Abstract
This project sought to isolate, characterise and evaluate the antimicrobial potency of flavonoids from Erythrina species. The stem barks of Erythrina plants (E. abyssinica and E. addisoniae) were collected, authenticated, washed and dried. The dried plant material was pulverised and subsequently extracted using methanol. The extract was then subjected to column chromatography over silica gel and eluted with different solvents such as ethyl acetate, dicholoromethane and hexane. The various fractions obtained were screened for flavonoids and the flavonoid fractions were subjected to antibacterial and antifungal bioassays. Further purification of the flavonoids was achieved with the use of preparative high-performance liquid chromatography. Upon evaporation of solvent, some fractions yielded crystals of pure compounds. These pure compounds were then characterised using spectroscopic techniques such as nuclear magnetic resonance (NMR), ultraviolet/visible spectroscopy, fourier-transform infrared spectroscopy (FT-IR) and mass spectrometry. The samples were also analysed using single crystal X-ray crystallography. The methanol extract of the stem bark of E. abyssinica yielded three isoflavones. The first compound, 3-(1-benzofuran-6-yl)-8,8- dimethyl-9,10-dihydro-4H-pyrano[2,3-f]chromen-4-one, is a new isoflavone which has a benzofuran ring. The structure was elucidated on the basis of spectroscopic data and confirmed by single crystal X-ray crystallography. It showed significant antimicrobial activities against some selected bacteria and fungi. The second compound, Jamaicin (3- (4-methoxy-1,3-benzodioxol-5-yl)-8,8-dimethyl-2,3-dihydro-4H,8H-pyrano[2,3- f]chromen-4-one), was isolated for the first time from E. abyssinica (It had been reported from other plants). It showed moderate activities against the selected microbes. Its minimum inhibitory concentration (MIC) value of 125 µg/mL against Enterococcus faecalis was less than the amounts of the standard control drugs (streptomycin and nalidixic acid) required to inhibit the bacterium. ..
M.Sc. (Chemistry)