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 (<b>4</b> and <b>5</b>) and four known compounds (<b>1</b>-<b>3</b>, <b>6</b>) were isolated from the bark of <i>Bauhinia malabarica</i> and structurally elucidated using spectroscopic analyses. Most of isolated compounds exhibited notable activity against Gram-positive bacteria, including <i>Staphylococcus aureus</i>, <i>Bacillus subtilis</i>, and <i>Listeria monocytogenes</i>, while showing limited effects on Gram-negative strains. Racemosol (<b>1</b>) and its derivatives (<b>2</b>, <b>4</b>, and <b>6</b>) displayed potent antibacterial activity with MIC values of 0.156-0.625 µg/µL and bactericidal properties confirmed by comparable MBCs. Compound <b>6</b> 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 <i>B. malabarica</i> as a promising natural source of phenolic antibacterial agents.