[Stereochemistry of the reductive amination of 4-oxoproline derivatives with glycine esters].

An amination of 4-oxoproline derivatives with glycine methyl or benzyl ester and sodium cyanoborohydride led to the mixtures of corresponding diastereomeric 4-cis- and 4-trans-glycinoproline derivatives. We found that the ratio of diastereomers mainly depends on the structure of 4-oxoproline ester groups and, to a lesser extent, on the structure of N-acyl substituents. The best results were achieved with tert-butyl ester group; it ensured good yields of the amination products and the greatest prevalence of 4-cis-isomers.

[Synthesis isomeric 4-prolylamines and 4,4'-diprolylamines].

Starting from the previously described tert-butyl esters of 4-epimeric N-benzyloxycarbonyl-4-hydroxyprolines and N-benzyloxycarbonyl-4-trans- and 4-cis-trifluoroacetamidoproline tert-butyl esters, the corresponding un-protected 4-aminoprolines and a number of their partially protected derivatives were synthesized via the intermediate 4-O-mesyl and 4-azide derivatives. The reductive amination of N-benzyloxycarbonyl-4-oxoproline tert-butyl ester with ammonium acetate led to N-benzyloxycarbonyl-4-cis-4'-cis- and 4-cis-4'-trans-diprolinylamines. The 1H NMR and CD spectra of the synthesized compounds are described.

[Hydrolysis of primary amide groups in Asn/Gln-containing peptides].

Peptides Boc-Ala-Asn/Gln-OH and Boc-Asn/Gln-Ala-OH were saponified with barium hydroxide to corresponding Asp/Glu-containing peptides. Under the conditions of saponification, Boc-Asn-Ala-OH additionally afforded Boc-Asp-OH, isopeptide Boc-Asp(Ala)-OH, and Boc-NHSuc > Ala-OH, with the third being the key intermediate in these transformations. Boc-Asp(OMe)-Ala-OMe underwent similar transformations under treatment with diazomethane or triethylamine.