Total Synthesis of Auriculatin and Millexatin F and Discovery of Their Antibacterial Mechanism

The emergence of multidrug-resistant (MDR) bacteria necessitates the urgent development of novel antibacterial agents. This study reported the first total synthesis of two antibacterial isoflavones, auriculatin (<b>1</b>) and millexatin F (<b>2</b>), derived from the tropical medicinal plant <i>Millettia extensa</i>. Through <i>in vitro</i> evaluations, both compounds <b>1</b> and <b>2</b> possessed significant antibacterial activities (MICs = 0.5-4 μg/mL) and rapid bactericidal properties against Gram-positive bacteria, along with high safety for mammalian cells. Mechanistic studies revealed that auriculatin (<b>1</b>) and millexatin F (<b>2</b>) interact with bacterial cell membranes, inducing alterations in bacterial morphology and membrane permeability and inducing a rise in the leakage of intracellular DNA and proteins, thereby leading to bacterial death. In addition, our studies indicated that millexatin F (<b>2</b>) could interact with phosphatidylethanolamine (PE) and cardiolipin (CL) of cytoplasmic membranes in both Gram-positive and Gram-negative bacteria. Furthermore, millexatin F (<b>2</b>) showed increased efficacy against Gram-negative bacteria when combined with a permeabilizer (polymyxin B nonapeptide), indicating potential for broader application. These findings underscore the therapeutic promise of auriculatin (<b>1</b>) and millexatin F (<b>2</b>) as lead candidates in the fight against bacterial infections.