Hydroxylamino Derivatives

In spite of the usefulness of the Beirut reaction, mechanistically it is not well understood. It has been suggested that the first step involves the nucleophilic attack by the enolate or the enamine at N-3 of the benzofuroxan to yield an intermediate iV-oxide (Scheme 50) which subsequently undergoes tautomerism to an hydroxylamino derivative. This intermediate then cyclizes to the dihydroquinoxaline 1,4-dioxide. This suggestion has not been proven, and indeed there is evidence that benzofuroxan is in equilibrium with 1,2-dinitrosobenzene... 

Carbon-Oxygen Bond Formation The cathodic reduction of some nitrocarhonyl compounds in aqueous acidic medium gives the hydroxylamino derivatives that can undergo a ring-closure reaction affording anthrandic compounds or isoxazolones [102-104] (Schemes 70 and 71). 

Nitro compounds are easily reduced, catalytically or chemically, to amino compounds. Incomplete reduction can lead to a hydroxylamino derivative or to binuclear azo, azoxy and hydrazo compouds, e.g. (760) — (759), (761). A nitro group can be reduced in the presence of an iV-oxide group, e.g. (755) - (752). 

F. Peri, P. Dumy, and M. Mutter, Chemo- and stereoselective glycosilation of hydroxylamino derivatives A versatile approach to glycoconjugates, Tetrahedron, 54 (1998) 12269-12278. 

Reduction of a-nitro-j6-hydroxybutyric acid to D,L-threonine [65] and similar reactions [33,66] have been investigated for the preparation of amino acids. The reduction to amine passes predominantly through the hydroxylamino derivative and only to a smaller degree through the oxime. 

Simple alkyl or aryl esters Alkyl esters containing an amino or amido group, or another functionality (Acyloxy)methyl or (acyloxy)ethyl esters Esters of diacylaminopropan-2-ols N,N-Dialkyl hydroxylamino derivatives Amides of amino acids... 

Naumov AV et al., Transformation of 2,4,6-trinitrotoluene into toxic hydroxylamino derivatives by Lactobacilli, Microbiology, 68, 46, 1999. 

Reductive biotransformations of several compounds such as polyhalogenated, keto, nitro and azo derivatives, are catalysed by a variety of enzymes which differ according to the substrates and the species. The liver cytochrome P-450-dependent drug metabolizing system is capable of reducing Af-oxide, nitro and azo bonds, whereas the cytosolic nitrobenzene reductase activity is mainly due to cytochrome P-450 reductase, which transforms nitrobenzene into its hydroxylamino derivative. NADPH cytochrome c reductase is also able to catalyse the reduction of nitro compounds. These metabolic conversions may also be brought about by gastrointestinal anaerobic bacteria. 

Cytosine arabinoside is enzymatically deaminated in the liver. The resulting product, uracil arabinoside, no longer possesses antileukaemia or antiviral activity [291, 292, 340, 341]. A variety of cytosine derivatives have been studied as deaminase inhibitors. The most active of these was a 4-hydroxylamino derivative, iV -hydroxy-5-methyl-2 -deoxycytidine [342]. 

Nitroaromatic compounds can be initially reduced to aniline derivatives via the intermediary formation of nitroso- and hydroxylamino derivatives (Fig. 3). Subsequently, the amines can be reductively deaminated, yielding benzene derivatives and ammonium (5,6). Several bacteria are only capable of partial degradation of nitroaromatic compounds and either use the released ammonium as a nitrogen source for growth without further degradation of the aromatic ring (5, 6, 45), or use the nitroaromatic compound only as an electron acceptor under anaerobic conditions (2, 3, 12, 34, 38, 47). In the latter case, the amine produced by the reduction of the nitroaromatic compound is not further converted. 

Cartwright and Cain (11) studied reduction of the nitro group of nitrobenzoic acids by enzymes in cell-free extracts of Nocardia erythropolis. Detection of the nitroso and hydroxylamino derivatives of nitrobenzoate indicated that they were intermediates in reduction to aminobenzoate. This study attributed nitroreductase activity to a single soluble metalloflavoprotein that catalyzes the entire reduction from the nitro to the amino group. Glucose grown cells reduced nitrobenzoate to aminobenzoate, which suggested that the reaction was not catalyzed by a specific inducible nitroreductase. 

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