Recent advances in the synthesis, structural diversification, and biological evaluation of sulfamethoxazole derivatives.

Sulfamethoxazole is a clinically important sulfonamide antibiotic that remains a valuable pharmacophore in medicinal chemistry due to its established antibacterial activity and structural versatility. However, the emergence of antimicrobial resistance and limitations related to solubility, pharmacokinetics, and safety have encouraged extensive structural modification of the sulfamethoxazole scaffold. This review summarizes recent advances in the synthesis, structural diversification, and biological evaluation of sulfamethoxazole derivatives, with emphasis on developments reported during the last five years. Major synthetic approaches discussed include conventional sulfonamide-bond formation, greener synthetic protocols, metal complexation, Schiff base formation, nucleophilic substitution, amidation, cyanoacetylation, chloroacetylation, diazotization, heterocyclic annulation, and hybridization with other pharmacologically active scaffolds. Attention is given to how modification of the aromatic amino group, sulfonamide moiety, and isoxazole ring influences physicochemical properties and biological performance. The review also highlights sulfamethoxazole-based metal complexes, heterocyclic hybrids, prodrug-like derivatives, and nanocarrier-based systems as promising strategies to enhance antimicrobial potency and broaden biological applications, including anticancer, antioxidant, anti-inflammatory, enzyme-inhibitory, and antibiofilm activities. Overall, this review provides an integrated overview of the relationship between synthetic design, structural features, and biological activity, offering useful guidance for the future development of sulfamethoxazole-based therapeutic candidates.