Anti-infective activity, phytochemistry and cytotoxicity of Dalbergia Melanoxylon Guill. & Perr and Ormocarpum Sennoides ssp. Zanzibaricum Brenan & J.B. Gillett

Abstract

Infectious diseases account for 90% of the disease burden worldwide with a significant rampage being felt in developing countries. This is coupled by the widespread antibiotic resistance to available conventional drugs. Infectious agents have been reported to raise the risk of human cancer which is a major cause of mortality worldwide. The aim of this study was to investigate Dalbergia melanoxylon Guill. & Perr and Ormocarpum sennoides subsp. zanzibaricum Brenan & J.B. Gillett as potential anti-infective and anticancer agents. Extraction of root bark of D. melanoxylon was done using CH2Cl2/MeOH (1:1) while O. sennoides subsp. zanzibaricum was extracted using 80% methanol and partionioned to obtain n-hexane, ethylacetate, n-butanol and water extracts. The structures and absolute configuration of the isolated compounds were elucidated by Mass spectrometry, Nuclear magnetic resonance and Electronic circular dichroism spectroscopy. The antibacterial activity of the crude extract and the isolated compounds against Bacillus subtilis and Aliivibrio fischeri was determined in a turbidimetric assay. The pure compounds were subjected to a panel of human pathogenic bacteria (Enterococcus faecalis, Escherichia coli, Mycobacterium vaccae, Staphylococcus aureus, methicillin resistant Staphylococcus aureus and Pseudomonas aeruginosa using agar diffusion assay. The crude extracts were tested for antifungal activity against Phytophthora infestans, Botrytis cinerea, and Septoria tritici using turbidimetric assay. The pure compounds were subjected to further antifungal testing against human pathogenic fungi (Sporoidiobolus salmonicolor, Candida albicans and Penicillium chrysogenum) using agar diffusion assay. The crude extracts of O. sennoides subsp. zanzibaricum and D. melanoxylon (500 μg/ml) were tested for anthelmintic activity using Caenorhabditis elegans. The cytotoxicity (CC50) of the crude extracts against the human prostate cancer (PC-3) and colon adenocarcinoma (HT-29) was performed using colorimetric cell viability assays. The cytotoxicity assay against HeLa cells was performed on the most promising active pure compound using the methylene blue assay.Phytochemical investigation of root and root bark of O. sennoides subsp. zanzibaricum and D. melanoxylon resulted in the isolation of twenty compounds (1-20), of which seven are new. The root bark of D. melanoxylon yielded six previously undescribed prenylated isoflavanones (1-6), alongside isoflavanoids (7-10), neoflavones (11-13) and alkyl hydroxycinnamates (14). A new biflavonoid, trime-chamaejasmin (15) alongside two known biflavonoids (16-17), bi-4-phenyldihydrocoumarin (18), isoflavan (19), triterpenoid (20) were also isolated from the roots of O. sennoides subsp. zanzibaricum. The crude extracts at 50 and 500 μg/mL exhibited promising antibacterial activity against Bacillus subtilis. Sophoraisoflavanone A (10) caused inhibition against both B. subtilis and Aliivibrio fischeri assays at 99% at 100 µM. Kenusanone H (7) and (3R)-tomentosanol B (9) exhibited promising antibacterial activity against MRSA and M. vaccae showing minimum inhibitory concentrations between 0.8 and 6.2 µg/mL. Both crude extracts showed promising antifungal activity against all phytopathogens at 125 µg/mL. Kenusanone H (7) at 42 µg/mL showed very promising activity against S. tritici (74%) and B. cinerea (99%). At low 0.05 μg/mL, both crude extracts showed no cytotoxic effect against PC-3 and HT-29 cells. Kenusanone H (7) was highly cytotoxic against HeLa cells with CC50 of 1.8 ± 1.4 µg/mL (4.2 µM). The crude extracts of both O. sennoides subsp. zanzibaricum and D. melanoxylon are not toxic in general but show selective antibacterial and antifungal activities. Kenusanone H (7) proved to be a lead drug candidate as an antibacterial, antifungal and cytotoxic compound.