1,2,5-Oxadiazole is a five-membered, heteroaromatic, planar heterocycle comprised of one oxygen atom with two vicinal nitrogen atoms (N-O-N) and two carbon atoms at the 3- and 4-positions of the ring. It is a π-excessive heterocycle also referred to by its trivial name furazan and corresponding 2-N-oxide as furoxan. The ionization energy of oxadiazole is 11.79 eV and the dipole moment is 3.38 D greater than isoxazole. The π electron density of the nitrogen atom is greater than the oxygen and carbon atoms as depicted in the following scheme.
The parent 1,2,5-oxadiazole is a colorless liquid with an mp of ?28°C and a bp of 98°C, soluble in water and stable at room temperature. Its density is 1.168 g/cm.3
1,2,5-Oxadiazole derivatives are found to be potent inhibitors of indoleamine 2,3-dioxygenase and are useful for the treatment of cancer and other disorders. They are also useful as a new class of SENP2 inhibitors and can be used for the development of novel therapeutic agents for various diseases targeting SENPs. 1,2,5-Oxadiazole-2-oxides are used as a source of NO in biological studies. 4-Amino-1,2,5-oxadiazole-2-oxide-3-carboxylic acid and azo derivatives have been studied for their vasodilating properties.
