Anti-Diabetic Activity and Nuclear Magnetic Resonance (NMR) Characterization of Natural Esters from Hexane and Dichloromethane Crude Extracts from Calyces of Hibiscus sabdariffa Linn

Abstract

Non-polar crude extracts obtained from the calyces of Hibiscus sabdariffa Linn. (Roselle) and their α-glucosidase inhibitory activity has been investigated. Roselle extracts potentially act as an anti-diabetic activity. However, most of the previous studies on Roselle were just focused on the polar crude extracts. Therefore, hexane and dichloromethane crude extracts were selected for these study. 3 kg of samples were air dried at room temperature, ground and serially extracted by solid-liquid extraction technique using hexane and dichloromethane. Compounds were isolated and purified by various chromatographic techniques. Their structures were elucidated with 1D and 2D-NMR, and other spectroscopic methods including MS, IR and UV as well as comparison with data reported in the literature. The phytochemical study has led to the isolation of three compounds namely squalene, triglyceride fatty acids (consist of ethyl oleate, ethyl linoleate and γ-ethyl linolenate) and ethyl stearate. Based on the literature, this is the first reported squalene isolated from the calyces of Roselle. The α-glucosidase inhibitory activity on the crude extracts was conducted and showed moderate inhibitory activity was detected on hexane crude extract. Thus, results from this study can be used as future references for the discovery of natural esters and the potential of Roselle as an anti-diabetic source.