxygenatedxanthones,1*2 five triterpene~,~ and loliolide fromCavtscora decussata Schult (Gentianaceae) has beenreported. Further investigation of the alcoholic extrac-tives of the whole plant furnished two new xanthoneglucosides (1) and (2) and two new free xanthones (4) and(7) whose structures have been established as follows.Compound (I) , C,H,O,,, showed U.V.absorptionmaxima characteristic of 1,3,5-trioxygenated xan-thones lv5 (Table 1). In the mass spectrum of theTABLE 1U.V. data of xanthones of C. decussataA,,./nm (log E) (solvent MeOH)248 (4.23), 253sh (4.09j, 275sh (3.83), 310 (3.91)244sh (4.37), 262 (4.42), 277sh (4.01), 315 (4.05)258 (4.55), 285infl (3.96), 328 (4.16), 362 (3.50)258 (4.58), 282infl (4.03), 325 (4.29), 360 (3.58)255 (4.46), 285infl (4.12), 390 (4.25)253 (4.64), 280infl (4.18), 335 (4.11), 355 (3.89)Xanthone(1)(2)(3)(4)(7)(9)(10) 253 (4.48), 280-282 (3.96), 318 (4.21), 328 (4.05)acetate, there was no molecular ion peak, but significantfragment-ion peaks appeared due to a monoacetoxy-monohydroxy-monomethoxyxanthone (m/e 300) andglucose tetra-acetate (m/e 331).Hydrolysis of thexanthone glucoside (1) with emulsin furnished glucoseand a xanthone (M+ 258), m.p. 278-280°. The aglu-cone formed a diacetate and on methylation with etherealdiazomethane gave 1 -hydroxy-3 , 5-dimetho~yxanthone.~The aglucone was, however, different from any of thepreviously reported 1,3,5-monomethoxydihydroxyxan-thones. In the U.V. absorption spectrum of the gluco-side, in ethanolic sodium acetate, there was a batho-lar ion peak in its mass spectrum. It gave a hexa-acetatethe mass spectrum of which showed monohydroxy-di-acetoxy-dimethoxyxanthone (m/e 388) and glucose tetra-acetate (m/e 331) fragments. Hydrolysis of the gluco-side with emulsin furnished glucose and the aglucone (3),which was identical with ' Xanthone XI11 ', previouslyHOHO HO 0 OMeMe0 Me0~ 4 0~ 3 0chromic shift Of the longer maximum by 22 reported from this plant.5,6 The u .~ . absorption spec- nm (310 ---t 332 nm) indicating the presence of a freeacidic hydrolysis of the product gave l-hydroxy-3,5-dimethoxyxanthone ; this shows that the glucosidelinkage is at C-1.Compound (2) , C21H,20,2, did not exhibit any molecu-trum of the glucoside showed a sodium acetate-induced(315 - 334 nm) thereby indicating the presence offree 3- and/or 6-hydroxy group. The absence of asodium acetate-boric acid-induced shift eliminated the3-hydroxy-group. Permethylation Of the glucoside and bathochromic shift of the longer wavelength maximum1 Part 21, S.Ghosal, R. B. P. S. Chauhan, K. Biswas, and2 S. Ghosal and R. K. Chaudhuri, Phytochemistry, 1973, 12,8 S. Ghosal, R. K. Chaudhuri, and A. Nath, Phytochemistry,* S. Ghosal, A. K. Singh, and R. K. Chaudhuri, J . Pharm.R. K. Chaudhuri and S. Ghosal, Phytochemistry, 1971, 10,6 S. Ghosal, R. K. Chaudhuri. and K. R. Markham, J.C.S.R. K. Chaudhuri, Phytochemistry, 1976, 15, 1041.2035. 2425.1973, 12, 1763.Sci., 1976, 65, 1549.Perkin I , 1974, 2838J.C.S. Perkin Ipossibility of an ortho-dihydroxy-system being present.Since ' Xanthone XI11 ' contains a 3-methoxy group,6hence there must be a free 6-hydroxy group. Inassigning the 1,6,7- t rihydroxy-3,5-dimet hox yxant honestructure (3) to ' Xanthone XI11 ', we relied primarily onthe downfield shift of the 8-H signal in the lH n.m.r.spectrum of its triacetate.6 The other possible structure,1,5,6-trihydroxy-3,7-dimethoxyxanthone (4), for ' Xan-thone X I I I ' has new been examined by synthesis.Treatment of 1 -hydroxy-3,5,6,7-tetrame t hoxyxan t honewith sulphuric acid gave, by selective 5,6-bis-de-O-rneth-ylation,' the xanthone (4), which was different fromrespect to signals of acetoxy-groups at other positions(8.g.1-, 3-, 6-, and 7-, which showed shifts of <l-2 Hz).This phenomenon could be attributed to shielding bythe pyrone ring of the 5-acetoxy protons.1° In thehexa-acetate of the xanthone glucoside (2) the twoaromatic acetoxy-signals appeared as a singlet at 6 2.45.Compound (4), Cl5HI2O7, showed a close similarity inits U.V.absorption maxima (Table 1) to ' XanthoneXI11 '.596 The di- and tri-methyl ethers were identicalwith l-hydroxy-3,5,6,7-tetramethoxy- and 1,3,5,6,7-pentamethoxy-xanthone respectively. Compound (4)responded positively to a Tollens test and showedTABLE 260 MHz lH N.m.r. spectral data for the acetates of 1,3,5,6,7-pentaoxygenated xanthones *Acetate of xanthoneAssignment (2)l-Subst. 2.45 (OAC)2-H 6.65 t$-Subst. 4.03 (OMe)4-H 6.83 t5-Subst. 3.98 (OMe)6-Subst. 2.45 (OAC)7-Subst. 2.0-2.18-H 7.45[ (OAc) 41(3)2.45 (OAc)6.65 t4.03 (OMe)6.82 t3.96 (OMe)2.48 (OAc)2.45 (OAc)(4)2.43 (OAc)6.65 t3.93 (OMe)6.81 t2.36 (OAc)2.45 (OAc))3.93 (OMe)(12)2.46 (OAc)6.60 t2.46 (OAc)6.86 t6.2(O*CH,*O)2.46 (OAc)(7)2.45 (OAc)6.65 t3.90 (OMe)6.81 t2.36 (OAc)3.96 (OMe)2.48 (OAc)(9)2.45 (OAc)6.72 t2.48 (OAc) .6.85 t2.36 (OAc)3.96 (OMe)3.96 (OMe)7.60 7.68 7.66 7.70 7.68* 6 Values; solvent CDCl,; internal standard Me4% t J 2 Hz.(10)2.45 (OAc)6.65 t3.94 (OMe)6.80 t2.36 (OAc)3.94 (OMe)3.94 (OMe)7.67(11)2.41 (OAc)6.64 t4.08 (OMe)6.78 t4.08 (OMe)2.41 (OAc)4.08 (OMe)7.48' Xanthone XI11 ', Further chemical evidence infavour of a 5- rather than a 7-methoxy-group in' Xanthone XI11 ' was obtained as follows.Treatmentof the aglucone (3) with methylene iodide * in the presenceof potassium carbonate afforded the 6,7-methylene-dioxy-derivative (5) which responded to selective mono-demethylation in the presence of hydrochloric acid.This observation indicated that the only methoxy-groupin ring B of the xanthone (3) was situated between twosubstituted oxygen functions, and was therefore at C-5.In the lH n.m.r.spectrum of the hexa-acetate of thexanthone glucoside (2), the 8-H signal appeared at6 7.45, which is normal for a 1,3,5,6,7-pentamethoxy-xanthone. Thus there was no effect of the acetoxy-groups on this proton. The variation in chemical shift of8-H in the acetate derivatives of a number of reference1,3,5,6,7-pentaoxygenated xanthones, observed in thisstudy, is now considered to enable location of the freehydroxy-group(s) in ring B of related pentaoxygenatedxanthones. The 8-H signal shifts by ca.0.23-4.25p.p.m. downfield (relative to its position in the per-methyl ether, 6 7.45) in the case of $-acetoxy- and o$-diacetoxyxanthones, whereas o-acetoxy and om-di-acetoxy-substituents caused a downfield shift of thissignal by only 0.124.15 p.p.m. There is no shift ofthis signal in the case of a m-acetoxy-substituent (Table2). Comparison of the acetoxy signals of these compoundshas also offered a basis for locating free hydroxy-groupsin the parent xanthones. The signal of an acetoxy-group at C-5 appeared at 6 2.36, 4-6 Hz upfield with7 E. D. Burling, A. Jefferson, and F. Scheinmann, Tetra-hedron, 1965, 21, 2653. * 0. R. Gottlieb, M. Taveira MagalhZes, M. Camey, A. A. LinsMesquita, and D. de BarroscorrCa, Tetrahedron, 1966, 22, 1777.bathochromic shifts of 43 and 77 nm in the 385 nmmaximum in the presence of sodium acetate-boric acidand aluminium chloride, respectively.These propertiesindicated the presence of two ortho-hydroxy-groups.The aluminium chloride-induced shift was reduced to26 nm in the presence of hydrochloric acid; hence thereis a free l-hydroxy-group. Of the two methoxy-groups,one must be at C-3 and the other at C-5 or C-7. Sincethe xanthone was different from the xanthone (3), itmust be 1,5,6-trihydroxy-3,7-dimethoxyxanthone (4).Chemical evidence in favour of a 7- rather than a 5-methoxy-group was obtained as follows. The xanthone(4) was heated with methylene iodide in the presence ofpotassium carbonate to give the methylenedioxy-derivative (6) which did not undergo any change whenrefluxed with hydrochloric acid.9 The ring B methoxy-group is thus not buttressed by two substituted oxygenfunctions and therefore at C-7.Finally, synthesis ofthis xanthone from 1 -hydroxy-3,5,6,7-t e tramethoxy-xanthone by 5,6-bisde-O-methylation with sulphuricacid established its structure (4).Compound (7), CI5Hl2O7, gave l-hydroxy-3,5,6,7-tetramet hoxyxan thone on methylat ion with etherealdiazomet hane and 1,3,5,6,7-pent amethoxyxant hone withdimethyl sulphate and alkali. It also gave a triacetate.The U.V. maxima of this compound remained unchangedin the presence of sodium acetate, indicating that theC-3 and C-6 oxygen functions are substituted. In thepresence of aluminium chloride, there was a batho-chromic shift of the longer wavelength maximum by20 nm (390 ---t 410 nm) which remained unaffected on0 A.Brossi and S. Teitel, Org. Prep. Procedures, 1969, 1, 171.10 D. K. Holdsworth, Phytochemistry. 1973,l2, 20111977 1599addition of hydrochloric acid. This indicated the pres- EXPERIMENTALence of a l-hydroxy group. The lH n.m.r. spectrum ofthe xanthone showed a one-proton signal at 6 13.03 dueto a chelated hydroxy-group. The 2- and 4-H signalsappeared as meta-split doublets at 6 6.33 and 6.61,respectively; the 8-H signal appeared as a singlet at6 7.11. In the triacetate of the xanthone, the 8-Hsignal was shifted to 6 7.70 owing to the presence ofo- and 9-acetoxy-substituents. The 2- and 4-H signalsin this derivative appeared at 6 6.65 and 6.81, respect-ively, which are normal positions for such protons in1 -acetoxy-3-me t hox yxan t hones.l1 Selective methyl-ation l2 of the xanthone (3) with sodium hydrogencarbonate and dimethyl sulphate in acetone, followed byselective 5-de-O-methylation with hydrochloric acidafforded 1,5,7-trihydroxy-3,6-dimethoxyxanthone, iden-tical with the natural product.' Xanthone IV ' was previously identified,5*6 as1,3,7-trihydroxy-5,6-dimet hoxyxanthone (8). Thisstructure has now been revised to (9) on the basis oflH n.m.r. data of its triacetate, in which the 8-H signalappeared at 6 7.68 (due to $-acetoxy-shift), indicatingthe presence of a 5-hydroxy-group in the parent xan-thone. In conformity with this assignment, one of theacetoxy-signals in the spectrum of the triacetate appearedat 6 2.36 (5-OAc).Reassessment of the lH n.m.r.data of 'XanthoneXI1 ' 5*6 and its diacetate (the latter showing 0.22 p.p.m.downfield shift in the 8-H signal relative to its positionin the case of the permethyl ether) necessitates revisionof its structure to (10). In support of this, the xanthone(4) was selectively 6-O-methylated with dimethylsulphate and sodium hydrogen carbonate to give ' Xan-thone XI1 ' . 5 7 6In a recent paper on the structure of pentaoxygenatedxanthones of Mesua ferrea L., Gunasekera et al. pro-posed l3 a 1,3,6,7,8-oxygenation pattern for their xan-thones (VIIb) and (VIIc) on the basis of a correspondencein properties of these xanthones with two of thoseisolated from Canscora decussata.5 In view of therevised oxygenation pattern (1,3,5,6,7-) , subsequentlyreported for the xanthones of C.decussata,g the penta-oxygenated xanthones of M . ferrea also must have a1,3,5,6,7-0xygenation pattern. Consequently, a re-allocation of the hydroxy- and methoxy-groups in thexanthones of M . ferrea is warranted,The complementary xanthones (3) and (4) have neverbeen found to co-occur in the various batches of C.decussata plants investigated during the past seven years.This observation seems to have a bearing on the bio-genesis of the pentaoxygenated xanthones of C. decussata.It would be difficult to explain, on the basis of a simplephenolic coupling l4 involving the benzophenone (13)(or equivalent), the complete absence of one xanthone(3) or (4) when the other compound is present in appreci-able amount.G.H. Stout and W. J. Balkenhol, Tetrahedron, 1969, 26,1947.l2 K. R. Markham, Tetrahedron, 1965, 21, 1449.U.V. spectra were recorded with a Cary 14 or Spectromom203 spectrophotometer, i.r. spectra with a Perkin-Elmer621 or 257 instrument, mass spectra with an A.E.I. MS-9spectrometer (at 70 eV), and 60 M H z 'H n.m.r. spectra witha Varian A-60 spectrometer. T.1.c. was carried out onsilica gel G (Merck) in the solvent systems (1) CHC1,-HOAc(4 : 1 : Z), and (4) C6H6-HOAc (96 : 4). Spots were detectedby U.V. fluorescence and staining with iodine vapour.Physical data relating t o some of the xanthones were re-ported previou~ly.~,6Extraction Procedure.-In a typical experiment, theconcentrated etha'nolic extract of C .decussata (whole plant ;GU. 1 kg), after removal of mangiferin by filtration, waspoured into aqueous acetic acid (4%; 400 ml). Thesolution was kept overnight a t room temperature, thenextracted with ether (3 1) (fraction A) and ethyl acetate (3 1)(the processing of this fraction was reported previously 6).The acidic layer was then basified (pH ca. 8) with ammonia;a sticky solid separated which was successively extractedwith ether (3 1) and ethyl acetate (6 1) (fraction B) .Treatment of Fraction A .-The solvent was removed underreduced pressure and the brown gummy residue was tritur-ated with benzene (200 ml) and chloroform (400 ml). Thechloroform-insoluble solid on repeated crystallizations frommethanol furnished either xanthone (4) or (7).1,5,6-Trihydroxy-3,7-dimethoxyxanthone (4).This wasobtained as a pale brown solid (0.148 g), sparingly solublein methanol, m.p. 285", RF 0.4 (1) and 0.72 (3); A,,,(EtOH-NaOAc) 255 (log E 4.54), 270-275sh (4.18), and380 nm (4.25), Lx. (EtOH-NaOAc-H,B03) 255 (4.42),282infl. (4.27), and GU. 365sh nm (4.25); 6 [(CD,),SO] 7.11(1 H, s), 6.65 (1 H, d, J 3 Hz), 6.43 (1 H, d, J 3 Hz), and3.95 and 3.90 (6 H); m/e 304 (Mf, loo%), 289(20), 275(24),274(14), 261(30), and 233(10) (Found: C, 58.75; H, 4.3.C15H120, requires C, 59.2; H, 3.95%). The dimethyl ether,prepared with ethereal diazomethane, crystallized fromethanol as yellow needles, m.p. 171-173", identical [m.p.,mixed m.p., RF value (2), and U.V.spectrum] with authenticl-hydroxy-3,5,6,7-tetramethoxyxanthone. The per-methyl ether, prepared with dimethyl sulphate and potas-ium carbonate in anhydrous acetone under reflux (46 h),crystallized from ethanol as yellow needles, m.p. 175O,identical (m.p., mixed m.p., R p value, and U.V. spectrum)with 1,3,5,6,7-pentamethoxyxanthone.6 The triacetate wasprepared by warming the xanthone (4) (0.025 g) with aceticanhydride (5 ml) and pyridine (2 drops) on a steam-bath(4 h). The product crystallized from ethanol as needles (14mg), m.p. 262"; RF 0.6 (4); Lx. (EtOH) 245 (log E 4.22),302 (3.89), and 342 nm (3.56) (Found: C, 58.25; H, 4.45.C21H1,01, requires C, 58.6; H, 4.5%).l-Hydroxy-3,7-dimethoxy-5,6-methylenedioxyxanthone (6).To a mixture of the xanthone (4) (0.020 g ) and potassiumcarbonate (0.5 g) , in anhydrous acetone (1 5 ml) , methyleneiodide (0.5 ml) was added, and the mixture was refluxed on asteam-bath (14 h).After the usual work-up, the productcrystallized from ethanol as pale brown crystals (0.02 g),m.p. 240-242"; RF 0.71 (1); Am,. (MeOH) 235infl (log E4.46), 255 (4.51), 287infl (4.09), 325 (4.17), and 365sh (3.70)(Found: C, 61.1; H, 3.45. C16H1,0, requires C, 60.75;(95 : 5), (2) C6H6-HOAC (99 : l), (3) Bu~OH-HOAC-H~Ol8 S. P. Gunasekera, S. Ramachandran, S. Selliah, and M. S.l4 J. E. Atkinsonand J . R. Lewis, J . Chem. SOC. ( C ) , 1969, 281.Sultanbawa, J . C . S . Perkin I , 1975, 2447J.C.S. Perkin IH, 3.8%).The xanthone (6) remained unchanged whenrefluxed (16 h) with hydrochloric acid (30%).Synthesis of the xanthone (4). l-Hydroxy-3,5,6,7-tetra-methoxyxanthone (0.092 g) was heated a t 75 "C with con-centrated sulphuric acid (s.g. 1.84; 1 ml) for 20 min andthen kept a t ambient temperature overnight. The mixturewas poured on to crushed ice and the precipitate was filteredoff. The solid showed two spots on t.l.c., RF 0.65 and 0.78(3) which were separated by preparative layer chromato-graphy. The component of RF 0.65 was identical with thexanthone (4). The acetate was identical (m.p., mixed m.p.,and RF value) with 1,5,6-triacetoxy-3,7-dimethoxyxanthone.The component of RF 0.78 was a dihydroxytrimethoxyxan-thone (11) (12 mg), m.p. 252-255'; m/e 318 ( M f ) .Onacetylation (acetic anhydride-pyridine) it gave 1,6-diacet-oxy-3,5,7-trimethoxyxantho.ne as straw coloured micro-crystals, RF 0.7 (4); m/e 402 (M+) (Found: C, 59.25; H,4.55. C2,H1,0, requires C, 59.7; H, 4.45%). Thus thedemethylation yielded a mixture of mono- and bis-de-0-methylated .products ; the 6-methoxy-group was demethyl-ated preferentially.1,5,7-Trihydroxy-3,6-dimethoxyxanthone (7). This was ob-tained as a sparingly soluble (in methanol) snuff colouredsolid (0.075 g), m.p. 280-282"; RF 0.68 (1); Amax. (MeOH-NaOAc) 261 (log E 4.48), 327sh (4.52), and 394nm (4.54);A,, (MeOH-AlC1,) 274 (log E 4.53) and 410 nm (4.56);Amx. (MeOH-AlC1,-HC1) 273 (log E 4.53), 292infl (4.60), and414 nm (4.62) (no shift in U.V. maxima with NaOAc-H,BO,) ;6 [CD,),SO] 13.13 (1 H), 7.11 (1 H, s), 6.63 (1 H, d, J 3 Hz),6.35(1H,d, J3Hz),and3.93(6H,s); m/e304(Mf, looyo),289(15), 275(24), 261(51), 246(6), 245(5), 233(20), 218(6),203(3.51, and 159(5) (Found: C, 58.85; H, 4.0.Cl,H1,O,requires C, 59.2; H, 3.95%). The dimethyl ether, preparedwith ethereal diazomethane, crystallized from ethanol as yel-low needles, m.p. 171-173", identical (m.p., mixed m.p., andRF value) with 1-hydroxy-3,5,6,7-tetramethoxyxanthone.6The permethyl ether, prepared with dimethyl sulphate andpotassium carbonate in acetone under reflux (46 h), crystal-lized from acetone as needles, m.p. and mixed m.p. 175".The triacetate was prepared by warming the xanthone (7)(0.025 g) with acetic anhydride (5 ml) and pyridine (2 drops)on a steam-bath (4 h), and crystallized from ethanol asneedles, m.p.265-267"; RF 0.62 (4); Anla,. (MeOH) 242(log E 4.38), 305 (4.04), and 342 nm (3.74) (Found: C, 58.45;H, 4.55. C,~H~,O~O requires C, 58.6; H, 4.2%).Synthesis of the xanthone (7). 1,6,7-Trihydroxy-3,5-di-methoxyxanthone 6 (3) (0.014 g) was selectively 6-O-methyl-ated by refluxing in acetone (10 ml) with sodium hydrogencarbonate (0.22 g) and dimethyl sulphate (0.04 nil) on asteam-bath (4 h). The solution was then filtered and thesolvent removed. The residue was acidified with dilutesulphuric acid and kept overnight at ambient temperature ;a pale brown solid separated, m.p. 220-225"; m/e 318 (M+).This was selectively demethylated with hydrochloric acid(30%) a t 170 "C for 14 h.The solid was filtered off andtriturated with chloroform and methanol. The solidsparingly soluble in methanol (0.008 g), m.p. 279-281";R p 0.68 (1); Lx. (MeOH) 242sh (log E 4.43), 256 (4.48),285sh (4.13), and 390 nm (4.21), was identical with thenaturally occurring xanthone (7). Acetylation of the com-pound (0.005 g) with acetic anhydride (1 ml) and pyrid-ine (2 drops) on a steam-bath (4 h) furnished the triacetate,m.p. 265-267", identical (mixed m.p., t.l.c., and U.V.spectrum) with the triacetate of the naturally occurringxanthone (7).Treatment of Fraction B .-This fraction on concentrationgave a brown solid (0.45 g), which was filtered off. Themother liquor on evaporation afforded a brown gum (0.22 g)(fraction C).l-Glucosyloxy-3-hydroxy-5-methoxyxanthone ( 1).Thebrown gum crystallized from methanol as cream-colouredcrystals, m.p. 210-212"; RF 0.72 (3) ; Amx. (EtOH-NaOAc)245 (log E 4.24), 272 (4.01), 309infl (3.84), and 332 nm (3.87)(Found: C, 54.3; H, 5.05. C2,H2,01,,H20 requires C,54.8; H, 5.0%). The penta-acetate was prepared bywarming the glucoside (0.032 g) with acetic anhydride (5 ml)and pyridine (4 drops) on a steam-bath (4 h), and crystal-lized from ethanol; yield 22 mg, m.p. 158-161"; m/e 331(50%), 300(100), 258(100), 257(45), 229(78), 228(50), 212(35),169(98), 127(38), and 119(95). The permethyl ether,prepared by treatment of the glucoside with sodium hydrideand methyl iodide in tetrahydrofuran a t room temperature,l5was obtainea as a glassy solid.It was hydrolysed withsulphuric acid (3%) to give l-hydroxy-3,5-dimethoxyxan-thone and 2,3,4,6-tetra-O-methylglucose. Hydrolysis of theglucoside (0.035 g) with emulsin, according to a previouslydescribed p r o c e d ~ r e , ~ ~ gave 1,3-dihydroxy-5-methoxy-xanthone and glucose.7-Glucosyloxy- 1,6-dihydroxy-3,5-dirnethoxyxanthone (2).The brown solid crystallized from ethanol; m.p. 220";RF 0.70 (3) ; Amx. (EtOH-NaOAc) 245 (log E 4.41), 275 (4.60),and 334 nm (4.18) (no shift with NaOAc-H,BOJ ; 6 [(CD,),-SO] 13.0 (1 H, s), 7.10 (1 H, s), 6.61 (1 H, d, J 3 Hz), 6.38(1 H, d, J 3 Hz), 4.9-5.07 (1 H), and 3.90 (6 H, s) (Found:C, 51.75; H, 5.35. C21H,,012,H20 requires C, 52.05;H, 4.95%). The glucoside (0.025 g) on warming withacetic anhydride (5 ml) and pyridine (4 drops) on a steam-bath (4 h) followed by the usual work-up gave the hexa-ace-tate, which crystallized from ethanol; yield 0.014 g, m.p.158-161"; m/e 338( loo%), 346(80), 331(48), 304(98),289(20), 275(24), 274(16), and 261(46).Hydrolysis of theglucoside (0.020 g) with emulsin gave 1,6,7-trihydroxy-3,5-dimethoxyxanthone (3) and glucose. The triacetate of theaglucone, prepared by warming with acetic anhydride andpyridine, crystallized from ethanol as needles, m.p. 203-205"; RF 0.51 (4); Amx. (MeOH) 242 (log E 4.35) and 305 nm(3.99) [properties identical with those recorded for thetriacetate of the naturally occurring xanthone (3)].1,5-Dihydroxy- 3-methoxy-6,7-methylenedioxyxanthone (5).To a mixture of the xanthone (3) (0.022 g) and potassiumcarbonate (0.45 g) in anhydrous acetone (15 ml), methyleneiodide (0.3 ml) was added.The mixture was refluxed(14 h) on a steam-bath. After the usual work-up, theproduct crystallized from ethanol as cream-coloured crystals,m.p. 189-190"; RF 0.78 (1). Selective 5-de-O-methylationof the product was carried out by refluxing i t (0.018 g) withhydrochloric acid (30%) for 16 h. After the usual work-up,the yellow 1,5-dZhydroxy-3-methoxy-6, 7-methylenedioxyxan-thone (5) crystallized from methanol; yield 0.016 g; m.p.170-172"; R F 0.6 (1); A,,,. (MeOH) 255 (log& 4.52), 282infl(4.19), and 325 nm (4.31) (Found: C, 59.2; H, 3.45. CI5-H,,O, requires C, 59.6; H, 3.3%).1,3,5-Trihydroxy-6,7-dimethoxyxanthone (9).The isol-ation, physical, and spectral properties of this xanthone(' Xanthone IV ') were reported previo~sly.5~~ The tri-acetate, prepared by warming it (0.020 g) with acetic anhy-dride (5 ml) and pyridine (2 drops) on a steam-bath (4 h),was obtained as a glassy solid on trituration with hexane-l5 S. Ghosal, P. V. Sharma, and R. K. Chaudhuri, Phyto-chemistry, 1975, 14, 26711977 1601methylene chloride; Rp 0.45 (4); m/e 430 (M+) (Found:C, 58.4; H, 4.4. C,,H,,O,, requires C, 58.6; H, 4.2%).1,5-Dihydroxy-3,6,7-trimethoxyxanthone (10). The isol-ation, and physical and spectral properties of this xanthone(' Xanthone XI1 I) were reported previously.6*6 Thediacetate crystallized from ethanol as needles, m.p. 240-243"; Rp 0.52 (4); Am,. (MeOH) 245 (log E 4.41), 270infl(3.98), 304 (4.06), and 342 nm (3.52) ; m/e 402 (M+).Transformation of the Xanthone (4) into the Xanthone (10).--Selective methylation of the xanthone (4) (0.05 g ) wasaccomplished with dimethyl sulphate (0.016 ml) and sodiumhydrogen carbonate (0.89 g) in anhydrous acetone (50 ml)under reflux (4 h). The solution was then filtered andevaporated. The residue was acidified and then extractedwith ether. The ether-soluble solid (0.042 g) crystallizedfrom methanol as pale yellow crystals, m.p. 239-241°,identical with the naturally occurring xanthone (10). Thediacetate crystallized from ethanol as needles, identical(m.p., R p value, and U.V. spectrum) with the diacetate of thexanthone (10).We thank Professor T. R. Govindachari, Ciba-GeigyResearch Centre, Bombay, and Dr. R. K. Chaudhuri,Pharmazeutisches Institut der Universitat, Bonn, for themass and some of the lH n.m.r. spectra. Financial assis-tance from the University Grants Commission, New Delhi,and the Council of Scientific and Industrial Research, NewDelhi, India, is gratefully acknowledged.[6/2026 Received, 1st November, 1976

ISSN:1472-7781    

DOI:10.1039/P19770001597

出版商:RSC    

年代:1977

数据来源: RSC