The uses of 1,2,4-oxadiazoles include those as agonists at muscarinic receptors, 5-hydroxytryptamine (5-HT) receptor antagonists, benzodiazepine receptor agonists, potent antagonists of the (serotonin) 5-HT1B/D receptors, muscarinic receptor ‘superagonists’, selective inhibitors of human neutrophil elastase, and as active and selective A2B adenosine receptor antagonists. Much interest stems from the use of the fully conjugated 1,2,4-oxadiazole as a hydrolysis resistant ester or amide bioisostere and peptidomimetic. Amongst the non- fully conjugated systems, the soluble guanylyl cyclase inhibitor ODQ is a potent and selective inhibitor of nitric oxide-sensitive guanylyl cyclase and (S)-quisqualic acid is a neuroexcitatory naturally occurring amino acid. Synthetic approaches to the fully conjugated system are dominated by the conversion of a carboxylic acid into an activated derivative, followed by O-acylation of an amidoxime fragment and ring closure. A second popular route is 1,3-dipolar cycloaddition of a nitrile oxide to a nitrile. The reaction of an amidoxime with a carbonyl or the 1,3-dipolar cycloaddition of a nitrile oxide to an imine, or of a nitrone to a nitrile, provides the major routes to the nonconjugated dihydro-1,2,4-oxadiazoles. The reactions of fully conjugated 1,2,4-oxadiazoles and their nonconjugated analogues are detailed together with an in-depth analysis of their structural, theoretical, and thermodynamic properties.
Original languageEnglish
Title of host publicationComprehensive Heterocyclic Chemistry III
EditorsAlan R. Katritzky, Christopher A. Ramsden, Richard J.K. Taylor
PublisherElsevier Ltd
Number of pages72
ISBN (Print)9780080449920
Publication statusPublished - 1 Dec 2008


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