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A hydroxamic acid is a class of
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
s bearing the
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
RC(O)N(OH)R', with R and R' as organic residues and CO as a
carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...
group. They are amides (RC(O)NHR') wherein the NH center has an OH substitution. They are often used as metal
chelator Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
s.


Synthesis and reactions

Hydroxamic acids are usually prepared from either
esters In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...
or
acid chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...
s by a reaction with
hydroxylamine Hydroxylamine is an inorganic compound with the formula . The material is a white crystalline, hygroscopic compound.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–43 ...
salts. For the synthesis of benzohydroxamic acid, the overall equation is: :C6H5CO2Me + NH2OH → C6H5C(O)NHOH + MeOH Hydroxamic acids can also be synthesized from
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s and ''N''-sulfonylhydroxylamine via the Angeli-Rimini reaction. A well-known reaction of hydroxamic acid esters is the
Lossen rearrangement The Lossen rearrangement is the conversion of a hydroxamate ester to an isocyanate. Typically O-acyl, sulfonyl, or phosphoryl O-derivative are employed. The isocyanate can be used further to generate ureas in the presence of amines or generate ...
.


Coordination chemistry and biochemistry

File:Ferrichrome.svg,
Ferrichrome Ferrichrome is a cyclic hexa-peptide that forms a complex with iron atoms. It is a siderophore composed of three glycine and three modified ornithine residues with hydroxamate groups N(OH)C(=O)C- The 6 oxygen atoms from the three hydroxamate gr ...
File:Deferoxamine-2D-skeletal.png ,
Deferoxamine Deferoxamine (DFOA), also known as desferrioxamine and sold under the brand name Desferal, is a medication that binds iron and aluminium. It is specifically used in iron overdose, hemochromatosis either due to multiple blood transfusions or an un ...
File:Rhodotorulic acid.svg,
Rhodotorulic acid Rhodotorulic acid is the smallest of the 2,5-diketopiperazine family of hydroxamate siderophores which are high-affinity chelating agents for ferric iron, produced by bacterial and fungal phytopathogens for scavenging iron from the environment. I ...
File:Fe(hydroxamate)3.svg, Fe(III) complex of triacetylfusarinine Many hydroxamates have been isolated from natural sources. They appear to function as ligands, usually for iron. They form by deprotonation of hydroxamic acids, Hydroxamates bind to metals ions as
bidentate ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s, forming five-membered MO2CN rings. Nature has evolved families of hydroxamic acids to function as iron-binding compounds (
siderophore Siderophores (Greek: "iron carrier") are small, high-affinity iron- chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is n ...
s) in bacteria. They extract iron(III) from otherwise insoluble sources (rust, minerals, etc.). The resulting complexes are transported into the cell, where the iron is extracted and utilized metabolically. Ligands derived from hydroxamic acid and thiohydroxamic acid also form strong complexes with lead(II).


Other uses and occurrences

Hydroxamic acids are used extensively in flotation of rare earth minerals during the concentration and extraction of ores to be subjected to further processing. Some hydroxamic acids (e.g.
vorinostat Vorinostat (rINN) also known as Suberoylanilide hydroxamic acid ( suberoyl+anilide+ hydroxamic acid abbreviated as SAHA) is a member of a larger class of compounds that inhibit histone deacetylases (HDAC). Histone deacetylase inhibitors (HDI) ...
,
belinostat Belinostat (trade name Beleodaq, previously known as PXD101) is a histone deacetylase inhibitor drug developed by TopoTarget for the treatment of hematological malignancies and solid tumors. It was approved in July 2014 by the US FDA to treat pe ...
,
panobinostat Panobinostat, sold under the brand name Farydak, is a medication used for the treatment of multiple myeloma. It is a hydroxamic acid and acts as a non-selective histone deacetylase inhibitor (pan-HDAC inhibitor).trichostatin A Trichostatin A (TSA) is an organic compound that serves as an antifungal antibiotic and selectively inhibits the class I and II mammalian histone deacetylase (HDAC) families of enzymes, but not class III HDACs (i.e., sirtuins). However, there are ...
) are
HDAC inhibitor Histone deacetylase inhibitors (HDAC inhibitors, HDACi, HDIs) are chemical compounds that inhibit histone deacetylases. HDIs have a long history of use in psychiatry and neurology as mood stabilizers and anti-epileptics. More recently they are be ...
s with anti-cancer properties.
Fosmidomycin Fosmidomycin is an antibiotic that was originally isolated from culture broths of bacteria of the genus '' Streptomyces''. It specifically inhibits DXP reductoisomerase, a key enzyme in the non-mevalonate pathway of isoprenoid biosynthesis. It ...
is a natural hydroxamic acid inhibitor of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (
DXP reductoisomerase DXP reductoisomerase (1-deoxy-D-xylulose 5-phosphate reductoisomerase or DXR) is an enzyme that interconverts 1-deoxy-D-xylulose 5-phosphate (DXP) and 2-C-methyl-D-erythritol 4-phosphate (MEP). Image:DOXP.png, 1-Deoxy-D-xylulose 5-phosphate ...
). Hydroxamic acids have also been investigated for reprocessing of irradiated fuel.


References


Further reading

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