Phenolic compounds isolated from A. adianthifolia and P. angolensis have shown potency to quench free radical species and inhibit microbial growth due to their ability to donate either hydrogen atom or electron. 3-methylquercetin showed the highest radical scavenging activity (RSA) with minimum inhibition quantity (MIQ) of 0.5 µg, followed by epicatechin, 5-methoxyluteolin, isookanin, melacacidin and 2-O-methylisoliquiritigenin with MIQ of 1 µg each. Calycosin and angolensin were least active (MIQ 5 µg). 3′,4′-dihydroxy substitutions on B ring; C-3 & C-7 hydroxy substitutions on rings C and A respectively; C-2/C-3 double bond conjugated with a carbonyl function at C-4 were responsible for the enhanced RSA of the flavonoids.1 The two hydroxy groups diversely oriented and the C-2/C-3 double bond which allowed for the delocalization of electrons from B ring is believed to have influenced the RSA of chalcone 2-O-methylisoliquiritigenin compared to angolensin.2 Protocatechuic acid, 3-(4-hydroxy-3,5-dimethoxyphenyl)-2-oxiranemethanol and 3-(4-O-β-D-glucopyranosyl)phenylpropanol showed RSA with MIQ’s of 0.5 µg, 1 µg and 5 µg respectively. The number, site of carboxylic acid and hydroxy substitutions on protocatechuic acid influenced its activity. Glycosylation and lack of hydroxy substitutions lowers RSA of benzonoids.3 The triterpenoids were structurally not electron donors hence showed no RSA. Using agar over lay method for the antimicrobial assay, 3-methylquercetin exhibited good activity against Gram positive bacteria (B. subtilis & S. aureus) with MIQ of 5 µg but demonstrated weak activity against fungal strain (C. albicans - MIQ 50 µg) and no activity against the Gram negative bacteria (P. aeruginosa & E. coli – MIQ ˃100 µg). Angolensin showed better antimicrobial activity over 2-O-methylisoliquiritigenin. α,β-unsaturation; 2′,4′ and 2′,6′-dihydroxy on B ring; 5,7-dihydroxy on A ring were considered crucial features for both structure stability and vital for enhanced antimicrobial activity of flavonoids. Weak-to-poor antimicrobial activity (MIQ 50-100 µg) was observed for the benzonoids despite the presence of some vital structural requirements such as carboxylic acid function and two hydroxy groups in ortho/para positions of protocatechuic acid; methoxy and epoxide groups in meta configurations of compound 3-(4-hydroxy-3,5-dimethoxyphenyl)-2-oxiranemethanol. The lack of vital structural activity requirements (i.e 1-en-function on A ring) was attributed to the weak antimicrobial activity (MIQ 50 µg) of the isolated triterpenoids. A number of factors such as poor diffusion, lack of multi-cellular target capacity and proximity necessary for binding of the isolates with microbial cell may have affected the antimicrobial activity.

Keywords:- SAR, RSA, Pathogens, Phytochemicals, A. adianthifolia & P. angolensis.

Acknowledgements:- TET-Fund, FCET Gusau, Zamfara State, Nigeria for the financial support and University of Botswana for providing an enabling environment for research and learning.

References
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3. Mathew, S.; Abraham, T. E.; Zakaria, Z. A. J. of Food Sci. and Tech. 2015, 52, 5790.