Isolation And Phytochemical Screening Of Potential Anti-Hiv And Antimicrobial Compounds From The Leaves Of Maerua Schinzii And Catophractes Alexandri

ABSTRACT

The validation of traditional medicines involves the isolation and characterization of bioactive compounds and the subsequent evaluation of their safety and efficacy. Traditionally used medicinal plants shortlisted for this study include Maerua schinzii Pax (Capparaceae) and Catophractes alexandri (Bignoniaceae) which are indigenous to Namibia. An extract of the leaves of M. schinzii is ethnomedicinally used to treat cough, headache, earache, acne and skin disorders, whereas the leaves extract of C. alexandri is used to treat worms, sore throat, stomach ache, diarrhoea, and inflammatory conditions. A literature review revealed that these plants have not been subjected to phytochemical analyses. This study therefore attempted the isolation and structure elucidation of the major metabolites from the leaves of the two plants and the subsequent evaluation of their antimicrobial activity as well as inhibitory activity against HIV protease and reverse transcriptase.

Air-dried leaves of each plant were separately pulverized and extracted with an equivolume mixture of dichloromethane and methanol at room temperature for 24 hours on an orbital shaker. The crude extracts so obtained were fractionated using Vacuum Liquid Chromatography (VLC) over silica gel with hexane, dichloromethane, ethyl acetate, acetone, methanol and distilled water - in order of increased solvent polarity. VLC fractions were pooled on the basis of their Thin Layer Chromatography (TLC) profiles and subjected to a combination of Preparative Thin Layer Chromatography (PTLC) and column chromatography techniques.

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A yield of 10.84 mg/g of dry leaves was obtained for the crude extract of M. schinzii, whereas 16.52 mg/g of dry leaves was recorded for the crude leaf extract of C. alexandri. Purification of the VLC methanol fraction of the leaf extract of C. alexandri afforded four subfractions, namely DB1-4. The partially purified compounds CLDB11a and CLDB222 were obtained from DB1 and DB2 respectively, but the compounds could not be characterised due to the small amount isolated. The VLC MeOH fraction of M. schinzii was subjected to PTLC and yielded a partially pure compound, 0.041g MLCB51. Qualitative and phytochemical screen test revealed that the plants under study could serve as a potential source of flavonoids, saponins, bitter principles, alkaloids and coumarins. Semi-purified compounds isolated including crude leaf extracts displayed poor or no inhibitory activity against HIV protease and HIV-1 reverse transcriptase, respectively. Moderate antimicrobial activities were recorded for the semi purified compounds of both plants against four microorganisms: - gram-negative bacteria Klebsiella pneumoniae, Escherichia coli, gram-positive Staphylococcus aureus and fungal strain Candida albicans. However, no compound show activity with E. coli and best activity were recorded with C. albicans. Opportunistic fungal infection considered in the study were Candida albicans for the two plants but C. alexandri stand out for anti HIV and antimicrobial which merit for further study.