Benzoylamino acids

The azlactones are first hydrolyzed with alkali to the A-benzoylamino acid and thence to 32 using an HBr-acetic acid mixture. 

Ih this latter process an a/3-unsaturated a-benzoylamino-acid is formed and is converted into the a-amino-acid by hydrogenation and subsequent removal of the benzoyl group by hydrolysis. 

Milewska and Chimiak utilized oxidation of the co-amine group of amino acid derivatives with benzoyl peroxide in a new synthesis of useful derivatives of N -hydroxyornithine and N -hydroxylysine (223). The desired O-benzoyl hydroxylamine derivatives were the main products formed on oxidation. The O-benzoyl group and other protective groups may be removed easily after acetylation. It should be added that oxidation of a-amino acid esters under the same conditions leads to N-benzoylamino acid esters only (224). 

Turner s group have used Lipozyme and Novozyme as effective catalysts for the DKR of various 2-phenyl-4-substituted-5(4//)-oxazolones in the presence of an alcohol, yielding the corresponding chiral iV-benzoylamino acid esters, as shown in Scheme 3.21. 

The key step of the synthesis of new 5-(polyfluoroalkyl)-6-hydroxy-a-amino acids 81 was the hydrogenation of 2/f-pyran-2-ones 71 to the telrahydropyrones 79, which were transformed into the corresponding benzoylamino acid esters 80 by methanolysis. In all cases mixtures of diastereomeric esters 80 were formed, careful treatment of which with 15 % HCl gave a mixture of the diastereomeric benzoylamino acids 81. The latter are of interest as analogues of 2-amino-5-hydroxy valeric acid and glutamic acid [35] (Scheme 25). 

If amino acids are treated in hot acetic acid with one molecular equivalent of acetic anhydride, the corresponding acetamino acid is formed without appreciable racemization (Enoop and Blanco, 1925). However, if the proportion of acetic anhydride is increased to two equivalents, complete racemization results (Bergmann and Zervas, 1929). This loss of optical activity could also be produced by treating an active AT-acetyl- or JV-benzoylamino acid even with less than one equivalent of acetic anhydride at 100.° Amino acid esters were not racemized by this method. With peptides interesting differences were noted. Thus glycyl-L-leucine was readily racemized, but, with L-phenylalanyl-ii-tyrosine, examination of the two amino acids after hydrolysis indicated complete racemization of the tyrosyl residue and only partial loss of activity in the phenylalanine moiety. Isovaline, which does not possess a hydrogen atom in the o-position, was not affected under the conditions used. 

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