Syntheses and activities of backbone-side chain cyclic octapeptide ligands with N-functionalized phosphotyrosine for the N-terminal SH2-domain of the protein tyrosine phosphatase SHP-1.

The protein tyrosine phosphatase SHP-1 plays an important role in many physiological and pathophysiological processes. This phosphatase is activated through binding of ligands to its SH2-domains, mainly to the N-terminal one. Based on a theoretical docking model, backbone-to-side chain cyclized octapeptides were designed as ligands. Assembly of such modelled structures required the synthesis of N-functionalized tyrosine derivatives and their incorporation into the sequence. Because of difficulties encountered in the condensation of N-protected amino acids to the N-alkylated tyrosine-peptide we synthesized and used preformed dipeptide building units. As all attempts to obtain phosphorylated dipeptide units failed, the syntheses had to be performed with a free phenolic function. Use of different N-alkyl or cycloalkyl residues in the N-functionalized side chains allowed to investigate the effect of ring size, flexibility and hydrophobicity of formed lactam bridges on stimulatory activity. All tested linear and cyclic octapeptides stimulate the phosphatase activity of SHP-1. Stimulatory activities of cyclic ligands increase with the chain length of the lactam bridges resulting in increased flexibility and better entropic preformation of the binding conformation. The strong activity of some cyclic octapeptides supports the modelled structure.