Hydroxylamino acids

Reduction—Continued of a hydroxylamino acid to an amino acid by hydroxylamine, 33, 26 of a nitro compound to an amine, S3,9 of a nitro compound to an azo compound, 22, 28... 

Figure 9.34 Total hydrolyzable amino acid (THAA) concentrations (mg L-1) during (a) oxic and (b) anoxic decay of the dinoflagellate P minimum over different time periods. Hydroxylamino acids not shown, and nonprotein amino acids = /3-alanine and y-aminobutync acid. (Modified from Nguyen and Harvey, 1997.)...

The first simple 5(2/f)-oxazolones were the trifluoromethyl derivatives obtained by treating a-amino acids with trifluoroacetic anhydride (equation 156). A general synthesis of 2,2-disubstituted 5(2/f)-oxazolones is the condensation of a- (hydroxylamino) acids with ketones (equation 157) (80S55). The dehydrogenation of 2,2-bis(trifluoromethyl)-5-oxazolidinones affords bis(trifluoromethyl) derivatives (equation 158) (79LA1547). 

The reaction of a lithium ester enolate (146) with a nitrone (147) to yield a fi-hydroxylamino acid ester (149) has been recently investigated by Domingo, Merino and coworkers, using DFT (B3LYP/6-31G ) methods, to gain insight on the molecular mechanism. The proposed transition structure (148) shown in equation 42 derives from attack of the most nucleophilic center of enolate 146 on the most electrophilic center of... 

The action of phosgene or thionyl chloride on the )V-(benzyl-oxycarbonyl)amino-acids PhCH202CNHCHRC02H (R == PhCH2 or Pr ) yields 2-oxazolin-5-ones (522), contrary to a previous report/ Numerous 3-oxazolin-5-ones (523 R , R R = alkyl or Ph) have been prepared from hydroxylamino-acids H0NHCHR C02H and ketones R COR. The revised structure (524) has been established by X-ray diffraction for the product of the reaction of ethyl diazoacetate with di-isopropylcarbodi-imide, catalysed by salts of transition metals. Treatment of the diazomethylphosphoryl compound (Me0)2P(0)CHN2 with aroyl isocyanates affords the 2-oxazolin-4-ones (525)/ ... 

T. Polonski and A. Chimiak, Oxydation of Amino Acid Esters into N-Hydroxylamino Acid Derivatives, Tetrahedron Lett. 1974, 2453-2456. 

Spenser, I.D., and A. Ahmad a-Amino Acids and a-Keto Acid Oximes from a-Hydroxylamino Acids a New Disproportionation Reaction. Proc. Chem. Soc. (London) 1961, 375. 

Neither the oxygenation of an amino acid to yield a hydroxylamino acid nor the acylation of a hydroxylamino acid to yield a hydroxamic acid has been previously described, and the isolation of the enzymes responsible for these novel reactions is a challenging problem. Several attempts have already been made in our laboratory with cell-free extracts of P, aurantio-violaceum to find enzymic activity that would carry out the formylation of N-hydroxyglycine to yield hadacidin. The rapid incorporation of formate into hadacidin by intact myceUa would indicate that this activity must be very high in vivo, but thus far these experiments have not met with success. If Neiland s hypothesis that hydroxa-mates are involved in the transport of iron across the cell membrane is correct, the enzymes responsible for hadacidin synthesis might not be found in the soluble portion of the cell-free extract, but instead would be closely etssociated with insoluble components found in the cell debris after the myceha are mechanically disrupted. 

Leucine is known to be a precursor of neoaspergillic acid and pulcherriminic acid, and MacDonald s results would seem to rule out a role of the N-hydroxyamino acids as intermediates in the biosynthesis of these hydroxamates, although direct experiments using the hydroxylamino acids as substrates would be desirable. In the aspergillic acid family, it thus appears that the amino acid nitrogen undergoes substitution by carbon prior to its oxidation (oxygenation ). 

Finally, in view of the finding that molecular oxygen is involved in the conversion of amino acids to hydroxylamino acids, at least in the case of hadacidin biosynthesis, it might be appropriate to speculate on the role of iron in inhibiting... 

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