Rhenium-labeled somatostatin analog RC-160: ¹H NMR and computer modeling conformational analysis

The solution conformations of RC-160, cyclic n-Phe¹-Cys²-Tyr³-D-Trp⁴-Lys ⁵-Val⁶-Cys⁷-Trp⁸-NH₂, an analog of the tumor antiproliferatory neuropeptide somatostatin, and RC-160 labeled with rhenium (Re-RC-160), have been determined by using two-dimensional ¹H NMR spectroscopy (600 MHz) and restrained molecular dynamics simulations. Re-RC-160 yields the same average solution conformation as does the apo form with an antiparallel β-sheet fold and a type II′ β-turn centered at D-Trp⁴-Lys⁵. These results indicate that the spatial topography of the side chains essential for somatostatin receptor binding is maintained in Re-RC-160.