STRUCTURES, DYNAMICS, AND BIOLOGICAL-ACTIVITIES OF 15 CYCLIC HEXAPEPTIDE ANALOGS OF THE ALPHA-AMYLASE INHIBITOR TENDAMISTAT (HOE-467) IN SOLUTION

The design, synthesis, and conformational analysis of a series of 15 c yclic hexapeptides as analogs of the active sequence of the alpha-amyl ase inhibitor protein Tendamistat (HOE 467) Ser(17)-Trp(18)-Arg(19)-Ty r(20) are described. A template-oriented peptide design strategy was u sed to expose this tetrapeptide motif to different conformational envi ronments. Conformational analysis was carried out for each peptide in DMSO-d(6) solution by means of MMR spectroscopy. For structure determi nation, restrained molecular dynamics (MD) simulations in vacuo and in DMSO based on experimentally derived distance and torsion constraints were performed. For eight peptides, experimental data were found to b e inconsistent unless multiple fast interconverting backbone conformer s were taken into account. For these peptides the NMR observables can only be described by averaging over conformational ensembles containin g at least two major backbone conformations. All other compounds can b e described by a single backbone conformation. Some general rules for rigidification of peptide backbone conformations can be verified by an alyzing different peptide structures. It could further be shown that t he use of backbone templates forces the tetrapeptide sequence to adopt its native conformation, as found in solution and crystal structures of Tendamistat. Significant biological activity as a-amylase inhibitor s could be measured for these peptides. However, the suggested active tetrapeptide sequence alone is not responsible for the strong binding between Tendamistat and cl-amylase, which is supported by the inspecti on of the preliminary solid-state structure of the Tendamistat/alpha-a mylase complex.