Figure 2.

The NMR structures of the five analogues studied by NMR (i.e., analogues 1, 3, 18, 19 and 21 as indicated). For each analogue, twenty energy-minimized conformers with the lowest target function are used to represent the 3D NMR structure. The bundle is obtained by overlapping the C^α atoms of all the residues. The backbone and the side chains are displayed including the disulfide bridge. The following color code is used: grey (1) H-c[Cys-Phe-Phe-dTrp-Lys-Thr-Phe-Cys]-OH, ODT-8 taken from Grace et al.;³⁴ navy-blue (3)H-c[Cys-Phe-Phe-dTrp-Lys-Thr-Phe-dCys]-OH; violet (18) Ac-c[dNcy-Phe-Phe-dTrp-Lys-Thr-Phe-Ncy]-OH; royal blue (19) Ac-c[Ncy-Phe-Phe-dTrp-Lys-Thr-Phe-Ncy]-OH; dark green (21) Ac-c[Hcy-Phe-Phe-dTrp-Lys-Thr-Phe-Cys]-OH. The amino acid side chains which are proposed to be involved in binding to the various SRIF receptors are highlighted: dTrp at position 8 in light green, Lys at position 9 in blue, and Phe at positions 6, 7 and 11 yellow. The disulphide bridges are shown in orange for clarity.