Bioassay Guided Isolation of Angiotensin Converting Enzyme Inhibitor Compound Verbascoside From Potential Clerodendrum Species of North East India

Verbascoside isolated from leaf extract of Clerodendrum inerme was found as an Angiotensin Converting Enzyme inhibitor for the first time. In vitro antihypertensive evaluation of six Clerodendrum species and a multi technique based approach comprising of bioassay guided thin layer chromatography, liquid chromatography-mass spectrophotometry and UV spectrophotometry were used to identify the potential Angiotensin Converting Enzyme inhibitor compound, verbascoside from column fractions of Clerodendrum inerme. The potent sub fraction F5.2.5 showed maximum of 80% ACE inhibition. LC-MS of crude methanol leaf extract revealed presence of mass peaks with 625.3 m/z M+H+ confirming the presence of verbascoside like molecule (exact mass 624.5 m/z) in the sample and most potent sub fraction F5.2.5 displayed the fragmented isotopic mass peaks of Verbascoside (163.2, 325.2, 479.2 and 647.2 m/z M+H+) revealing the Angiotensin Converting Enzyme inhibitor of Clerodendrum inerme is probably a phenyl glycoside like Verbascoside. The identity of the Verbascoside was confirmed finally with the measurement of absorption maxima (-max) and dark brown TLC band of F5.2.5 as compared to the standard reference compound. The result suggests that the antihypertensive effect of Clerodendrum inerme may be, at least in part, due to ACE inhibitor effect of verbascoside in sample.