Monocarboxylic-based phosphotyrosyl mimetics in the design of GRB2 SH2 domain inhibitors

Abstract

Three monocarboxylic-containing analogues, O-carboxymethyltyrosine (cmT, 5), 4-(carboxymethyl)phenylalanine (cmF, 6), and 4-(carboxydifluoromethyl)phenylalanine (F 2cmF, 7) were utilized as phosphotyrosyl (pTyr) replacements in a high affinity β-bend mimicking platform, where they exhibited IC 50 values of 2.5 μM, 65 μM and 28 μM, respectively, in a Grb2 SH2 domain Biacore binding assay. When a terminal N α-oxalyl axillary was utilized to enhance ligand interactions with a critical SH2 domain Arg67 residue (αA-helix), binding potencies increased from 4- to 10-fold, resulting in submicromolar affinity for cmF (IC 50 = 0.6 μM) and low micromolar affinity for F 2cmF (IC 50 = 2 μM). Cell lysate binding studies also showed inhibition of cognate Grb2 binding to the p185 erbB-2 phosphoprotein in the same rank order of potency as observed in the Biacore assay. These results indicate the potential value of cmF and F 2cmF residues as pTyr mimetics for the study of Grb2 SH2 domains and suggest new strategies for improvements in inhibitor design.