Identification of Potential Antioxidant and Hypoglycemic Compounds in Aqueous-Methanol Fraction of Methanolic Extract of Ocimum canum Leaves

Abstract

Ocimum canum belongs to a genus of aromatic annual and perennial herbs and shrubs in the family of Lamiaceae. It is native to Africa and cultivated commonly for its culinary and medicinal value. In a previous study, we reported the antioxidant and hypoglycemic activity of the crude methanol extract and the solvent fractions of Ocimum canum leaves.This present study was aimed to partially isolate and identify some bioactive compounds in the aqueous-methanol solvent fraction of methanol extract of Ocimum canum leaves. The sample was fractionated via silica gel-column and solvent system to yield many fractions which was pooled using analytical TLC. The pooled fractions were screened for antioxidant activity (DPPH scavenging assay and Ferric Reducing Power) and ability to reduce fasting blood glucose (FBG). The most active sub fraction was analysed with LC-MS and GC-MS to identify the active compounds. A total of 197 fractions were collected and pooled to seven (7) subfractions. Subfraction OC4 showed the best activity with IC50s 48.6±6.6µg/ml and 15.2±3.9µg/ml for DPPH scavenging and Ferric Reducing Power assays respectively, a 37% reduction in FBG and a concomitant increase in insulin level in treated diabetic rats. The LC/GC-MS analysis revealed tentatively the following compounds: Diosmetin, Dihydroquercetin, Digalloyl glucose isomer, Ananaflavoside isomer, Kaempferol glucoside embinin isomers, eugenol, hexadecanoic acid, 9,12 octadecanoic acid, and β-sitosterol. The study corroborates the previously reported antioxidant activity and hypoglycemic potential of the leaves of Ocimum canum and further more identified bioactive compounds that can be isolated and further characterised.