Evaluation of Lactam-Bridged Neurotensin Analogues Adjusting ψ(Pro10) Close to the Experimentally Derived Bioactive Conformation of NT(8−13)

The neurotensin C-terminal hexapeptide, NT(8-13), which has been found to adopt a beta-strand-like conformation while bound to the NT1 receptor, was modified by the introduction of conformational constraints. Synthesis of the four stereoisomeric 4.4-spirolactams 1-4 and subsequent NT1 receptor binding studies showed that the restriction of psi(Pro10) to approximately 130 degrees leads to a more than 1000-fold increase of binding affinity for 1 (Ki = 12 nM) when compared to the more flexible analogue [NMeTyr11]NT(8-13).