Isolation of Chemical Constituents of Centaurea virgata Lam. and Xanthine Oxidase Inhibitory Activity of the Plant Extract and Compounds.

Abstract

Centaurea virgata Lam. is a species widely used in the traditional medicine in Turkey for the treatment of diabetes, allergy and gastric ulcers. The rationale of its use in the therapy has not been studied previously, therefore the present work aimed at the chemicalpharmacological evaluation of the plant. The xanthine oxidase (XO) inhibitory activity of the MeOH extract and its subextracts (n-hexane, CHCl3 and remaining MeOH-H2O) prepared from C. virgata was investigated in vitro. Moderate activity was exerted in case of the CHCl3 extract (98.9 ± 15.8 μg/mL), therefore constituents of this extract were analysed. Different purification steps, such as VLC, CPC, PLC and crystallization were used for the isolation, and ESIMS, NMR, LC-MS and authentic standards were applied for identification of the compounds. XO inhibitory and DPPH assays were used for evaluation of the bioactivities. Sesquiterpenes [8α-hydroxysonchucarpolide, 8α-(3,4-dihydroxy-2-methylenebutanoyloxy)- dehydromelitensine, and cnicin], flavones (apigenin, hispidulin, salvigenin, eupatorin, 3'-methyleupatorin), and the flavonol isokaempferide were isolated from the active extract. The XO-inhibitory activity of these compounds was analyzed using allopurinol as a positive control (IC50 7.49 ± 0.29 μM). It was found that sesquiterpenes and flavonoids, containing 7- OMe group, are inactive. 7-Hydroxyflavones (apigenin and hispidulin) exerted significant XO inhibitory effect with IC50 values of 0.99 ± 0.33 μM and 4.88 ± 1.21 μM, respectively. Therefore, these compounds are responsible for the XO-inhibitory effect of the extract. The free radical scavenging activity of the isolated flavonoids was determined by DPPH assay, and it was stated that none of the compounds have substantial antioxidant activity, therefore the reduced generation of reactive oxygen species may be the consequence only of XO inhibition.