imidazopyridine

Imidazopyridine is a class of bicyclic nitrogen-containing heteroaromatic compounds in which an imidazole ring is fused to a pyridine ring. The fused system yields several isomers depending on the fusion pattern; the most common core is imidazo[1,2-a]pyridine, with other arrangements such as imidazo[1,2-c]pyridine reported.

Physicochemical properties: The structure is planar and contains two nitrogen atoms (one in each ring) that can act as hydrogen-bond acceptors. The basicity of the nitrogens is reduced by fusion, but substituents can tune pKa and lipophilicity. The fused ring system serves as a versatile scaffold for diversification.

Occurrence and applications: Imidazopyridines appear in medicinal chemistry as core scaffolds for a variety of biologically active compounds. Notably, zolpidem, a hypnotic, contains an imidazopyridine core and is used clinically as a sedative-hypnotic. Derivatives have been explored for CNS activity, antimicrobial and anticancer properties, among others. The motif also appears in coordination chemistry as ligands for metal centers.

Synthesis: Multiple routes exist. General approaches include cyclocondensation of 2-aminopyridines with 1,2-dicarbonyl compounds or α-haloketones, followed by cyclization to form the imidazole ring fused to the pyridine. Other methods assemble the two rings stepwise or via oxidative ring closure, enabling substitution at various positions of the fused system.

Safety and handling: As with many heteroaromatics, handling and purification depend on the specific derivative. They are typically handled under standard laboratory organic-chemistry practices.