Heterocyclic compounds are cyclic compounds that have atoms of at least two different elements as members of their ring(s) . They are a major class of organic chemical compounds characterized by the fact that some or all of the atoms in their molecules are joined in rings. Examples of heterocyclic compounds include nucleic acids, the majority of drugs, most biomass, and many natural and synthetic dyes. More than half of known compounds are heterocycles, and 59% of US FDA-approved drugs contain nitrogen heterocycles.
Heterocyclic compounds can be classified based on their electronic structure. The two main types are aliphatic heterocyclic compounds and aromatic heterocyclic compounds. Aliphatic heterocyclic compounds are those cyclic heterocycles that do not contain any double bond, while aromatic heterocyclic compounds contain at least one double bond in the ring. Examples of heterocyclic compounds with more than one heteroatom include pyrazole, imidazole, oxazole, thiazole, triazole, and tetrazole. Six-membered heterocyclic compounds are derived from benzene by replacing one of the carbon atoms with a heteroatom having a lone pair of electrons.
Heterocyclic compounds are used in a variety of applications, including drugs, pesticides, dyes, and plastics. They are also found in many naturally occurring compounds, such as mono and polysaccharides, and the four DNA bases.
