Recent investigation on heterocycles with one nitrogen [piperidine, pyridine and quinoline], two nitrogen [1,3,4-thiadiazole and pyrazole] and three nitrogen [1,2,4-triazole]: a review

Heterocycles form by far the largest of classical divisions of organic chemistry and are of immense importance biologically and industrially, and about one half of over six million compounds recorded in chemical abstracts are heterocyclic. The majority of pharmaceuticals and biologically active agrochemicals are heterocyclic while countless additives and modifiers used in industrial applications ranging from cosmetics, reprography, information storage and plastics are heterocyclic in nature. One striking structural feature inherent to heterocycles, which continue to be exploited to great advantage by the drug industry, lies in their ability to manifest substituents around a core scaffold in defined three-dimensional representations. Among the approximately 20 million chemical compounds identified by the end of the second millennium, more than two-thirds are fully or partially aromatic and approximately half are heterocyclic. The presence of heterocycles in all kinds of organic compounds of interest in electronics, biology, optics, pharmacology, material sciences and so on is very well known. Between them, nitrogen-containing heterocyclic compounds have maintained the interest of researchers through decades of historical development of organic synthesis. In the present work, focus on the literature survey of chemical diversity (piperidine 1, pyridine 2, quinoline 3, [1,3,4]-thiadiazole 4, pyrazole 5 and [1,2,4]-triazole 6) in the molecular framework in order to get a complete information regarding pharmacologically interesting compounds of widely different composition. Graphic abstract