Photo-Augmented DHFR Inhibition: <i>N</i> -Methylbenzothiazole Derivatives against Resistant Gram ± Bacteria

The escalating global threat of antimicrobial resistance demands innovative therapeutic strategies that can overcome conventional resistance mechanisms. Here, we report the rational design and development of a novel class of D-π-A conjugated benzothiazole derivatives that synergistically combine dihydrofolate reductase (DHFR) inhibition with photodynamic therapy (PDT) for enhanced antibacterial activity against multidrug-resistant pathogens. Through systematic structure-activity relationship (SAR) studies, we identified compound <b>12</b> as the lead candidate, featuring an unsubstituted benzothiazole core, thiophene π-bridge, and <i>N,N</i>-dimethylaniline donor, which demonstrated superior intrinsic antibacterial activity against both Gram-positive and Gram-negative strains compared to the clinical antibiotics linezolid and vancomycin. Moreover, photodynamic activation of compound <b>12</b> enhanced its antimicrobial efficacy by up to 64-fold through efficient generation of reactive oxygen species (ROS). In a MRSA-infected murine wound model, compound <b>12</b> with PDT treatment achieved complete bacterial eradication and near-complete wound closure (97.36%) at 1/8 the dose of vancomycin, with histological analysis confirming full tissue regeneration. This work establishes a novel therapeutic paradigm that concurrently targets essential bacterial enzymes and employs photochemical mechanisms to effectively overcome antimicrobial resistance.