Conformational analysis of cyclized dipeptide models for specific types of β-bends by two-dimensional nuclear Overhauser spectroscopy*

Abstract

The solution conformations in DMSO [dimethylsulfoxide]-d6 of the 2 cyclized dipeptides, cyclo (L-alanyl-L-alanyl-.EPSILON.-aminocaproyl) and cyclo(L-alanyl-D-alanyl-.EPSILON.-aminocaproyl), were analyzed by means of the 2-dimensional nuclear Overhauser effect (2D-NOE). The preferred conformations for the 2 compounds were deduced by comparing proton-proton distances, derived from the 2D-NOE data and relaxation-time measurements, with the corresponding distances in several possible computed low-energy conformations. The predominant conformations are a type III bend and a type II bend, respectively, for the 2 compounds. These conclusions agree with those deduced earlier on the basis of Ir and Raman spectra and circular dichroism measurements.