SOLUTION CONFORMATION OF A PENTAPEPTIDE BY NMR AND MOLECULAR MODELING STUDIES

High resolution NMR studies and molecular modeling calculations were performed on a linear pentapeptide BOC-Tyr-Gly-Gly-Pro-Leu-OMe. This molecule exhibits two conformations in the solution state. While the C-13 spectrum in nonpolar solvents such as acetonitrile shows only one form, in DMSO-d6 and MeOD there are two forms. The appearance of the major (M) and minor (m) resonances is attributed to cis-trans isomerization about the X-Pro bond. The assignments of several proton resonances for the major conformer were made through the combined analysis of two dimensional (2D) homonuclear correlated spectroscopy (COSY) and available data on similar peptides. The solution conformation of the major moiety was probed using the distance constraints obtained from 2D-NOE spectroscopy (NOESY). In addition, other information such as presence of internal hydrogen bonds and dihedral angle values from coupling constants for the amide protons were also used.