Mixed intramolecular h-bonds of secondary thioamides

M. Hollósi, Zs Majer, M. Zewdu, F. Ruff, M. Kajtár, K. E. Kövér

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37 Citations (Scopus)

Abstract

IR and NMR studies on thioamide models containing one or more CO acceptor groups revealed the existence of three types of -CO...H-N-CS- mixed intramolecular H-bonds (MIH's) and the formation of thioamide turn conformations in nonpolar solvents. Thioacetyl alanine methyl ester (2) was found to adopt an extended or C5t conformation fixed with a 2t → 2 MIH. The dominant conformation of the N-protected dipeptide N'-methyl thioamide models 7a and 8 is a βt -turn featuring a 1←-4t MIH. 1H NOE data suggest that its φ and φ torsion angles are close to those found in β-turns of peptides. Mixed 1←13t intramolecular H-bonded conformations (γt or C7t) seem to be less favoured as a result of the repulsion between the thiocarbonyl sulphur and the Cβ group at ψ angles required for these conformations.

Original languageEnglish
Pages (from-to)195-202
Number of pages8
JournalTetrahedron
Volume44
Issue number1
DOIs
Publication statusPublished - 1988

ASJC Scopus subject areas

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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