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 They are amides (RC(O)NHR') wherein the NH center has been replaced by an OH. They are often used as metal chelators.
Synthesis and reactions
Hydroxamic acids are prepared usually from esters or acid chlorides or carboxylic acids. For the synthesis of benzohydroxamic acid, the overall equations is:
- C6H5CO2Me + NH2OH → C6H5C(O)NHOH + MeOH
A well-known hydroxamic acid reaction is the Lossen rearrangement.
Coordination chemistry and biochemistry
In the area of coordination chemistry, hydroxamic acids are excellent ligands. They deprotonate to give hydroxamates, which bind to metals ions as bidentate ligands. So high is the affinity of hydroxamates for ferric ions that nature has evolved families of hydroxamic acids to function as iron-binding compounds (siderophores) in bacteria. They dissolve insoluble iron(III) compounds. The resulting complexes are transported into the cell, where the iron is extracted and utilized metabolically.
Other uses and occurrences
Hydroxamic acids are used extensively in floatation of rare earth minerals during the concentration and extraction of ores to be subjected to further processing.
Some hydroxamic acids (e.g. vorinostat, belinostat, panobinostat, and trichostatin A) are HDAC inhibitors with anti-cancer properties. Fosmidomycin is a natural hydroxamic acid inhibitor of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXP reductoisomerase). Hydroxamic acids have also been investigated for reprocessing of irradiated fuel.
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