Isolation and Characterization of Antimicrobial Compounds from the Plants, Erythrina Abyssinica dc. and Chasmanthera Dependens Hochst

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Irungu, Stanley
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Infectious diseases account for approximately one-half of all deaths in tropical countries. In industrialized nations, despite the progress made in understanding of microbiology and their pathogenic control, incidences of epidemics due to drug resistant micro-organisms and the emergence of hitherto unknown disease causing microbes, pose enormous public health concerns. Thus, there is need to continue the search for appropriate drugs for anti-microbial treatment without much drawbacks. Historically, plants have provided a good source of anti-infective agents. They are cheap and effective in the treatment of diseases while simultaneously mitigating many of the side effects that are associated with synthetic anti-microbial agents. Phytomedicines derived from plants have shown great promise in the treatment of intractable infectious diseases including opportunistic human immunodeficiency virus (HIV) / acquired immune deficiency (AIDS) infections. The plant species Erythrina abyssinica DC. and Chasmanthera dependens Hoschst have been reported to exhibit remarkable antimicrobial activities and are used as herbal remedies by traditional medical practioners. In this study, the plant extracts from the two species were screened for their antibacterial activity against selected strains of bacteria, including Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus, antifungal activities against Trichophyton mentagrophytes and yeasts (Candida albicans). The isolation and purification of bioactive compounds was done using solvent partition and chromatography: CC, PTLC and VLC. Structure characterization was carried out using standard spectroscopic methods: 1H NMR, 13C NMR, DEPT, COSY, HSQC, HMBC and NOESY. 1,5,4′-trihydroxy-5′-prenylchalcone (131), 2',3′,4′,7-tetrahydroxy-5'-prenylflavanone (132) and 2'-methoxy-nor-glycyrrisoflavanone (134) were isolated from Erythrina abyssinica. 2,3-epoxycolumbin (furano diterpenoid) (137) was isolated from Chasmanthera dependens. One compound 2'-methoxy-nor-glycyrrisoflavanone (134) showed high activity against the gram-positive bacteria Staphylococcus aureus with inhibition zone of 15 mm. The DCM crude extract of E. abyssinica stem barks had activity against Staphylococcus aureus and the fungi Trichophyton mentagrophytes with inhibition zones of 10 and 16 mm, respectively. The hexane extract of root tuber of C. dependens was highly active against Staphylococcus aureus and Trichophyton mentagrophytes with inhibition zones of 16 and 23 mm, respectively. The study demonstrated that there is need for further investigation and isolation of more pure compounds from both plants. In addition the crude extracts and the pure compounds be subjected to further bioassay against other disease causing microbes.