Two phenolic glycosides from Curculigo orchioides Gaertn

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Fitoterapia 80 (2009) 279–282

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Fitoterapia j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / f i t o t e

Two phenolic glycosides from Curculigo orchioides Gaertn Stefano Dall'Acqua a,⁎, Bharat Babu Shrestha b, Stefano Comai a, Gabbriella Innocenti a, Mohan Bikram Gewali c, Pramod Kumar Jha b a b c

Department of Pharmaceutical Sciences, University of Padova, Via Marzolo 5, 35131 Padova, Italy Central Department of Botany, Tribhuvan University, Kirtipur, Kathmandu, Nepal Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal

a r t i c l e

i n f o

Article history: Received 23 December 2008 Received in revised form 23 February 2009 Accepted 3 March 2009 Available online 11 March 2009

a b s t r a c t One new glycoside derivative from syringic acid and one new phenol glycoside, curculigoside E (1) and orchioside D (2), were isolated and characterized from the rootstock of Curculigo orchioides collected in the Nawalparasi District (Nepal). The structures of the new isolated compounds were elucidated by means of spectroscopic methods such as 1D, 2D NMR and MS. © 2009 Elsevier B.V. All rights reserved.

Keywords: Curculigo orchioides Nepal Ethnomedicine Isolation

1. Introduction Curculigo orchioides is a medicinal herb distributed throughout Nepal from tropical to subtropical regions [1–3]. It is also diffused in Japan, China, Malaysia, India and Australia. Dried rhizomes are used as tonic in the traditional Chinese medicine [2]. In Nepal, the rootstocks of C. orchioides have several ethnomedicinal uses such as aphrodisiac and tonic as well as against asthma and jaundice [1,2]. Secondary metabolites so far isolated and characterized from ground parts mainly belong to three classes: glycosylated phenolics, triterpenic saponins and aliphatic ketones. Several phenolic glycosides of syringic acid, 2,6-dimethoxybenzoic acid and orcinol (5-methyl resorcinol) derivatives have been previously reported [1–4], and dichloro and methoxy derivatives of the orcinol were also isolated [5]. Moreover orchioside A, curculigosides A–D [5–9], cycloartane type derivatives [10] and other saponins [5,11–13] have also been obtained from C. orchiodes. Phytochemical studies seem to be lacking in the Nepali specimen of this medicinal plant. As a part of our ongoing collaborative work on the medicinal plants from ⁎ Corresponding author. E-mail address: [email protected] (S. Dall'Acqua). 0367-326X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fitote.2009.03.002

Nepal, we undertook the phytochemical work on the ground parts of C. orchiodes collected in the Nawalparasi District, central Nepal. In this paper, we describe the isolation and structural elucidation of one new glycoside derivative from syringic acid and one new phenol glycoside, curculigoside E (1) and orchioside D (2), from the rootstocks of C. orchioides. 2. Experimental 2.1. General Optical rotation was performed on a Jasco P2000 digital polarimeter and UV spectra on a Perkin Elmer lambda 25 spectrophotometer. NMR spectra were obtained with a Bruker AMX 300 spectrometer in CD3OD. HR-MS spectra were recorded on a Mariner Biosystem API-TOF spectrometer. HPLC separations were carried out with an Agilent 1100 series liquid chromatograph equipped with a Diode array detector. Semipreparative HPLC was obtained on a Gilson 305–306 series equipped with a Perkin Elmer spectrophotometer using a Merck Lichrocart C-18 10 μm (10 × 250 mm, ID). GC-MS analysis were performed on a Varian Saturn 2000 GC equipped with ion trap MS detector, using a fused-silica-capillary column (DB-5, 30 m × 0.25 mm × 0.25 μm film thickness, J&W Scientific,

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Folsom, CA, USA). Temperature of the injector was set to 220 °C, temperature gradient was as follows: 120 °C for 2 min, then to 180 °C at 5 °C/min, kept at 180 °C for 10 min and then to 300 °C at 10 °C/min. 2.2. Plant material Rootstocks of C. orchioides Gaerten (Hypoxidaceae) were collected in Nawalparasi District (500 m asl), central Nepal, in August, 2006, and were authenticated by one of the authors (BB Shrestha). The herbarium specimen of the plant has been deposited at Tribhuvan University Central Herbarium (TUCH), Kathmandu. 2.3. Extraction and isolation Ground dried parts of C. orchioides (400 g) were extracted with methanol at room temperature. The yield of extraction was 10% on the basis of dried plant material. The solvent was removed under vacuum and the residue was used for the phytochemical analysis. Methanol extract (15 g) was dissolved in 2000 mL of a mixture methanol/water (1/9) and partitioned with petroleum ether (3 times × 500 mL each) and chloroform (3 times × 500 mL each). The solvents were removed under vacuum. The volume of the aqueous layer was reduced by evaporation under vacuum followed by freezedrying yielding a solid residue of 6 g. The residue (2 g) was applied on a silica gel column (250 mL) and eluted with a mixture of chloroform/methanol/water (10/5/1). Eluted fractions were collected on the basis of their chromatographic behaviour in four groups. Group 3 (450 mg) was subjected to semipreparative HPLC yielding in the isolation of compounds 1 (6.0 mg) and 2 (7.9 mg). Mobile phases were aqueous formic acid (0.1%) (A) and acetonitrile (B), and were eluted with the following gradient: starting with 90% A, 10 min isocratic, and then to 80% A in 65 min. The flow rate was 2.5 mL/min and was monitored at the wavelength of 230 nm. Purity of isolated compounds was checked by HPLC and was N98% on the basis of relative integration. For the determination of sugar residue, the compounds were hydrolyzed (0.5 mL of 3M TFA, 100 °C, 2 h) and then evaporated to dryness under N2. The residue was dissolved in methanol and treated with NaBH4 (5 mg). Acetic acid was added (0.5 mL) and the solvents were dried under N2. The residue was treated with Ac2O (0.5 mL, 100 °C, 1 h). The mixture was cooled in an ice bath, diluted with water and extracted with ethyl ether. The ether phase was used for GC analysis. The acetylated sugars were compared with authentic sample of glucose. For the determination of the absolute configuration of the glucose, a sample of each hydrolyzed compound was treated with R-2-butanol and AcCl (0.1 mL) at room temperature for 24 h. The solvent was evaporated and the sample was acetylated as previously described. The retention time of the R-2-butanol ester acetylated derivative was compared with the one of standard D-glucose derivative [14]. 3,5-Dimethoxy-4-O-[β-D-glucopyranosyl-(1→6)-β-Dglucopyranoside]-benzoic acid 5-methyl-2-O-β-D-glucopyranoside-phenyl ester (curculigoside E) (1) (yield 0.015%). Colorless amorphous solid; [α]25D-27.3 (c 1.10, EtOH); HRAPITOF m/z 789.2445 [M–H]−, (calculated for C34H46O21–H,

789.2453); 1H NMR (CD3OD, 300 MHz) and 13C NMR (CD3OD, 75 MHz) see Table 1. Orchioside D (2) (yield 0.002%): White powder; [α]25D14.4 (c 1.04, EtOH); HRAPITOF m/z 459.1307 [M–H]−, (calculated for C23H24O10–H, 459.1291); 1H NMR (CD3OD, 300 MHz) and 13C NMR (CD3OD, 75 MHz) see Table 1. 3. Results and discussion Compound 1 had a molecular formula of C34H46O21 as deduced from the HRAPIMS. The UV spectrum showed maximum at 265 nm and a shoulder at 300 nm consistent with the presence of phenol derivative. The 1H NMR spectrum revealed the presence of a singlet at δ 7.34 integrating for two protons. Diagnostic HMBC correlations were observed from the singlet at δ 7.34 with carbon resonances at δ 172.6 (C-9), 140.0 (C-4) and 154.3 (C-3 and C-5) supporting the structure of a 4-hydroxy-3,5-dimethoxybenzoic acid moiety. In addition, two doublets at δ 6.41 (J = 8.0) and 6.28 (J = 1.8) and one doublet of doublets at δ 6.37 integrating one proton each and one singlet at δ 2.13 integrating for three protons were observed in the 1H NMR. Long-range HMBC correlations were observed from both the signals at δ 6.28 and δ 6.37 with

Table 1 1 H NMR and 13C NMR data for compounds 1 and 2 (300 and 75 MHz, CD3OD, δ in ppm , number in parenthesis are J in Hz). Compound 1

Compound 2

C

δH

δC

C

δH

1 2 3 4 5 6 OCH3 OCH3 9 1′ 2′ 3′ 4′ 5′ 6′ 7′ GlcI:1′ 2′ 3′ 4′ 5′ 6′

– 7.34 s – – – 7.34 s 3.88 s 3.88 s – – – 6.28 d (1.8) – 6.37 dd (1.8;8.0) 6.41 d (8.0) 2.13 s 5.04 d (7.5) 3.52 dd (8.4;7.5) 3.39 m 3.74 m 3.51 m 4.13 dd (11.8; 2.0) 3.86 dd (11.8; 5.1) 4.46 d (7.5) 3.21 dd (9.00; 7.5) 3.40 m 3.19 m 3.30 m 3.77 dd (11.2; 1.59) 3.77 dd (11.2; 4.4) 4.80 d (7.7) 3.51 dd (10.5;7.7) 3.61 m 3.40 m 3.25 m 3.72 dd (11.1; 2.0) 3.66 dd (11.1; 5.5)

128.5 108.9 154.3 140.0 154.3 108.9 57.8 57.8 172.6 160.9 159.7 110.0 140.3 111.7 110.8 22.2 105.0 74.9 77.1 71.2 76.7 69.8

1 2 3

4.64 d (10.2) 4.00 m 2.28 dd (16.9; 5.46) 2.58 dd (16.9; 4.48) – – – 6.88 d (1.80) – – 6.68 d (8.11) 6.72 m – 6.79 d (1.90) – – 6.64 d (9.0) 6.74 m 4.58 d (7.43) 3.31 m 3.40 m 3.28 m 3.34 m 3.86 dd (11.25;1.50) 3.64 dd (11.25; 4.05)

GlcII:1″ 2″ 3″ 4″ 5″ 6″ GlcIII:1‴ 2″ 3″ 4″ 5″ 6″

104.1 74.9 77.4 72.1 78.0 62.1 110.5 74.6 77.1 72.7 77.7 62.2

4 5 1′ 2′ 3′ 4′ 5′ 6′ 1″ 2″ 3″ 4″ 5″ 6″ 1‴ 2‴ 3‴ 4‴ 5‴ 6‴

δC 76.1 82.3 22.7 85.6 84.6 133.7 116.0 147.7 147.2 116.9 120.4 134.0 120.3 147.8 146.4 116.3 125.3 102.8 74.1 77.5 71.8 77.8 62.7

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carbon resonance at δ 22.2, supporting the presence of a methyl group linked to the aromatic ring. Further long-range correlations were observed from the signal at δ 6.28 with the carbon at δ 160.9 and 159.7 and from the one at δ 6.37 with δ 160.9 supporting the presence of two oxygenated positions. Thus the second aromatic ring was deduced to be a 1,2 dioxy4-methylbenzene. Furthermore, the signals of the anomeric protons at δ 5.04 (J = 7.5), 4.80 (J = 7.7) and 4.46 (J = 7.5) supported the presence of three sugar moieties. Complete sugar assignments were obtained by a combination of COSY, TOCSY and HMQC data (See Table 1). These data were consistent with the presence of three β-glucose moieties. In addition the identity of sugar residues were confirmed by hydrolysis followed by GC analysis. One of the glucose unit was found to have glycosidic linkage at position 6 based on the chemical shift of C-6′ (δ 69.8). Other glycosidation positions were determined by 2D NMR experiments. Diagnostic HMBC correlation was observed from the signal at δ 5.04 and carbon resonance at δ 140.0, as well as NOESY correlation was observed from the same proton signal (H-1′ glc-I) and the methoxy group (δ 3.88) supporting the linkage between glc-I and C-4. Further long-range correlation was observed from the proton signal at δ 4.46 (H-1″ glc-II) with carbon resonance at δ 69.8 (C-6′ glc-I) supporting the 1→6 linkage between glc-II and glc-I. Furthermore, NOESY correlation was observed between the H-1‴ glc-III (δ 4.80) and proton at δ 6.41 (H-6′). HMBC correlation between the same anomeric proton and carbon at δ 160.9 was also found thus establishing all the glycosidation positions in the molecule. With all these evidences, compound 1 was identified as 3,5-Dimethoxy-4-O-[β-D-glucopyranosyl(1→6)-β-D-glucopyranoside]-benzoic acid 5-methyl-2-O-βD-glucopyranoside-phenyl ester. The isolated compound was named curculigoside E.

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Compound 2 had a molecular formula of C23H24O10 as determined from the HRAPIMS. The UV spectrum showed two maxima at 290 and 250 nm consistent with the structure of a phenol derivative. The 1H NMR showed two meta coupled doublets at δ 6.79 (J = 1.90) and 6.88 (J = 1.80), two ortho coupled doublet at δ 6.64 (J = 9.00) and δ 6.68 (J = 8.11) and two overlapping signals at δ 6.72 and 6.74 this latter coupling with the one at δ 6.64 in COSY spectrum. These data along with pertinent HMQC and HMBC correlations revealed the presence of two 1,3,4 trisubstituted aromatic ring. Furthermore, long-range (HMBC) correlations from H-2′ (δ 6.88) and H-5′ (δ 6.68) with carbon resonances at δ 147.2 and 147.7 and from H-2″(δ 6.79) and H-5″(δ 6.74) with carbon resonances at δ 146.4 and 147.8 allowed us to establish the presence of hydroxyl groups in the positions 3 and 4 of both aromatic rings. From the COSY spectrum correlations were found between proton signals at δ 4.64 with δ 4.00 and 2.28–2.58. HMBC correlations were found between H-2′ and H-6′ with C-1 revealing a first linkage between the aromatic ring and the aliphatic chain of the compound. In addition, long-range correlations were observed from the H-3 (δ 2.28–2.58) with quaternary carbon resonances at δ 85.6 and 84.6 and from the H-2″ and H-6″ (δ 6.72) with C-5 (δ 84.6) supporting the presence of the triple bond in the positions 4–5 and the linkage of the penta atomic chain with the second aromatic ring. The COSY, NOESY and HMQC data, as well as hydrolysis experiments, supported the presence of a D-glucose unit. In addition, the coupling constant of the anomeric proton signal (J = 7.43) is indicative of β configuration. Furthermore diagnostic HMBC correlations between H-1 (δ 4.64) and C2‴ (δ 74.1) and between H-2 and C-1‴ (δ 102.8) revealed the glycosidation positions. NOESY correlations (see Fig. 1) were observed between H-2 and H-1‴ supporting the same orientation for this two protons. Furthermore, NOESY cross

Fig. 1. Structures of isolated compounds. Diagnostic NOESY correlations for compounds 1 and 2 are indicated by arrows.

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peaks were observed from H-1 and H-3 indicating the trans orientation for H-1 and H-2. On the basis of the obtained data and the literature for similar compounds [7–9,13] the relative configuration of H-1 and H-2 was established as trans. Our spectral data are very similar to those previously published by Li et al. about crassifoside B [15]. Significant differences were observed for the chemical shifts of H-1 and H-2 (δ 4.81 and 4.56 in crassifoside B and δ 4.64 and 4.00 in our compound) as well as in the chemical shift of C-2 (δ 75.4 in crassifolide B and δ 82.3 in our compound) and in the H-1‴ (δ 4.83 vs 4.58) [15]. Compounds with similar structure were reported from C. orchioides [6] as well as from its other species such as C. recurvata [8], C. pilosa [9] and C. crassifolia [15]. To the best of our knowledge, this is the first report of compound 2, an isomer of crassifoside B [15], from the natural source. We have named compound 2 as orchioside D. Acknowledgments This work has been supported by M.I.U.R. Field work by BB Shrestha was supported by Volkswagen Foundation (Germany) project in Nepal.

References [1] Kubo M, Namba K, Nagamoto N, Nagao T, Nakanishi J, Nishimura H. Planta Med 1983;47:52. [2] Shrestha BB, Dall'Acqua S, Gewali MB, Jha PK, Innocenti G. Biology and phytochemistry of Curculigo orchioides Gaertn. In: Jha PK, Karmacharya SB, Chettri MK, Thapa CB, Shrestha BB, editors. Medicinal plants in Nepal: an anthology of contemporary research. Kathmandu, Nepal: Ecological Society (ECOS); 2008. p. 50–67. [3] Wu Q, Fu DX, Hou AJ, Lei GQ, Liu ZJ, Chen JK, et al. Chem Pharm Bull 2005;53:1065. [4] Valls J, Richard T, Larronde F, Leblais V, Muller B, Delaunay JC, et al. Fitoterapia 2006;77:416. [5] Garg SN, Misra LN, Agarwal SK. Phytochemistry 1989;28:1771. [6] Chen C, Ni W, Mei W. Acta Bot Yunnanica 1999;21:521. [7] Gupta M, Achari B, Pal BC. Phytochemistry 2005;66:659. [8] Chifundera K, Messana I, Galeffi C, De Vincente Y. Tetrahedron 1991;47:4369. [9] Palazzino G, Galeffi C, Federici E, Delle Monache F, Cometa MF, Palmery M. Phytochemistry 2000;55:411. [10] Misra TM, Singh RS, Tripathi DM. Phytochemistry 1984;23:2369. [11] Xu J, Xu R, Li X. Planta Med 1991;58:208. [12] Xu J, Xu R. Phytochemistry 1992;31:2455. [13] Xu J, Xu R, Li X. Phytochemistry 1992;31:233. [14] Li N, Chen J, Zhou J. Helv Chim Acta 2004;87:845. [15] Vinogradov E, Nossova L, Korenevskt A, Beveridge TJ. Carbohydr Res 2005;340:1750.

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