South African plant extractives. Part III. Helichrysin, a new chalcone glucoside from aHelichrysumspecies

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1976 1819South African Plant Extractives. Part 11I.l Helichrysin, a New ChalconeGlucoside from a He/iChrysum SpeciesBy Winifred G. Wright, Department of Chemistry, University of Natal, Durban, South AfricaLuteolin 7-glucoside, (-) -2-O-methylchiroinositol. and a new chalcone glucoside, helichrysin (1 ), have beenisolated from the flowers of a Helichrysurn species.THE genus Helichrysuin (Compositae) is recorded ashaving ca. 500 species, 200 of them (' everlasting flowers ')in South Africa. The chemistry of the flowers of avarietyidentified as being close to H. cooperi has now beeninvestigated.An acetone extract of the flowers gave the knownluteolin 7-glucoside, (-)-2-0-methylchiroinositol, and anew glycoside, helichrysin, m.p. 246" (decomp.) (C,,H,O,,, 2 H,O), A,, (MeOH) 360 nm, containing one meth-oxy-group T 6.12 (3 H, s).Helichrysin gave a paleyellow spot on a chromatogram, turning orange withammonia vapour, which indicated that it was a chalconederivative.Acidic hydrolysis of helichrysin gave three products :glucose (identified by paper chromatography and by thespecific reaction with glucose oxidase test reagent), achalcone aglycone, helichrysetin, m.p. 328-330" (de-camp.), A,, (MeOH) 358 nm, corresponding to 360 nmfor helichrysin, placing the sugar in ring A,3 and a flava-none Cl6HI4O5, m.p. 265".The U.V. absorption of the flavanone was similar to thatof naringenin (2), indicating a phloroglucinol-derived ringA in the chalcone. The wavelength (A,, 284 nm; cf. 289nm for naringenin) shows a difference in the A rings.There was a small shift to 281 nm on addition of alumin-ium chloride; a compound with a free 5-hydroxy-group shows a large positive shift with this reagent.*The compound was therefore 5-O-methylnaringenin (3).The position of the sugar in helichrysin was determinedby methylation with dimethyl sulphate, giving a productof m.p.178" (decomp.). This was shown to be fullymethylated by the lack of a spectral shift on the additionof alkali to the ethanolic solution. Acidic hydrolysis1 Part 11, K. H. Pegel and W. G. Wright, J . Chem. SOC. (C),1969, 2327.2 J. B. Harborne, ' Comparative Biochemistry of the Flavo-noids,' Academic Ress, London, 1967, p. 78.Ref. 2, p. 82, table 3.3.then gave a methylated chalcone, m.p.125", A,,(MeOH)333 nm, shifted to 390 nm on addition of sodium acetate,indicating a free 4'-OH group.5 This chalcone did notcyclise to a flavanone with acid and must therefore bemethylated at the 2'- and 6'-OH groups, which confirmsthat the free OH group, and hence the glucose residue inhelichrysin, is at position 4'. Helichrysin therefore hasstructure (1) and is 6'-O-methylchalcononaringenin 4'-glucoside. No evidence for the stereochemistry of theglucoside linkage has been obtained.EXPERIMENTALN.m.r. spectra were recorded with a Varian T60 spectro-meter for solutions in dimethyl sulphoxide (internal Me,Sistandard). 3I.p.s were determined with a Kofler hot-stageapparatus. U.V. spectra were recorded for solutions inmethanol (or 95 ethanol when too sparingly soluble).Extvaction.-Helichrysin.Helichrysum. flowers collectedat Umzinto, near Durban, were identified as Helichrysurn ps.aff. H. cooperi Harv. by Dr. 0. M. Hilliard of the NatalUniversity Herbarium, Pietermaritzburg. These weredried, milled, and extracted successively with hexane, ether,and acetone. The acetone extract was evaporated and theresidue (3.5 g ) boiled with water. On cooling, the filteredsolution gave yellow crystals (1 g) which after several re-crystallisations gave helichifysin (78 mg), m.p. 246" (decomp.)(from methanol) Found: C, 54.7, 54.7; H, 5.05, 5.1; m/e(base peak), 286.0828. C22H2,0,,,2H,0 requires C, 54.5;H, 5.8.(MeOH) 236, 272, 296sh, and 360 nm (log E 4.18, 4.12, 4.05,and 4.31), A,, (MeOH-NaOMe) 242sh, 269, 302sh, and382 nm (log E 4.26, 4.29, 3.98, and 4.30), AmX. (MeOH-,41C13)246~11, 274sh, 294sh, 322sh, 350sh, 370sh, and 396 nm (logE 4.43, 4.34, 4.30, 4.29, 4.32, 4.38, and 4.42), Lx.(MeOH-A1C13-HCl) 250sh, 274sh, 294sh, 322~11, 342sh, 362sh, and386 nm (log E 4.46, 4.38, 4.36, 4.34, 4.37, 4.40, and 4.44),Am, (MeOH-NaOAc) 270, 302sh, 322sh, 374, and 446sh nm(log E 4.48, 4.37, 4.36, 4.44, and 4.29)' Amxe (MeOH-NaOAc-H3B0,) 270, 286, and 350 nm (log E 4.28, 4.20, and 4.28); zCI6H,,O5 requires m/e 286.08411; M* 448,2.30 (1 H, S, H-P), 2.40 (1 H, S, H-a), 2.50 (1 H, 9, H-2J2.6q, €3-3 J3,5 2, J3.2 8 Hz), 3.20 (1 H, 9, H-5, J 5 . 3 2 J5.8 8 Hz),3.47 (1 H, d, H-3', J3/,5/ 2 Hz), 3.74 (1 H, d, H-5 J5/,3/ 2 Hz),2, J2,3 8 Hz), 2.65 (l H, q, H-G, Je.2 2, J6.5 Hz), 3.07 (l H,5.00 (1 H, s, glucosyl H-1), and 6.12 (3 H, s, ORIe).A cold water extract of theresidue from acetone extraction was taken nearly to drynessin vacuo.(- ) -2-O-Methylchiroinositol crystallised fromthe residue and was isolated with the aid of a little acetone.Sublimation gave diamond-shaped crystals, n1.p. 195",identified by X-ray crystallography (space group P2,, a =(-)-2-O-MethyZchiroinositol.8.7, b = 7.2, c = 6.7 A, p =Ref. 2, p. 90.5 T. J. Maybry, K. R. Markham, and M. B. Thomas, ' Sys-tematic Identification of Flavanoids,' Springer-Verlag, Berlin.1970, p. 228.6 ' Crystal Data Determinative Tables, ' U.S. Department ofCommerce, Washington, 3rd edn.. vol. 1, p.-M-97J.C.S. PerkinJ.uteoEin 7-glucoside. The residue from the first crystal-lisatian of helichrysin was extracted with ethyl acetate;evaporh;eion gave yellow crystals of luteolin 7-glucosideJm.p. 256O, identical (m.p., colour tests, u.v., and 1H n.m.r.data) with an 2uthentic sample.Hydrolysis of -Yelichrysin.-Helichrysin (10 mg), 6hydrochloric acid (22 ml), and enough methanol to causecomplete dissolution of the chalcone were heated on awater-bath for 1 h, cooled and set aside in a refrigeratorovernight. Helichrysetin (b'-O-methylchalcononaringenin)separated from the solution and crystallised from methanolin pale yellow needles (4 mg), n: p. 328-330" (decomp.).Testing with aniline acetate showed the absence of carbo-hydrate, and the colours in visible Xght and under U.V.light were the same as those for helichiysin, showing thatthe aglycone still had a chalcone structbre (Found: M',286.0828.Cl,H,,O5 requires A!?, 286.0841) A,, (MeOH)240sh, 256sh, 270,298sh, and 358 nm, Am, (Me9H-NaOMe)274, 330sh, and 408 nm, A,,, (MeOH-AlCl,) 210, 232sh, 272,298sh, 324sh, 374sh, and 416nm, Am=* (MeOH-AiCl,-HCl)198, 232sh, 260sh, 273sh, 294sh, 324sh, and 360 nn:, ADZ(MeOH-NaOAc) 266, 320sh, 386, and 430sh nm, Am=(MeOH-NaOAc-H,BO,) 255 and 368 nm. Extraction ofthe aqueous residue with ether gave 5-O-methylnaringenin(2 mg), m.p. 265" (from ether) (Found: C, 67.2; H, 5.0;A!?+, 286. C16H1405 requires C, 67.1; H, 4.9; M , 286),Ima, (MeOH) 284, 326sh, and 370sh nm, hmx. (MeOH-NaOiMe) 246, 280sh, and 320 nm, kx.(MeOH-AlCl,) 281,320sh, and 364 nm, A, (MeOH-AlCl,-HCl) 282, 320sh,and 362 nm, A,, (MeOH-NaOAc) 284sh, 322, and 380sh nm,h,, (MeOH-NaOAc-H,BO,) 284 and 332sh nm. Theaqueous residue from another, similar, hydrolysis wasextracted with ethyl acetate to remove aglycones and thencarefully neutralised with aqueous sodium hydroxide. Theresidue obtained by evaporation of the solvent and thoroughdrying was extracted with hot dry pyridine. The solventwas removed and the small residue dissolved in three dropsof water. This solution reacted positively to two differenttest papers employing glucose oxidase as a specific test forglucose (Clinistix, Ames Co., and Test Tape, Lilly Labora-tories).Methylation of Helichrysk-Dimethyl sulphate (0.5 ml),helichrysin (1 17 mg) , and anhydrous potassium carbonate indried acetone (170 ml) were refluxed until the yellow colouhad disappeared, and then set aside overnight.The potassium carbonate was filtered off and washed once with acetone. The colourless solution was evaporated under higlvacuum, and methanol was added to the residue. Palyellow crystals separated. Recrystallisation from methanagave the methylated compound (16.7 mg), m.p. 178' (decomp.), Lx. (EtOH) 243, 266, 284sh, and 330 nm (nochanged with addition of sodium methoxide). Under u.vlight, a solution in ethanol gave a brilliant fluorescent blucspot, which was unchanged on exposure to ammonia.4'-Hydroxy-2',4,6'-tri-O-methylchalcononaringenin.-Themethylated helichrysin (16.7 mg) was heated on a water-bat1with hydrochloric acid (6 ; 40 ml), with addition of ethanountil complete dissolution was achieved.Heating wa:continued for 7 h, and the solution was then set aside for tdays. Extraction with ether and crystallisation frommethanol gave fine long needles, m.p. 125O, (MeOH)243, 266, 300sh, and 333 nm, Am (MeOH-NaOMe), 243sh,256, 295sh, and 395 nm, A,, (MeOH-AlC1,) 243, 266,300sh, and 334 nm, A,,, (MeOH-AlCl,-HCl) 243,266, 300sh,334, and 410sh nm, Am (MeOH-NaOAc) 255sh, 264sh,290sh, 347sh, and 390 nm. Under U.V. light a spot of thesolution in methanol gave a brilliant fluorescent blue colour,changing to pale green on exposure to ammonia.Quantitative Hydrolysis of He1ichrysin.-A solution ofhelichrysin (20 mg) in hydrochloric acid (5; 50 ml) washeated on a water-bath for 2 h. T.1.c. showed hydrolysisto be complete. The solution was cooled, extracted withether and ethyl acetate to remove aglycones, neutralised,concentrated , and titrated against a standardised Fehling'ssolution. The precipitated copper(1) oxide was equivalentto 6.84 mg of glucose (Found: 34.2 glucose. C22H24010,-2H20 requires 37.3 for 1 mol. equiv. of glucose).I thank Dr. M. Laing and Mrs. P. Sommerville for thecrystallographic identification of ( -) -2-O-methylchiroino-sitol, Mr. H. A. Candy for collecting the Helichrysumflowers, Mr. H. A. Candy and Dr. K. H. Pegel for theirinterest in the research, the University for a research grant,and the C.S.I.R. for mass spectra.6/1737 Received, 10th September, 1975