Design, synthesis, and antibacterial activity study of pyrroloquinazoline diamine derivatives.

To combat antimicrobial resistance (AMR), a novel series of pyrrolo[3,2-f]quinazoline-diamine (PQD) derivatives (5a-5z) featuring a flexible benzyl-oxo-benzyl side chain were designed and synthesised via structural optimisation of lead compound IRS-16. All compounds exhibited potent dihydrofolate reductase (DHFR) inhibition. Compound 5a was most notable, showing exceptional enzymatic inhibition (IC₅₀ = 0.92 nM), surpassing both IRS-16 and trimethoprim. 5a demonstrated broad-spectrum antibacterial activity against Gram-positive (e.g., E. faecalis) and Gram-negative strains (e.g., E. coli), as well as clinical isolates of S. aureus, K. pneumoniae, and uropathogenic E. coli (UPEC), with MIC values as low as 0.5 μg/mL. It displayed rapid bactericidal action, low resistance propensity, and inhibited biofilm formation by >90% at 0.5 μg/mL. Additional mechanisms included disruption of bacterial membrane integrity, causing leakage of cellular contents. These results identify 5a as a promising lead for developing novel, broad-spectrum DHFR inhibitors with a low resistance risk.