α-Glucosidase Inhibitory Activity of Pyranochromenes and Root Extracts of Tephrosia purpurea

Abstract

Tephrosia purpurea (L.) Pers. (Leguminosae) is a herb found throughout the Indian subcontinent and popularly known as “Sarapunkha” in Sanskrit and "Purple Tephrosia" in English [1]. The plant is used in folk medicine as an antidiabetic, antipyretic, anticancer, and antiulcer agents and is also useful in the treatment of diseases related to oxidative stress, free radical activity, and inflammation [2]. The previous researchers reported that the plant contains prenylated flavonoids, chalcones, and alkaloids as bioactive constitutes [3–5]. Re-investigation of T. purpurea root extract afforded a new pyranochromene (1) and a previously known 5-hydroxytephroapollin (2). Column chromatography was carried out on Kiesigel-60 (230–400 mesh, Merck) and Sephadex LH-20 (Himedia Chemicals, India). TLC was performed on silica gel 60 F254 plates (0.25 mm, Merck Co.), and spots were detected under UV light and colored by spraying with 10% H 2 SO 4 solution followed by heating [3, 5]. The root of T. purpurea was collected in October, 2011, Nanded, Maharashtra, India. A voucher specimen has been deposited in the Herbarium of the School of Life Sciences, SRTM, University, Nanded, India. The isolated compounds were identified by comparing their melting points with literature data and by UV, IR, NMR, and MS spectral analysis. However, no research has so far been conducted concerning -glucosidase inhibitory compounds from T. purpurea. In order to investigate the -glucosidase inhibitory activity of root extracts and compounds from T. purpurea in vitro and in vivo, the -glucosidase inhibitory activity of two isolated compounds (1, 2) along with the root extracts obtained using different solvents like petroleum ether, ethanol, ethyl acetate, methanol, and butanol were studied. The structures of isolated compounds 1 and 2 were identified using spectral, chromatographic methods, and mass spectrometry, 1: 9,10,11-trihydroxy-1H,7aH-pyrano(2,3-c;6,5-f)dichromen-7-one, according to previously published spectral data [6, 7], 2: 5-hydroxytephroapollin, according to previously published spectral data [3, 5]. This study indicates that the isolated compounds and root extract of T. purpurea have excellent antioxidant and -glucosidase inhibitory activity which, in turn, will have therapeutic applications. The data investigated in this study provides the basis for further investigations on this plant for the development of drugs against diseases related to activity of -glucosidase and oxidative stress. Extraction and Isolation. The air-dried roots (5 kg) of T. purpurea were extracted with 95% methanol under reflux condition. After evaporation of the solvents under reduced pressure, the residue (200 mg) was submitted to chromatography over silica gel column and eluted with petroleum ether (PE, 60–90C), CHCl 3 , EtOAc, CH 3 COCH 3 , and CH 3 OH, successively, to yield compounds 1 (62 mg) and 2 (62 mg) [8, 9]. Melting points were recorded in open capillaries with electric melting point apparatus and were uncorrected. IR spectra (KBr disks) were recorded using a PerkinElmer 237 spectrophotometer. 1 H NMR (400 MHz) spectra were recorded on a Bruker Avance spectrometer using DMSO-d 6 as solvent. Mass spectra were