Conformational study of a somatostatin analogue by high-field n.m.r. spectroscopy, in aqueous solution

Abstract

The cyclic analogue of somatostatin (SRIF), D-Phe-Cys-Tyr-D-Trp-Lys-Thr-Cys-Thr-NH2 (CTC), exhibits good affinity for both opioid and SRIF receptor systems. Its conformational properties were examined in water by high-field proton n.m.r. spectroscopy and compared with results previously obtained with structurally related analogues SMS 201-995 and Sandoz 204-090 in the same solvent. The assignments were made using 2 D-n.m.r. methods, especially long-range connectivities between neighbouring alpha protons, and between beta and aromatic protons. The 3JNH-C alpha H and delta delta/delta T values are compatible with an equilibrium between two gamma turns involving residues 2, 3 and 4 and residues 3, 4, and 5, respectively.