Stem bark extracts of Erythrina excelsa (BAK) and their biological activities

The species is known from Southern Nyanza, Migori in Kenya. The extraction of the stem bark was done sequentially using organic solvents starting with the least polar; n-hexane then dichloromethane, ethyl acetate and finally the most polar methanol. Antibacterial and antifungal activities of the crude extract and that of isolated compounds from the stem bark of E. excelsa were investigated. The crude extracts had substantial activity against the tested micro-organisms.  Methanol extract was highly active with inhibition zones of 15 mm against S. aureus and 14 mm against both B. subtillis and E. coli. Ethyl acetate and dichloromethane had mild activity. In antifungal test, methanol extract had highest activity of 15 mm against A. niger and 13 mm against C. albicans. Dichloromethane extract was also active with inhibition zones of 14 mm against A. niger and 12 mm against C. albicans while ethyl acetate had mild activity. A total of five compounds were isolated; glutinosalactone A (1), glutinosalactone B (2), lupinifolin (3), sitosterol (4) and 3β-stigimasterol (5). The compounds were active against the bacterial and fungal test strains used. Glutinosalactone A (1) had an activity of 15 mm against A. niger, 11 mm against both B. subtillis and S. aureas. Glutinosalactone B (2) had a high activity of 11 mm in both B. subtillis and C. albicans. and lupinifolin (3) had mild activity of 9 mm against both A. niger and C. albicans. Stigimasterol and sitosterol had mild activity of 8 mm against A. niger. Key words: Erythrina excelsa, biological activities, ethnobotany, metabolites.