AZAPROLINE AS A BETA-TURN-INDUCER RESIDUE OPPOSED TO PROLINE

Azaproline (AzPro) is an analogue of proline containing a nitrogen ato m in place of the (CH)-H-alpha group. AzPro has been introduced in var ious model peptides, and especially in the BocAla-AzPro-Ala-NHiPr trip eptide. The structural consequence of that modification has been inves tigated in solution by using IR and H-1 NMR, with reference to the cog nate proline-containing peptide. Contrary to proline, which induces be ta-folding of the Pro-Ala sequence, azaproline apparently favors beta VI-folding of the Ala-AzPro one with high occurrence. Opening of the A zPro pyrazolidine ring to get N-methylazaalanine fundamentally does no t change the structural properties of the azatripeptide, but allows th e existence of open conformers to an extent depending on the solvent.