Conformations of peptidomimetics formed by SNAr macrocyclizations: 13-to 16-membered ring systems

The SNAr macrocyclization products 1a-d were designed to present two amino acids residues in beta-turn conformations. Compound 1b in the series should give the most ideal fit because it could adopt a "turn - extended-pseudotu rn" orientation. To test this hypothesis, compounds 1a-d were examined by a combination of CD and NMR spectroscopic techniques, and simulated by a com putational approach that did not use constraints from spectroscopic data. G ood correspondence between the spectroscopic data and the calculated confor mations was obtained. All the compounds appear to be capable of adopting ty pe I beta-turns (or closely related states) but the bias towards this struc ture was most prevalent for the 14-membered macrocycle 1b, as predicted for the desired turn-extended-pseudo-turn conformation.