The hydrolysis of primary amide groups in Asn/Gln-containing peptides
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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. Saponification with barium hydroxide was accompanied by a high epimerization ofN-terminal amino acid residues, whereas the products of the diazomethane treatment of Boc-Asp(OMe)-Ala-OMe had a low degree of epimerization.
Key wordsasparagine aspartic acid glutamine glutamic acid peptides epimerization rearrangement primary amides selective saponification
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