Investigations on a flexible prolyl-endopeptidase inhibitor in solution by NMR techniques

4-Phenylbutyrylprolylpyrrolidine, an inhibitor of prolyl-endopeptidase, exists in solution as an equilibrium of trans and cis prolyl rotamers. The equilibrium ratio and the exchange rate of the rotamers were measured in several solvents. The conformational preferences of the flexible molecule were studied by NMR, based on proton–proton vicinal coupling constants, NOESY cross peak intensities and aromatic ring current shifts. Copyright  1999 John Wiley & Sons, Ltd.