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.
Oxirane is a three-membered ring compound consisting of one oxygen atom and two carbon atoms. Oxirane is present in natural products such as cryptocin, which has anticancer properties, and azidomycin, trienone, and epoxidomycin, which have shown activity against drug-resistant leukemias and AIDS-related lymphomas. Other oxirane containing bioactive molecules have anti-inflammatory, immunosuppressive, and antitumor activities. Oxiranes are a strained ring susceptible to various nucleophilic, ring-opening or rearrangement reactions, so they are considered to be one of the most important intermediates in organic synthesis.
Oxazoles are heterocyclic aromatic compounds containing one oxygen atom and one nitrogen atom, separated by a carbon atom. The presence of two heteroatoms (oxygen and nitrogen) provides possible interactions (hydrogen, hydrophobic, van der Waals or dipole bonds) with a wide range of receptors and enzymes. Oxazole rings are valuable heterocyclic scaffolds for the design of novel therapeutics with anticancer, antiviral, antibacterial, anti-inflammatory, neuroprotective, antidiabetic, and antidepressant properties due to their wide range of targets and biological activities.