Bioactivity guided extraction of PDHC [3,3’-(propane-2,2-diyl)bis(3,4,5,6,7,8- hexahydro-1h-isochromene)]: A Novel antibacterial compound from an ornamental plant Polyalthia longifolia

Abstract

Objective: The objective of the study was to determine and compare the antibacterial effect of different ornamental plants and to isolate the effective bioactive compound with antibacterial activity from Polyalthia longifolia. Methods: Petroleum ether and methanol extracts of Bougainvillea glabra, Polyalthia longifolia, Ixora coccinea Linn. ,Plumeria rubra and Euphorbia milli leaves were investigated for antimicrobial activity by performing agar well difusion method. The plant extract with the highest antibacterial activity was selected and further used for the isolation of antibacterial compounds. In silico docking studies and in vitro antibacterial assay was performed to analyze the biological activity of pure compound. Results: The highest antibacterial activity was found in the pet ether of Polyalthia longifolia against all the tested bacterial strains and the extract was further selected for compound separation. A novel compound 3,3’-(propane-2,2-diyl)bis(3,4,5,6,7,8-hexahydro-1H-isochromene) (PHDC) with a molecular weight of 316.35 g/mol and molecular formula C21H32O2 was identified from Polyalthia longifolia by using spectroscopic studies. In the in vitro antibacterial assay, PHDC demonstrated significant antibacterial showed against Protease mirabilis. In silico docking studies revealed that PHDC showed antibacterial activity by inhibiting tRNA Synthetase (IleRS). PHDC exhibited the lowest binding energy of - 8.7Kcal/Mol for Isoleucyl tRNA Synthetase (IleRS), the protein responsible for protein synthesis. Conclusion: The emergence of multiple antibiotics resistant microbes has become huge nowadays and the infections caused by these resistant microbes cannot be treated with antibiotics. PHDC is a novel compound extracted from Polyalthia longifolia showed significant antibacterial effect and we suggest that the compound can be further used as lead molecules to overcome the infections caused by antibiotic resistant bacteria.