A Review on the Synthesis and Biological Evaluation of N-containing Heterocyclic Derivatives

Abstract: Nitrogen-containing heterocyclic derivatives constitute a vital class of bioactive compounds, with approximately 75% of FDA-approved small-molecule drugs incorporating at least one N-heterocyclic core. This review covers the most recently synthesized biologically active N-heterocyclic compounds evaluated for their anti-fungal, anti-inflammatory, anti-bacterial, antioxidant, anticonvulsant, antiallergic, herbicidal, and anticancer properties, emphasizing traditional and modern synthetic methodologies, including metal-catalyzed, multicomponent, and green chemistry approaches. The structure-activity relationships (SAR) of these derivatives are analyzed, elucidating their interactions with biological targets. Cyclization reactions of amines and carbonyl-containing compounds, multicomponent reactions (MCRs), and Metal-catalyzed coupling reactions (Suzuki, Sonogashira, and Buchwald-Hartwig reactions) have emerged as efficient synthetic strategies, providing a rapid approach for constructing complex scaffolds in a single step and functionalizing for the synthesis of a variety of nitrogen-containing heterocycles. Triazole and imidazole derivatives have been found to exhibit antibacterial and antifungal activities. Quinolines, indoles, and pyrazoles have shown notable cytotoxicity against various human cancer cell lines. Pyridine and pyrimidine derivatives have exhibited significant inhibitory action against HIV and have been identified as potential antiviral agents. Heterocycles bearing halogen substituents and fused aromatic systems showed improved activity due to enhanced cell permeability and receptor binding affinity. The analysis of reported methods reveals that greener approaches-such as solvent-free synthesis, microwave-assisted reactions, and the use of benign catalysts -are employed in biological evaluation and structure-activity relationship (SAR) studies to modulate biological targets through hydrogen bonding, π-π stacking, and coordination with metal ions. However, despite the promising results, there is a lack of in vivo and toxicity studies for many of the newly synthesized derivatives. The discussion also identifies challenges such as poor aqueous solubility and metabolic instability in some classes of N-heterocycles, which may limit their drug-like potential. By summarizing recent developments in synthesis and biological assessment, this review aims to guide future research in the design of novel bioactive N-heterocyclic compounds with enhanced efficacy against various diseases.