Xanthene Derivatives Targeting Bacterial Efflux Pumps, Quorum-Sensing, and Biofilm Formation

The rise of multidrug resistance (MDR) bacteria in nosocomial and health-care institutions is widespread and is currently recognized as a major medical challenge. Mechanisms of bacterial resistance, namely, quorum sensing (QS), biofilm formation, and efflux pumps, have been identified as critical biological processes in MDR bacteria. Following previous reports on the activity of phenothiazines against mechanisms of bacterial resistance, in this work we focus on the synthesis of xanthene derivatives aiming to discover phenothiazine bioisosteres with improved activity. Four compounds were obtained from the conjugation of xanthydrol with sulfonamides and aniline and were fully characterized. Their antibacterial activity was assessed considering their minimum inhibitory concentration (MIC) against Gram-positive and Gram-negative strains, efflux pump inhibition, influence on biofilm formation and quorum-sensing (QS) inhibition. It was observed that the MIC of all the tested compounds was above 64 µg/mL The four 9-xanthenyl derivatives obtained, particularly the xanthene sulfonamide derivatives 3b and 3c, showed promising results on QS inhibition with a reduction of pigment production of 48 and 41 mm, and on biofilm formation with a reduction of 78 and 79%, respectively.