Development of a Phosphatase-Stable Phosphotyrosyl Mimetic Suitably Protected for the Synthesis of High-Affinity Grb2 SH2 Domain-Binding Ligands

Synthesis of (2R)-2-carboxymethyl-3-(4-(phosphonomethyl)phenyl) proprionic acid (5) in tert-butyl-protected form (6) and its use for the preparation of a Grb2 SH2 domain-directed tripeptide (8a) is reported. In extracellular ELISA-based assays, 8a exhibits potent Grb2 SH2 domain binding affinity (IC50=8 nM). Against cultures of MDA-MB-453 breast cancer cells, which over-express erbB-2 tyrosine kinase, 8a is also antimitogenic at concentrations equivalent to those required to inhibit intracellular association of Grb2 protein with phosphorylated p185erbB-2 protein (IC50=8 μM). Analogue 6 may be useful for the preparation of a variety of phosphatase-stable SH2 domain-directed ligands.