Reaction mechanisms in peptide synthesis. Part 2. Tautomerism of the peptide bond |
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Authors: | Jerzy Ciarkowski Francis M F Chen N Leo Benoiton |
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Institution: | (1) Department of Biochemistry, Faculty of Medicine, University of Ottawa, K1H 8M5 Ottawa, Ont., Canada;(2) Present address: University of Gdansk, Poland |
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Abstract: | Summary We had concluded in previous work that ring opening of a 2-alkyl-5(4H)-oxazolone by water or ammonia leads to transient high-energy imidol intermediates which instantly tautomerize to the native amides. Using the MOPAC molecular orbital program, detailed geometric and energetic characteristics of the tautomerism of a peptide bond have been determined on the AM1 level. The results demonstrate that tautomerism of a peptide bond comprises a three-stage process involving three successive transition states and a bimolecular mechanism: (i) E Z peptide bond isomerization followed by dimerization, (ii) concerted double-hydrogen exchange leading to an -hydroxyimine (imidic acid) followed by splitting of the dimer, and (iii) Z E N-methylimine inversion. While pathway (iii ii i) is predicted as a feasible route terminating in the formation of a peptide bond, the inverse route (iii ii i) is excluded as a possible initial step in the generation of a 5(4H)-oxazolone intermediate. |
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Keywords: | AM1 MOPAC N-Acetyglycine amide -Hydroxyimine" target="_blank">gif" alt="agr" align="BASELINE" BORDER="0">-Hydroxyimine Dimerization Hydrogen exchange |
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