Quercetin, a minor constituent of the antihyperglycemic fraction of Bauhinia monandra leaf

Diabetes mellitus is a metabolic disorder with symptoms of hyperglycemia. It has been estimated that by 2030 there will be over 4.8 million people with diabetes mellitus in Nigeria. Bauhinia monandra Kurz (Fabaceae), known as ‘‘Abafe’’ in the Nigerian Yoruba tribe, is ethnomedically used in Puerto Rico and Nigeria for the management of diabetes. The leaves of B. monandra have been reported to contain b-carotene, fatty acids, quercetin (1), rutin (2; quercetin-3-O-rutinoside), and 3,4¢,5,7-tetrahydroxyflavone. Antidiabetic activities have been reported for stem bark and leaf extracts, as well as the antioxidant constituents of the leaves. A leaf methanolic extract was shown to have antihyperglycemic actions in vivo, whereas its purified subfractions were both hyperglycemic and antihyperglycemic. Rutin, with in vitro insulin inhibitory activity, was the only compound isolated from the most active butanolic fraction and its isolation was given as a confirmation of similar activity for the hyperglycemic subfractions of the butanolic fraction. To explain the insulin-stimulating activities of the other subfractions, in the present study the butanolic fraction was further investigated chromatographically to identify its insulinotropic constituent(s). The detailed analytical methods, including the solvents and materials used, were as described previously. Analytical thin layer chromatography, HPLC, reversephase column chromatography,H-nuclear magnetic resonance (NMR), and C-NMR were performed and positive (Na) and negative (HCOOH) electron spray impact mass spectroscopy (ESIMS) spectra were obtained as described previously. The leaves of Bauhinia monandra were identified and collected in Obafemi Awolowo University (OAU), Ile Ife, Nigeria, in December 2002. The most active antihyperglycemic butanolic fraction was obtained and purified as reported earlier. As reported previously, the BMBu5–10 subfraction (54 mg) yielded 16-mg precipitate and 38-mg filtrate. Further purification of this filtrate using semipreparative HPLC yielded 16.2 mg of a compound identical to the precipitate, which had been characterized as 2 (rutin). Using the same chromatographic procedure, another compound (14.2 mg) was isolated as a minor component of the filtrate. The ultraviolet, infrared, mass spectrometry, and NMR spectra, especially correlations obtained from H-H-homocosy, heteronuclear multiple bond connectivity (HMBC) and heteronuclear multiple quantum connectivity (HMQC) heterocosy spectra, of this minor component were in agreement with that of 1 (quercetin). Quercetin (1) was isolated from the BMBu5-10 subfraction. The composition of this subfraction was therefore determined as 1 (14.2 mg; 26%) and 2 (32.2 mg; 60%). Moderate in vitro insulin-stimulating and significantly high antihyperglycemic activities have been reported for the n-butanolic fraction of B. monandra leaf. Activitydirected chromatographic purification of this fraction gave subfractions BMBuF7 and BMBuF7C, which, at successively lower doses, demonstrated high antihyperglycemic and in vitro insulin-stimulating activities, comparable (P > 0.05) with those of glibenclamide. Correspondence Adeleke C. Adebajo, Department of Pharmacognosy, Faculty of Pharmacy, Obafemi Awolowo University, Ile Ife, Nigeria. Tel. : +234 803 3679 390 Email: caadebajo@yahoo.com Received 21 February 2012; revised 11 June 2012; accepted 23 June 2012. doi: 10.1111/j.1753-0407.2012. 00222.x Journal of Diabetes 4 (2012) 439–441