Isoxazole is a liquid heterocyclic compound C3H3NO isomeric with oxazole and having a penetrating odor like that of pyridine. Isoxazoles belong to an important class of five-membered aromatic heterocycles containing two electronegative heteroatoms, nitrogen and oxygen, in a 1,2-relationship and three regular sp2 carbon atoms. These molecules are found to be key components in various synthetic products in daily use and also present as a pharmacophore essential for biological activity in many drugs and bioactive natural products. In addition, isoxazoles have demonstrated their ability to exhibit hydrogen bond donor/acceptor interactions with a variety of enzymes and receptors.
Oxazolines are five-membered heterocyclic compounds with one double bond. The double bond may be in one of three positions, so there may be three different oxazoline rings. The 2-oxazoline structure is the most common, and 3-oxazoline and 4-oxazoline exist mainly as laboratory research compounds. Oxazolines exist between oxazole and oxazolidine in terms of saturation.