Antioxidant and antibacterial activities of constituents and hemi-synthetic derivatives from Senna siamea (Lam.) H. S. Irwin & Barneby (Caesalpiniaceae) Antioxidant and antibacterial activities of constituents and hemi-synthetic derivatives from Senna siamea

Abstract

Eleven compounds (1-11) were isolated from the methanolic extract of leaves and bark of <i>Senna</i> <i>siamea</i>. Benzylation of compound 2 gave two new hemi-synthetic derivatives: 4'-O-benzylvitexin (12) and 7,4'-O-dibenzylvitexin (13). The structures of these compounds were established on the basis of their spectroscopic (1D and 2D NMR) and mass spectrometric (FAB-TOF-MS) data. The extracts, fractions, some of the isolated compounds as well as hemi-synthetic derivatives were evaluated for their antibacterial activity using broth microdilution method. They were also tested for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging potential and ferric reducing antioxidant power (FRAP). The ethyl acetate fraction of the stem bark showed moderate activity) against E. faecalis and P. mirabilis with MIC value of 256 μg/mL. Compound 6 showed moderate activity toward P. mirabilis (MIC = 64 μg/mL). The methanolic extract from bark (EC50 = 1.58 ± 0.25) μg/mL, its ethyl acetate (EC50 = 1.12 ± 0.67) μg/mL and n-BuOH fractions (EC50 = 1.02 ± 0.87) μg/mL as well as n-BuOH fraction from leaves (EC50 = 1.24 ± 0.33) μg/mL were more active against DPPH compared to vitamin C. Compound 4 was the most active against DPPH (EC50 = 1.05 ± 0.38) μg/mL.