A bioactive somatostatin analog-without a type II′ β-turn:: Synthesis and conformational analysis in solution

A cyclic somatostatin analog [GRAPHICS] (1) has been synthesized. Biological assays show that this compound has strong binding affinities to somatostatin hsst2 and hsst5 receptor subtypes (5.2 and 1.2 nM, respectively, and modest affinity to hsst4 (41.1 nM)). Our conformational analysis carried out in DMSO-d(6) indicates that this compound exists as two structures arising from the trans and cis configurations of the peptide bond between Phe(7) and N-alkylated Gly(8). However, neither conformer exhibits a type II' beta -turn. This is the first report of a potent bioactive somatostatin analog that does riot exhibit a type II' beta -turn in solution. Molecular dynamics simulations (500 ps) carried out at 300 K indicate that the backbone of compound 1 is more flexible than other cyclic somatostatin analogs formed by disulfide bonds. Copyright (C) 2001 European Peptide Society and John Wiley & Sons, Ltd.