THE ETHYLENE GROUP AS A PEPTIDE-BOND MIMICKING UNIT - A THEORETICAL CONFORMATIONAL-ANALYSIS

One of the features of the polypeptide backbone is that it represents a flexible chain that contains almost rigid CO-NH peptide bonds. One may try to substitute one or more such bonds by another relatively rigid unit to maintain the overall conformational properties of the backbone and at the same time modify some other properties of the molecule (''pseudopeptide''), such as the ability to form hydrogen bonds. By a detailed conformational analysis, it is shown that the carbon-carbon double bond is quite isosteric with the peptide bond and for this reason suitable for such a substitution. This is accomplished by applying molecular mechanics in calculation of the phi, psi maps for pseudopeptide analogs of the N-acetyl-Ala-NHMe molecule.