Racemosol Derivatives and Other Metabolites from Bauhinia malabarica Bark with Antibacterial Activity

Racemosol, a natural phenolic compound, is known for its antimicrobial potential, yet experimental studies remain limited. In this study, two new racemosol derivatives (4 and 5) and four known compounds (1–3, 6) were isolated from the bark of Bauhinia malabarica and structurally elucidated using spectroscopic analyses. Most of isolated compounds exhibited notable activity against Gram-positive bacteria, including Staphylococcus aureus, Bacillus subtilis, and Listeria monocytogenes, while showing limited effects on Gram-negative strains. Racemosol (1) and its derivatives (2, 4, and 6) displayed potent antibacterial activity with MIC values of 0.156–0.625 µg/µL and bactericidal properties confirmed by comparable MBCs. Compound 6 exhibited the highest potency, indicating that specific structural modifications enhance activity. These findings provide new insights into the structure activity relationships of racemosol derivatives and highlight B. malabarica as a promising natural source of phenolic antibacterial agents.