AZA-PEPTIDES .3. EXPERIMENTAL STRUCTURAL-ANALYSIS OF AZA-ALANINE AND AZA-ASPARAGINE-CONTAINING PEPTIDES

To determine the structural perturbations induced by the (CH)-H-alpha- ->N-alpha exchange in aza-peptides, we have examined by H-1 NMR and IR spectroscopy various derivatives of the aza-analogues of alanine, asp artic acid and asparagine in different organic solvents with increasin g polarity. Their general formulas are: R-1-AzXaa-(NRR3)-R-2, R-1-Pro- AzXaa-(NRR3)-R-2 and R-1-AzXaa-Pro-(NRR3)-R-2 (where AzXaa denotes the aza-analogue of the amino acid residue Xaa = Ala, Asp, Asn; R-1 = Boc , Z; R-2, R-3 = H, Me, iPr). The aza-analogue of an amino acid residue appears to be a strong beta-turn-inducing motif, and the AzAsn carbox amide side-chain is capable of interacting, as a proton donor, with th e preceding peptide carbonyl group. (C) Munksgaard 1997.