PMF@SO3H nanosheet: an efficient novel bifunctional acid–base catalyst for the one-pot synthesis of 14-Aryl-14H-Dibenzo[a,j]xanthenes and evaluation of their antimicrobial activities supported by DFT and molecular docking studies

This study presents the design and synthesis of a highly efficient solid acid catalyst based on mesoporous poly(melamine–formaldehyde) (MPMF) functionalized with 1,4-butanesultone. The composite was characterized using FT-IR, EDX, XRD, and SEM, confirming the incorporation of acidic groups. Its catalytic activity was assessed for synthesizing xanthene derivatives in water at 70 °C, achieving excellent yields in short reaction times. The catalyst showed high stability, maintaining efficiency over five cycles. Additionally, the antibacterial activity of the synthesized xanthene compounds was evaluated against Staphylococcus aureus, E. coli, MRSA, VRE, and Acinetobacter baumannii. Notably, compounds 14-(4-nitrophenyl)-14H-dibenzo[a,j]xanthene (5b) and 14-(4-methoxyphenyl)-14H-dibenzo[a,j]xanthene (8b) exhibited the strongest antibacterial properties, indicating their potential for pharmaceutical applications. Molecular docking study of the tested compounds was performed to investigate the interaction mode of these compounds with the active site of Staphylococcus aureus Gyrase B enzyme. DFT studies on compounds 5b and 8b reveal that 5b is more reactive with a smaller HOMO–LUMO gap and localized electron density, while 8b is more stable with delocalized orbitals. ESP and reactivity descriptors confirm the correlation between charge distribution, hardness, and molecular stability.