A-Iminocarboxylic acids

Reaction of 6-aminopyrimidines with 2 mol of a-ketoaldehyde in aqueous medium gave rise to the zwitterionic a-iminocarboxylic acids thus, 214 with methylglyoxal gave the pyrimido[l,6- ]pyrimidin-2-carboxylic acid 215 (Equation 26) <2005W02005/039589>. 

Potassium/tert-butanol Cyclic a-iminocarboxylic acids from a-cfalorolactams... 

B. Addition Reactions to a-Acylimino- and a-Iminocarboxylic Acid Derivatives 297... 

Shin was unable to observe enamino-imino tautomerism in the case of dehydrovaline compounds (253, 373). E. Ohler and U. Schmidt (287, 350) were able to convert a-iminocarboxylic acid esters into a-enaminocarboxylic acid esters (42) by preparing the hydrochlorides of the former, which slowly rearranged into the hydrochlorides of the latter. This reaction is the simplest means of preparing a-enaminocarboxyhc acid esters, as the a-iminocarboxylic acid esters obtained by N-chlorina-tion/dehydrochlorination of amino acid esters can be rearranged directly, without intermediate purification. 

N-Chlorination/dehydrochlorination of amino acid esters 310) is the simplest route to a-iminocarboxylic acid esters. With the exception of the leucine derivative, which was obtained as a tautomeric mixture, no enamine could be detected in the products by NMR spectroscopy. Phenylalanine ester yielded the enaminoacid ester exclusively. 

By addition of pyruvoyl chloride to a-iminocarboxylic acid derivatives 295a, 295b, 311). 

Sodium tert-butoxide a-Iminocarboxylic acid amides and a-hydrazinocarboxylic acid esters from 1,2-diazetidinones... 

Preparation of a-amino acids by catalytic hydrogenation of ot-oxo acids in aqueous ammonia in the presence of platinum, palladium or Raney nickel catalysts, probably via an unstable iminocarboxylate ion intermediate ... 

Figure 5 (a) 4-Hydroxyproline selector (138) (b) Iminocarboxylic acid selector (166) (c) Histidine selector (168) (d) Poly-L-phenylalanine amide selector (165). 

Common proteinogenic amino acids may show some toxic effects in animals, for example L-tryptophan and l-3,4-dihydroxyphenylalanine (dopa). In plants about 700 aminocar-boxylic and iminocarboxylic acids occur (see Section 2.2.1.2), which do not occur in proteins and are classified as secondary metabolites. Many of these compounds are structurally similar to the basic (proteinogenic) amino acids and their toxicity may be manifested in a variety of symptoms. The mechanism of toxicity is usually due to one of the following effects ... 

Dehydroamino Acids, a-Hydroxy-a-amino Acids and a-Mercapto-a-amino Acids 281 E. CK-Iminocarboxylic Acid Derivatives... 

Most syntheses of iminocarboxylic acid derivatives start from a-keto acids or a-amino acids. Thus Appel and Hauss 12) described the formation of a-iminopropionic acid ester by treatment of pyruvic acid ester with triphenylphosphine imine. This product was however not isolated, but hydrogenated directly to the corresponding alanine ester. 

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