Isolation and HPLC Profiling of Chemical Constituents of Saraca Asoca Stem Bark
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Indian Journal of Chemistry Vol. 55B, March 2016, pp. 353-361 Isolation and HPLC profiling of chemical constituents of Saraca asoca stem bark Furkan Ahmada,b, Laxminarain Misra*a, Rashi Tewaria, Preeti Guptaa, Vivek K Guptaa & Mahendra P Darokara a Chemical Sciences Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226 015, India b Academy of Scientific and Innovative Research (AcSIR), CIMAP-Campus Lucknow 226 015, India E-mail: [email protected] Received 26 December 2014; accepted (revised) 18 January 2016 Saraca asoca (Roxb.) de Wilde, a common tree of India, is popularly used in the ayurvedic and modern herbal systems of medicine for genito-urinary problems of women. In the current herbal market there happens to be mixing of adulterants with authentic S. asoca stem bark. In order to identify the right bark material, there exists hardly any laboratory testing possibilities to authenticate the stem bark samples. The n-hexane, methanol and aqueous methanol extracts have been investigated by isolating and characterizing major compounds and developing the HPLC profiling of methanol and aqueous methanol extracts. The n-hexane, methanol and 60% aqueous methanol extracts of stem bark of S. asoca after isolation, have yielded a total of 17 compounds whose structures were established by spectroscopic methods. A series of experiments were run to develop the HPLC conditions for the chemical profiling of the bark. The n-hexane extract has been found to contain mainly triterpenoids and sterols while methanol extract has yielded several flavanol derivatives along with a few triterpenoids. The aqueous methanol extract afforded flavanol derivatives. Out of the isolated compounds, ursolic acid, lupeol, glochidiol, 5,3'-dimethoxy epicatechin, 3'-eoxyepicatechin-3-O-β-D-glucopyranoside, 3'-deoxycatechin-3-O-α-L- rhamnopyranoside and epigallocatechin have been isolated from S. asoca bark for the first time. HPLC profiling of methanol and aqueous methanol extracts of the bark has been developed by using mainly the isolated compounds as references. The percent composition of the major compounds was determined by HPLC and can be used to monitor the possible adulterations in the commercial bark materials. The antibacterial tests showed that the methanol and aqueous methanol extracts and few compounds have mild activity on some of the bacterial strains whereas they did not show any antifungal activity. Keywords: Saraca asoca (Roxb.) de Wilde. syn. S. indica Linn., antibacterial activity, HPLC profiling Saraca asoca (Roxb.) de Wilde syn. S. indica Linn. is enzymes, decreased protein bound carbohydrates, locally named as ashoka and belongs to the family urinary collagen and serum cytokines as well as Caesalpiniaceae. It is an ever green tree distributed normalized histopathology of joints7 and did not show in India, Bangladesh, China and Malaysia. It is any toxicity8. found throughout India, especially in Bihar, Odisha, Earlier, the scantly pursued phytochemical studies Konkan, Deccan, Karnataka, West Bengal and in the on the stem bark of S. asoca have shown the presence central and eastern Himalayas up to an altitude of of campesterol, β-sitosterol, stigmasterol, leucocyanidin, 750 meters1,2. Ayurvedic physicians, even now, use leucopelargonidin, procyanidin B1, procyanidin B2, ashoka in treatment of various diseases, especially catechin, epicatechin, gallaocatechin9-13 and antioxidant the gynaecological disorders. It is popularly used in and DNA topoisomerase active lignan glycosides2,14. the pharmaceutical preparations like asokarishta and However, in previous publications the comprehensive asokagirtha, which are prescribed against leucorrhoea, isolation of the compounds from different extracts and haematuria, menorrhagia and other diseases of genito- their HPLC profiling was not studied. In continuation urinary system of women3,4. Phenolic glycosides from of our interest in the chemical investigation of S. asoca have shown oxytocic activity5. The bark Indian medicinal plants15-19, recently the presence of extracts have shown antioxidant activity due to the anti-inflammatory activity, flavanol glycosides and presence of phenolics and flavonoids6. The MeOH pinitol from S. asoca bark have been reported20,21. extract has been shown to exhibit strong antibacterial The present paper is the continuation of further and antifungal activities1. It has been recently reported investigations leading to a detailed isolation and that the MeOH extract reduced paw swelling, identification of a number of compounds from the increased body weight, reduced level of lysosomal n-hexane, methanol and aqueous methanol extracts of 354 INDIAN J. CHEM., SEC B, MARCH 2016 S. asoca stem bark. Their isolation, characterization spectra and compared with those reported in the by spectroscopic methods and HPLC profiling literature30-32,2,33. of methanol and aqueous methanol extracts are discussed in this paper. Biological activities Previous studies have shown that the extracts of Results and Discussion S. asoca bark possess anti-inflammatory activity34. Characterization of isolated compounds Our recent publication on the bioassay guided The stem bark of Saraca asoca after successive investigation of methanol and aqueous methanol extracts has confirmed that the flavanol glycosides extractions by non-polar to polar solvents has yielded 20,21 three extracts, the n-hexane, methanol and 60% and pinitol were the active principles . Some aqueous methanol. The n-hexane extract after studies on the antimicrobial activity of extracts of flowers and buds35, leaves, stem and flowers36,37 and chromatographic separations afforded a triglyceride, 38 viz. 1-oleo-dipalmitin (2), triterpenoids, viz. ursolic regenerated bark have earlier been done. We have acid (1), lupeol (3), glochidiol (7) and sterols, viz. also tested the extracts and some of the isolated campesterol (4), β-sitosterol (5), stigmasterol (6). compounds for a detailed antibacterial study of Out of these, ursolic acid (1), 1-oleo-dipalmitin (2), S. asoca bark using disc diffusion assay and MIC. lupeol (3), glochidiol (7) have been isolated for the It was observed that the hexane extract was inactive first time (Figure 1 and Table I) from this plant. since no growth inhibition zone was found against The structures of these compounds were confirmed any bacteria whereas the MeOH extract showed the by extensive use of spectroscopic methods, especially net zone of growth inhibition of 2 mm against NMR and comparison with the data available in our Salmonella typhimurium and Staphylococcus aureus library and reported in the literature22-28. which is considered as inactive. The aqueous The methanol extract after rigorous chromatographic methanol extract showed 2-5 mm diffusion against separations, has yielded terpenoids, ursolic acid (1) following bacteria i.e. Salmonella typhimurium, Bacillus and lupeol (3) along with several flavan-3-ol subtilis, Staphylococcus epidermidis, Staphylococcus derivatives, viz. leucopelargonidin (8), leucocyanidin aureus. Among the isolated compounds, epicatechin, (9), 5,3'-dimethoxy epicatechin (10), epicatechin (11), catechin, 3'-deoxyepicatechin-3-O-β-D-glucopyranoside catechin (12), 3'-deoxyepicatechin-3-O-β-D-glucopyranoside and 3',5-dimethoxy epicatechin did not show any O L (13), 3'-deoxycatechin-3-O-α-L-rhamnopyranoside (15), inhibition whereas lyoniside, 3'-deoxycatechin-3- -α- - epigallocatechin (16), gallocatechin (17) and lyoniside rhamnopyranoside and gallocatechin showed mild (14). Among them, 5,3'-dimethoxy epicatechin (10), 3'- activity against some of the strains (Table II). deoxyepicatechin-3-O-β-D-glucopyranoside (13), 3'- The MIC of these samples against same bacterial deoxycatechin-3-O-α-L-rhamnopyranoside (15) and strains also did not show promising results. The epigallocatechin (16) are now being reported from S. aqueous methanol and methanol extracts showed asoca20 (Figure 1 and Table I). The structures of these more than 1.0 mg/mL MIC for all the strains tested compounds were confirmed by the interpretation of (Table III) whereas some of the isolated compounds their IR, NMR and mass spectra which were also viz. epicatechin, catechin, 3'-deoxyepicatechin-3-O-β- compared with the data available in the D-glucopyranoside and 3',5-dimethoxy epicatechin literature23,24,29-32,2,33. also showed MIC mostly more than 1.0 mg/mL. Aqueous methanol extract afforded flavan-3-ol The aqueous methanol extract and gallocatechin derivatives, viz. epicatechin (11), catechin (12), showed MIC against Bacillus subtilis as 250 mg/mL. 3'-deoxyepicatechin-3-O-β-D-glucopyranoside (13), These experiments clearly indicated that the bark of epigallocatechin (16), gallocatechin (17) lyoniside S. asoca has no strong antibacterial activity against (14), 3'-deoxycatechin-3-O-α-L-rhamnopyranoside several bacterial strains available with us. (15). Among them, 3'-deoxyepicatechin-3-O-β-D- The methanol and aqueous methanol extracts and glucopyranoside (13), epigallocatechin (16) their column chromatographic fractions after testing gallocatechin (17) and 3'-deoxycatechin-3-O-α-L- against Candida albicans (MTCC183) showed that rhamnopyranoside (15) are being reported for the none of them has a MIC below 250 µg/mL. Therefore, first time20 (Figure 1 and Table I). The structures the extracts cannot be considered as an antifungal were proved by recording their IR, NMR and mass agents against C. albicans. AHMAD et al.: SARACA ASOCA STEM BARK 355 Figure 1 — Chemical structures of isolated