Antimicrobial Evaluation of Sulfonamides after Coupling with Thienopyrimidine Coplanar Structure

This work describes the design and synthesis of three series of hybrids of thienopyrimidines and sulfonamides. Dihydrofolate reductase enzyme was selected as a target for the in-silico screening of the synthesized thienopyrimidine-sulfonamide hybrid as an antibacterial, while squalene epoxidase was selected as an antifungal target protein. All screened compounds showed promising binding affinity ranges, with perfect fitting not exceeding 1.9 Å. The synthesized compounds were tested for their antimicrobial activity using agar well diffusion and minimum inhibitory concentration tests against six bacterial strains in addition to two Candida strains. Compounds 8iii and 12ii showed varying degrees of inhibition against Staphylococcus aureus and Escherichia coli bacterial strains, whereas the best antifungal activity against Candida was displayed by compound 8iii. Compound 12ii, the cyclohexathienopyrimidine coupled with sulfadiazine at position 3, has the best antibacterial activity, which is consistent with molecular docking results at the active site of the oxidoreductase protein. Interestingly, compound 12ii also has the highest docking binding energy at the antifungal squalene epoxidase active site. Investigating the physicochemical properties of the synthesized hybrids revealed their high tolerability with cell membranes, and moderate to poor oral bioavailability, and that all are drug-like candidates, among which 4i, the cyclohexathieno[2,3-d] pyrimidine core with sulphaguanidine incorporated at position 4, recorded the best score (1.58).