Vol. 4, Issue 2, Part A (2018)

Abstract
A hydroxamic acid is a class of organic compounds bearing the functional group RC(O)N(OH)R', with R and R' as organic residues and CO as a carbonyl group. They are amides (RC(O)NHR') wherein the NH center has an OH substitution. Hydroxamic acids are hydrophilic organic compounds that can exhibit keto-iminol tautomerism, and both tautomers may exist as Z (zusammen) or E (Entgegen) diastereomers. They are much weaker acids than the structurally related carboxylic acids RC(=O)OH, and produce hydroxamate ions. The deprotonation could be either from the nitrogen or the oxygen, making them N-acids or O-acids. Hydroxamic acids, having the bidentate functional grouping (I), fulfil the basic requirement of complex formation with metal ions and, therefore, form an important family of chelating agents. Structurally, hydroxamic acids can be represented in their two tautomeric form of type (II) and (III). By substituting the hydrogen atom attached to the nitrogen atom in (II) by alkyl or aryl groups, numerous N-substituted hydroxamic acids of type (IV) can be obtained. The complex formation of hydroxamic acids of type (IV) usually takes place with the replacement of the hydroxylamine hydrogen by the metal ion and ring closure through the carbon oxygen. The most important enzymes that are inhibited by hydroxamic acids are matrix metalloproteinases, TNF-α converting enzyme, angiotensin converting enzyme, lipoxygenase, urease, peptide deformylase, histone deacetylase, procollagen C-proteinase, aggrecanase, and carbonic anhydrase. Thus the hydroxamic acid moiety plays an important role as a pharmacophore to develop drugs against a variety of diseases, such as cancer, cardiovascular diseases, HIV, Alzheimer’s, malaria, allergic diseases, tuberculosis, metal poisoning, iron overload, etc. Besides, hydroxamic acid moiety has also been exploited to develop potential insecticides, antimicrobials, antioxidants, anti-corrosive agents, siderophores, and as a means of flotations of minerals. It is also discussed that hydroxamic acids are also effective nitric oxide (NO) donors, because of which they produce hypotensive effects. Hydroxamic acids find many applications in chemistry and biology and have been the subject of many experimental investigations. Theoretical studies are not as frequent.