An acylated flavone C-glycoside from Glycyrrhiza eurycarpa
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Pergamoa 0031~9422(94)EOOS7-Y Phytdwmurry. Vol. 36. No. 4. pp. 1089. IWO, 1994 Copyn,# 0 1% Ektir Scieaa Lid Printed I” Great Britain. All ri&hu reserved 0031-9422194 s7.00+0.00 AN ACYLATED FLAVONE C-GLYCOSIDE FROM GLYCYRRHIZA EUR YCARPA MING LIU, QIN LIU, YONG-LONG LIU.* CUI-YING Hou* and TOM J. MAewt Department of Botany, University of Texas at Austin, Austin, TX 78713, U.S.A.; *Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Beijing 100094, People’s Republic of China (Received 13 September 1993) Key Word Index-Glycyrrhira eurycurpa; licorice; Leguminosae; flavone C-glycoside; apigenin 6-C rhamnoside-8-C-[6”‘~3-hydroxy-3-methylglutaroyl)-glucoside]. Ah&net-A new acylated flavone C-glycoside, apigenin 6-C-a-L-rhamnopyranoside-8-C-[6”’-(3-hydroxy-3-methyl- ghrtaroyl)-j?-D-ghrcopyranoside], was isolated from rhizomes of Glycyrrhiza eurycarpa and its structure was established on the basis of spectroscopic data. Licorice is one of the most important traditional Chinese herbal medicines and three species, Glycyrrhiza uralensis, G. injlata and G. glabra, have been recorded in Chinese Pharmacopoeia for medicinal uses. Glycyrrhiza eury- carpa P. C. Li, a recently described species from the Gansu Province and Xingjiang Autonomous Region, People’s Republic of China [ 11, has also sometimes been used medicinally because of its phenotypic similarity to G. injata and G. glabra. Chemical studies [2,3] indicated that G. eurycarpa also has similar chemical constituents to those reported for G. intata and G. glabra, therefore, it may have similar medicinal value. As a part of our continuing chemical studies of the genus Glycyrrhiza we report here the isolation and identification of a new acylated flavone C-glycoside (1) from G. eurycarpa. The acyl group was identified as 3-hydroxy-3-methylglutaric acid, a side chain not commonly found in plant com- pounds [4]. RESULTS AND DISCUSSION The UV spectra of 1 indicated a typical apigenin-type structure: addition of NaOMe caused 60 nm batho- chromic shift of band II indicating the OH-4’ is free; OH-5 is also free based on the AICl, and AICl, + HCl spectra; addition of NaOAc produced an 8 nm batho- chromic shift which is characteristic for a free OH-7 [53. The ‘H NMR spectrum did not exhibit signals for pro- tons at the 6 and 8 positions, instead two sugar anomeric proton signals were observed at 64.74 and 5.02. There- fore, it was concluded that 1 is an apigenin with sugar moieties at both the 6 and 8 positions. The 13CNMR spectrum showed, in addition to 15 aglycone carbon tAuthor to whom correspondence should be addressed. signals, 12 sugar carbon signals which were assignable to one rhamnosyl and one glucosyl moiety. Compound 1 was readily identified as a C-glycoside since the ‘%NMR spectrum exhibited the signal for the C-l” of the rhamnosyl group at 677.2 and the signal for the C-l”’ of the glucosyl moiety at 673.5. An additional six carbon signals at 6172.6, 170.5, 68.9, 45.5, 45.3 and 27.4 were assignable to a 3-hydroxy-3-methylglutaroyl group [4]. Alkaline hydrolysis of 1 afforded 3-hydroxy-3-methyl- glutaric acid, which was identified by co-TLC with an authentic sample. This acyl group must be attached to C- 6”’ of the glucosyl moiety since the C-6”’ signal of the glucosyl group appeared downfield 2.5 ppm while the C- 5”’ signal shifted upfield 3.5 ppm [3]. The remaining question at this point was the position of attachment of the two sugars. This was determined by comparing the 13C NMR spectrum of 1 with published data for isoviol- anthin (apigenin 6-C-rhamnoside-8-C-glucoside) [3] and violanthin (apigenin 6-C-glucoside-8-C-rhamnoside) [6]. The C-6 and C-8 signals of 1 at 6 106.9 and 104.3 matched those of isoviolanthin; for a violanthin-type structure, the C-6 and C-8 signals would have occurred at around 6 109.3 and 101.9, respectively. Thus, 1 was established as apigenin &C-a-L-rhamnopyranoside-8-C-[6”‘43-hydroxy- 3-methylglutaroyl~B-D-glucopyranoside], a structure not previously reported. The FAB-mass spectrum of 1 gave the [M]’ peak at m/z 722 in accord with the assigned structure. EXPERIMENTAL Mp: uncorr. Collection, extraction and purification. Rhizomes of GIycyrrhiza eurycarpa were collected by the senior author in Jinta County, Gansu Province, People’s Republic of China in August 1986 and a voucher is deposited in the Herbarium of the Institute of Medicinal Plant Develop- 1089
Transcript of An acylated flavone C-glycoside from Glycyrrhiza eurycarpa
Pergamoa 0031~9422(94)EOOS7-Y Phytdwmurry. Vol. 36. No. 4. pp. 1089. IWO, 1994 Copyn,# 0 1% Ektir Scieaa Lid
Printed I” Great Britain. All ri&hu reserved 0031-9422194 s7.00+0.00
AN ACYLATED FLAVONE C-GLYCOSIDE FROM GLYCYRRHIZA EUR YCARPA
MING LIU, QIN LIU, YONG-LONG LIU.* CUI-YING Hou* and TOM J. MAewt
Department of Botany, University of Texas at Austin, Austin, TX 78713, U.S.A.; *Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Beijing 100094, People’s Republic of China
(Received 13 September 1993)
Key Word Index-Glycyrrhira eurycurpa; licorice; Leguminosae; flavone C-glycoside; apigenin 6-C rhamnoside-8-C-[6”‘~3-hydroxy-3-methylglutaroyl)-glucoside].
Ah&net-A new acylated flavone C-glycoside, apigenin 6-C-a-L-rhamnopyranoside-8-C-[6”’-(3-hydroxy-3-methyl- ghrtaroyl)-j?-D-ghrcopyranoside], was isolated from rhizomes of Glycyrrhiza eurycarpa and its structure was established on the basis of spectroscopic data.
Licorice is one of the most important traditional Chinese herbal medicines and three species, Glycyrrhiza uralensis, G. injlata and G. glabra, have been recorded in Chinese Pharmacopoeia for medicinal uses. Glycyrrhiza eury- carpa P. C. Li, a recently described species from the Gansu Province and Xingjiang Autonomous Region, People’s Republic of China [ 11, has also sometimes been used medicinally because of its phenotypic similarity to G. injata and G. glabra. Chemical studies [2,3] indicated that G. eurycarpa also has similar chemical constituents to those reported for G. intata and G. glabra, therefore, it may have similar medicinal value. As a part of our continuing chemical studies of the genus Glycyrrhiza we
report here the isolation and identification of a new acylated flavone C-glycoside (1) from G. eurycarpa. The acyl group was identified as 3-hydroxy-3-methylglutaric acid, a side chain not commonly found in plant com- pounds [4].
RESULTS AND DISCUSSION
The UV spectra of 1 indicated a typical apigenin-type structure: addition of NaOMe caused 60 nm batho- chromic shift of band II indicating the OH-4’ is free; OH-5 is also free based on the AICl, and AICl, + HCl spectra; addition of NaOAc produced an 8 nm batho- chromic shift which is characteristic for a free OH-7 [53. The ‘H NMR spectrum did not exhibit signals for pro- tons at the 6 and 8 positions, instead two sugar anomeric proton signals were observed at 64.74 and 5.02. There- fore, it was concluded that 1 is an apigenin with sugar moieties at both the 6 and 8 positions. The 13CNMR spectrum showed, in addition to 15 aglycone carbon
tAuthor to whom correspondence should be addressed.
signals, 12 sugar carbon signals which were assignable to one rhamnosyl and one glucosyl moiety. Compound 1 was readily identified as a C-glycoside since the ‘%NMR spectrum exhibited the signal for the C-l” of the rhamnosyl group at 677.2 and the signal for the C-l”’ of the glucosyl moiety at 673.5. An additional six carbon signals at 6172.6, 170.5, 68.9, 45.5, 45.3 and 27.4 were assignable to a 3-hydroxy-3-methylglutaroyl group [4]. Alkaline hydrolysis of 1 afforded 3-hydroxy-3-methyl- glutaric acid, which was identified by co-TLC with an authentic sample. This acyl group must be attached to C- 6”’ of the glucosyl moiety since the C-6”’ signal of the glucosyl group appeared downfield 2.5 ppm while the C- 5”’ signal shifted upfield 3.5 ppm [3]. The remaining question at this point was the position of attachment of the two sugars. This was determined by comparing the 13C NMR spectrum of 1 with published data for isoviol- anthin (apigenin 6-C-rhamnoside-8-C-glucoside) [3] and violanthin (apigenin 6-C-glucoside-8-C-rhamnoside) [6]. The C-6 and C-8 signals of 1 at 6 106.9 and 104.3 matched those of isoviolanthin; for a violanthin-type structure, the C-6 and C-8 signals would have occurred at around 6 109.3 and 101.9, respectively. Thus, 1 was established as apigenin &C-a-L-rhamnopyranoside-8-C-[6”‘43-hydroxy- 3-methylglutaroyl~B-D-glucopyranoside], a structure not previously reported. The FAB-mass spectrum of 1 gave the [M]’ peak at m/z 722 in accord with the assigned structure.
EXPERIMENTAL
Mp: uncorr. Collection, extraction and purification. Rhizomes of
GIycyrrhiza eurycarpa were collected by the senior author in Jinta County, Gansu Province, People’s Republic of China in August 1986 and a voucher is deposited in the Herbarium of the Institute of Medicinal Plant Develop-
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Short Reports
ment, Chinese Academy of Medical Sciences, Beijing. The rhizomes were extracted with EtOH. The EtOH soln was coned under vacuum until only H,O remained. Then the remaining soln was partitioned between H,O and CH,Cl,, EtOAc, and n-BuOH, respectively. From the n-BuOH extract 1 was obtained from a Polyclar AT column eluted with an EtOH-H,O gradient.
Apigenin 6-C-a-L-rhamnopyranoside-8-C-~6”’-(3-hydroxy-
3-methylg/utaroy&/Il-D-glucopyranoside] (1). Yellow pow- der, mp 196-199”, soluble in MeOH. FAB-MS m/z (rel. int.): 722 CM] + (l), 721 [M - H] + (5). UV iy::” nm: 270, 334; +NaOMe: 278, 328, 394; +AICI,: 270, 302, 338, 386sh; +AICI, + HCI: 270, 302, 342, 386sh; + NaOAc: 278,3Wh, 382; + NaOAc+ H,BO,: 274, 330. ‘H NMR (100 MHz, DMSO-d,, TMS, ppm): b 13.94 (1 H. s, OH-S), 7.95 (2H,d,J=8SHz, H-2’. H-6’), 6.92 (2H,d,J=8.5 Hz,H-3’. H-5’), 6.80 (lH,s,H-3). 5.02 (lH,hr s,H-1” of Rham),4.74(1H,d,J=g.OHz, H-l”‘ofGlc), 1.25(3H,br, Me of Rham) and 1.15 (3H,s, Me of 3-hydroxy-3- methylglutaroyl group). 13C NMR (25 MHz, DMSO-d,. TMS, ppm): 6163.7 (C-2), 102.3 (C-3), 181.8 (C-4), 157.1 (C-5), 106.9 (C-6), 161.8 (C-7), 104.3 (C-8), 154.6 (C-9), 103.1 (C-lo), 121.1 (C-l’), 128.5 (C-2’, 6’), 115.9 (C-3’, 5’), 161.2 (C-4’), 77.2 (C-l” of Rham), 74.3 (C-2”), 73.9 (C-3”), 71.9 (Cd”), 71.7 (C-5”), 18.3 (C-6’). 73.5 (C-l”’ of Glc), 70.5 (C-2”‘). 78.3 (C-3”‘), 68.9 (C-4”‘). 78.3 (C-5”‘), 63.9 (C- 6”‘). 170.5 (C-l”” of 3-hydroxy-3-methylglutaroyl group), 45.5 (C-2”“), 68.9 (C-3”“). 45.3 (C-4”“) 172.6 (C-5”“) and 27.4 (C-6”“).
Alkaline hydrolysis of compound 1. The 3-hydroxy-3- methylglutaric acid moiety on the glucosyl group was identified after alkaline hydrolysis of 1 [7]. A 40 ~1 sample from a coned MeOH-H,O soln of 1 was mixed with 100 ~1 of 2 M NaOH in a sealed vial filled with N,. The mixture was allowed to stand at room temp. for 2 hr and
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then the solution was neutralized with 120 ~1 of 2 M HCI. The 3-hydroxy-3-methylglutaric acid was then extracted into Et,O. The Et,0 soln was evapd to dryness under a stream of N,. The dried residue was redissolved in a few drops of MeOH and the soln subjected to co-TLC with a standard sample of 3-hydroxy-3-methylglutaric acid from Sigma. The silica gel GF,,, TLC plate was developed with EtOH NH,OH (19: I) and the spots were visu- alized under UV light at 254 nm.
Acknowledgement-This work was supported at the Uni- versity of Texas at Austin by the National Institutes of Health (GM-35710) and the Robert A. Welch Founda- tion (F-130).
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