New Flavonoids from Seed Skin of Xanthoceras Sorbifolia

Short Communication

New flavonoids from seed skin of Xanthoceras sorbifolia

Rashmi 1* and Akito Nagatsu 2

1Chemistry Division, Forest Research Institute, Dehradun-248006, India. 2College of Pharmacy, Kinjo Gakuin University, Oomori, Moriyama, Nagoya 463-8521, Japan.

Accepted 12 January, 2011

From ethyl acetate extract of seed skin of Xanthoceras sorbifolia, one compound with other known compounds was isolated by column chromatography on acetone: water: acetic acid solvent system. Structural elucidation of these compounds was carried out on the basis of Nuclear Magnetic Resonance (NMR) studies, namely 1HNMR, 13 CNMR, HMBC, HMQC and other 2D spectroscopy.

Key words: Xanthoceras sorbifolia, Sapindaceae, seed skin, flavonoids, epigallocatechin.

INTRODUCTION

Xanthoceras sorbifolia also named as Xanthoceras theasapogenolB, 3β,23-di hydroxy-lup-20(29)en-28- sorbifolium belongs to the family Sapindaceae. It is oicacid-23-caffeate have been isolated from fruits and commonly known as yellowhorn and a member of the husks of X. sorbifolia (Li et al., 2005; Li et al., 2006; Chan soapberry family and hence closely related to maples, et al., 2008; Li et al., 2006). horse-chestnuts and lychee (Chen et al., 1985). It is a Saponins are widely present in X. sorbifolia and have kind of woody oil bearing shrub and originated primarily been reported to possess cytotoxic activity. Its wood, at Loess plateau in North of China and Inner Mangolia bark and fruits are used to treat rheumatism, gout and with characters of drought enduring, cold resistant and enuresis of children as a folk medicine (Li et al., 2007). saline alkali enduring. The review of literature indicates The mentally stimulating activity of the fruit extract has the characterization of about 60 chemical constituents in also been reported in the literature (Li et al., 1994). It has the different parts of X. sorbifolia and belong to various been shown that an extract from the husks of X. sorbifolia classes of compounds namely saponins, coumarins and has cytotoxicity towards various human cancer cell lines flavanoids. Earlier Bunkanka saponin A , bunkanka (Chan and Mark, 2006). Since there were no reports on saponin B , bunkanka saponin C, bunkanka saponin D, chemical investigation of seed skin of X. sorbifolia, we 22-angeloyl-21-epoxyangeloyl barringtolgenol C, 21-22- have carried out phytochemical investigation of seed diangeloyl-24-hydroxy-R1-barrigenol, 21,22-diangeloyl- skin. R1-barrigenol, 3-O-[(3-O-α-L-arabinofuranosyl-2-O-β-D- galactopyranosyl)-β-D-glucuronopyranosyl]-21,22-di-O- angeloyl-R1-barrigenol, Xanifolia-Y0, Xanifolia-Y2, EXPERIMENTAL

Xanifolia-Y3, , Xanifolia-Y7, Xanifolia-Y8,, Xanifolia-Y10,, 3-O- β-d-glucopyranosyl (1 →6)-β-d-glucopyranosyl, 28-O- β-d- Collection and preparation of plant material glucopyranosyl(1 →6) [ α-L-rhamnopyranosyl (1 →2)-β-d- The seeds of X. sorbifolia were collected from China. Kernels and glucopyranosyl, 16-deoxy barringtogenol C, 22-acetyl-21- husks were separated manually from seeds and coarsely O-(4 ΄-O-angeloyl) -β-d-fucopyranosyl theasapogenolB, powdered. 16-O-acetyl-21-O-(3 ΄, 4 ΄-di-O-angeloyl)-β-D- fucopyranosyl

Extraction of husks

Dried and powdered husks (146 g) of X. sorbifolia were sequentially *Corresponding author. E-mail: [email protected]. Fax: 91-135- extracted three times with methanol and distilled water at room 2756865. temperature. The extracts obtained were combined and evaporated Rashmi and Nagatsu 1035

OMe singlet due to H-F2, suggested the presence of a flavan- 3-ol moiety with 2, 3-cis (epicatechin type) OH stereochemistry. The chemical shift of H-F2 ( δ4.90) was B the same as that of procyanidin ( δ4.97) and obviously HO O OH more downfield than that of the 4, 6-linked procyanidins A C A-6 and A-7 (Ma et al., 2000). Thus suggesting that the two flavan units are linked through the C-C4 and C-D8 O positions. The order of the two flavan-3-ol units was OH determined and inter flavan linkages were confirmed by HMBC. Thus, the H-B2', -B6' signals of epigallocatechin D at δ6.79 were correlated with the characteristic ether- O OH linked C-C2 at δ98.3. In this manner, epigallocatechin F was assigned as the upper unit and the whole structure was determined as epigallocatechin –(4 β→8, 2 β→O-7)- E OH epicatechin. HO

OH 1 HNMR (500 MHz, CD 3OD) Figure 1. B-3'-methoxy epigallocatechin – (4 β→8, 2β→O-7)-epicatechin. δ2.80 (dd, 1H-F4a), 2.97(dd, 1H-F4b), 4.06 (d, 1H-C3), 4.24(brs, 1H-F3), 4.41(d, 1H-C4), 4.90(s, 1H-F2), 6.00(d, 1H-A6), 6.06(d, 1H-A8), 6.09(s, 1H-D6), 6.79 (d, 2H-B', B6'), 6.82(d, 1H-E5'), 7.02(dd, 1H-E6), 7.15(dd, 1H-B2'), under reduced pressure to yield extract namely 4 and 1.5 g 3.84 (OCH 3). respectively.

13 Examination of methanol extract CNMR(500 MHz, CD 3OD)

Methanol extract was partitioned with hexane (50x3) and aqueous δ29.3 (C-C4), 29.9 (C-F4), 67.0 (C-C3), 64.5(C-F3), 73.9 methanol (50x3) successively. The hexane extract (1.90 g) was (C-F2), 96.5 (C-D6, A8), 96.7(C-A6), 98.3(C-C2), column chromatographed on silica gel and nine pure compounds 100.2(C-D4a), 102.4(C-A4a), 104.2(C-D8), 107.3(C-B2', were isolated by repeated column chromatography, preparative TLC and HPLC. Aqueous methanol extract again partitioned with B6'), 115.6 (C-E2'), 115.7 (C-E5'), 116.0 (C-E6'), ethyl acetate, butanol and water successively. 120.4(C-E1'), 131.2(C-B1'), 132.5(C-B4'), 145.7 (C-E4'), 146.0(C-B3', E3', B5'), 146.3(C-D8a'), 146.8(C-D5), 152.1(C-A5), 152.3(C-D7), 154.2(C-A8a), 156.6(C-A7). Isolation of flavonoids On the basis of the obtained spectral data, the structure of compound A was determined as B-3'-methoxy Ethyl acetate extract (380 mg) was column chromatographed on silica gel and total three compounds were isolated. Out of these two epigallocatechin –(4 β→8, 2 β→O-7)-epicatechin (Figure were found hydroxyl methyl esters and one compound A was 1). Structure of compound A shows that it contains obtained as brown colored solid (30.5 mg) by repeated column proanthocyanidin dimer with epigallocatechin. Several chromatography on acetone: water: acetic acid. recent reviews have documented the importance of proanthocyanidins. These phytochemicals are widely spread throughout the plant kingdom, where they RESULTS AND DISCUSSION accumulate in many different organs and tissues to provide protection against predation. At the same time, Three pure compounds were isolated from ethyl acetate they impart astringency and flavor to beverages such as extract of husks by CC and HPLC. NMR data of these wines, fruit juices and teas and are major quality factors compounds showed that, out of three two are hydroxyl for forage crops. They are increasingly recognized as methyl esters and one compound was found to be having health beneficial effects for humans (Morimoto et flavonoid. Compound A was obtained as brown colored al., 1987; Dixon et al., 2005). Structure elucidation of the solid (30.5 mg) by repeated column chromatography on proanthocyanidin structures in plants is important for 1 acetone: water: acetic acid. Its HNMR data were same understanding potential health beneficial effects of these as those of procyanidin A-2 (Chan and Mark, 2006) in the dietary phytochemicals. region higher than 6.50 ppm. It was evident from spectral data that it is a doubly linked proanthocyanidin dimer with epigallocatechin as one of its flavan-3-ol units, whose H- ACKNOWLEDGEMENTS B2' and H-B6' protons were responsible for the singlet signal observed at δ6.79. The appearance of a broad We are highly thankful to Daiko Foundation Research 1036 J. Med. Plant. Res.

Fellowship Programme, Japan for their financial support. Li W, Li X, Meng DL, Zhang P, Li ZL (2007). Two new Triterpenoids from the carpophores of Xanthoceras sorbifolia Bunge. J. Asian Nat. Prod. Res., 9(1): 7-11. Li XB, Wang HD, Guo Y (1994). Xanthoceras sorbifolia fruit extracts for REFERENCES enhancing mental activity. CN: 1084876, Oct 5 th . Chan PK, Mark E (2006). Proc. Am. Assoc. Cancer. Res., 47: 452-453. Chen YZ, Takeda T, Y.Ogihara Iitaka Y (1985). Studies on the Ma CM, Nakumara N, Hattori M, Kakuda H, Qiao JC, Yu HI (2000). constituents of Xanthoceras sorbifolia Bunge. V. Major Saponins from Inhibitory effects on HIV-1 Protease of Constituents from the Wood of the fruits of Xanthoceras sorbifolia Bunge Chem. Pharm. Bull., 33(4): Xanthoceras sorbifolia . J. Nat. Prod., 63: 238-242. 1387-1394. Morimoto S, Nonaka GI, Nishioka I (1987). Tannins and related Li ZL, Li X, Li LH, Li N, Yu M, Meng DL (2005). Two New Triterpenes compounds. LIX. Aesculitannins, novel proantocyanidins with doubly- from the Husks of Xanthocaras sorbifolia . Planta Medica, 71: 1065- bonded structures from Aesculus hippocastanumm L. Chem. Pharm. 1068. Bull., 35: 4717-4729. Li ZL, Li BZ, Wang SJ, Li N, Wang Y (2006). Triterpenoids from the Dixon RA, Sharma SB, Xie D (2005). Proanthocyanidins- a final frontier husks of Xanthoceras sorbifolia Bunge. J. Asian Nat. Prod. Res., in flavonoid research, New Phytol., 165: 9-28. 8(4): 361-366. Chan PK, Zhao M, Che CT, Mak E (2008). Cytotoxic acylated triterpene saponins from the husks of Xanthoceras sorbifolia . J. Nat. Prod., 71: 1247-1250. Li W, Li X, Yang J, Li LH, Li N, Meng DL (2006). Two New Triterpenoids from the carpophores of Xanthocaras sorbifolia Bunge. Pharmazie, 61: 810-811.