Bioactivity guided investigation of the stem bark and leaves of Voacanga Africana (Apocynacea)

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MAY, 2016
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Plants since time immemorial have been used for their beneficial effects such as antimicrobial, antioxidant and bacterial resistance modulation. This project presents work on Voacanga africana (Apocynaceae) a local Ghanaian plant, in which the leaves and stem barks were screened for antioxidant and resistant modulatory properties. The antioxidant assay was determined using DPPH scavenging, total phenolic count and total antioxidant capacity. The antimicrobial and bacterial resistance modulation activity was determined using the broth dilution and agar well diffusion methods using S. aureus, E. coli, S. typhi, P. auregenosa, B. subtilis and Candida albicans. Further work was performed by looking at the phytochemical constituents of the extracts and isolates. The antioxidant activity as seen from the DPPH assay was concentration dependent with the methanolic extract of the stem bark showing more activity than the leaf, with Ic50 of 70 and 1605 respectively, whilst that of the standard (ascorbic acid) was 6.980. Antioxidant activity was also found to be very closely related to the amounts of phenolic compounds which were present in both extract from the correlation plots obtained after the total phenolic and antioxidant assays. The leaf extract also showed no antimicrobial activity whilst the stem bark extract showed very significant activity against the chosen microorganisms, with MIC’s of 4mg/ml against a majority of the microorganisms. Also in this work, isolates were chromatographically obtained from the methanolic extracts and bulked into six fractions labelled VAMA01, VAMA02, VAMA03, VAMA04, VAMA05 and VAMA06. Amongst the isolates, VAMA01 and VAMA02 showed significant activity when combined with most used antibiotics including amoxicillin. Most significant result was when 3mg/ml of the extract VAMA01 was combined with 4mg/ml of amoxicillin against E. coli when the individual MIC’s were 4mg/ml and 32mg/ml respectively. Also combining 3mg/ml of VAMA02 with 8mg/ml of amoxicillin was enough to inhibit the growth of P. aeruginosa where the initial MIC’s were 8mg/ml and 64mg/ml respectively. Thus the extracts VAMA01 and VAMA02 were found to possess very significant resistance modulatory activity.
Dissertation submitted to The Department of Pharmaceutical Chemistry of The Faculty of Pharmacy, KNUST in partial fulfilment of the requirements for the award of Master of Philosophy Degree in Pharmaceutical Chemistry.