Isolation, Identification and Biological Activities of the Constituents of Hibiscus rosa-sinensis Leaf Extract

Abstract

Hibiscus rosa-sinensis has over the years been used in the treatment of bacterial infection and oxidative stress related diseases. In this study, the leaf extract of Hibiscus rosa-sinensis (Linn) was investigated for total phenolic content, total flavonoid content, antioxidative potential, acetylcholinesterase inhibitory and antibacterial activities. In vitro bioactivity-guided isolation led to the isolation of compound 1 and a mixture of compounds 2 and 3 from the aqueous methanol fraction. The extract, fractions and isolated compounds were investigated for their antioxidant, acetylcholinesterase inhibitory and antibacterial activities. The crude methanolic extract has the highest phenolic constituents TPC and TFC (86.14±1.67 mg GAE/g and 10.25±7.89 mg QUE/g) respectively. The crude methanol extract also exhibited a higher ferric reducing antioxidant power (FRAP) than the aqueous methanol fraction with a value of  42.19±1.89 mg AAE/g. Mixture of compounds 2 and 3 has the highest total antioxidant capacity TAC (36.06±1.09 mg AAE/g), DPPH free radical scavenging activity (0.09±0.05 mg/mL) and acetylcholinesterase inhibitory AChEI (0.86±0.13 mg/mL) in IC₅₀ activities. The crude extract and compound 1 showed considerable antibacterial activity against Gram+ve strain; Bacillus stereomophillus and Gram-ve strain; Escherichia coli respectively. The isolated compounds were identified using two spectroscopic techniques (IR and NMR). Compound 1 was identified as sucrose, compounds 2 and 3 were identified as scutellarein-6-O-rhamanoside-8-C-glucoside and apigenin-6-C-glucopyranose respectively. This study concluded that crude extract, fractions and isolated compounds showed varying degrees of biological activities ranging from moderate to moderately high activities.