Discovery of new bioactive secondary metabolites from the stem bark of oroxylum indicum: isolation, structural identification, antimicrobial and cytotoxicity assessment

Abstract

This study aimed to identify potent antimicrobial compounds from Ayurvedic plant Oroxylum indicum. Phytochemical examination of its stem bark led to the isolation of 29 chemical constituents, including five compounds for the first time from this genus: Chrysophanol (12), Ipriflavone (15), Pinoresinol diglucopyranoside (22), Quercetin 3-O-β-D-glucofuranoside (28), and 5-hydroxy-3,7,8,3′,4′-pentamethoxyflavone (29). Notably, compound 28 was a unique flavonoid bearing a β-D-glucofuranoside moiety, very rare in this class. Structural elucidation of the compounds (1–29) was achieved using 1D/2D NMR and HRESI-MS spectrometry. Antimicrobial susceptibility analysis identified two potent compounds (28 and 29) exhibiting MIC and MBC in the range of 0.09 µM to 1.5 µM and 0.7 µM to 6.25 µM against the tested bacterial pathogens, respectively. Further, bactericidal potential of the two identified hit were validated by time-kill kinetics studies. Cytotoxicity assessment in mammalian macrophage cell lines (RAW 264.7 and J774A.1) and hemolysis assays represented an acceptable cytocompatibility profile of these two molecules within the tested concentration range. These findings highlight molecules (28 and 29) as promising compounds for the development of novel antibacterial against Gram-positive and Gram-negative pathogens.