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 (1) and millexatin F (2), derived from the tropical medicinal plant Millettia extensa. Through in vitro evaluations, both compounds 1 and 2 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 (1) and millexatin F (2) 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 (2) could interact with phosphatidylethanolamine (PE) and cardiolipin (CL) of cytoplasmic membranes in both Gram-positive and Gram-negative bacteria. Furthermore, millexatin F (2) 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 (1) and millexatin F (2) as lead candidates in the fight against bacterial infections.