Conformationally constrained phosphotyrosyl mimetics designed as monomeric Src homology 2 domain inhibitors

Inhibitors of specific src homology 2 (SH2) domain binding interactions could potentially afford new therapeutic approaches toward a variety of diseases, including several cancers. To date SH2 domain inhibitors have been confined to small phosphotyrosyl (pTyr)-containing peptides that appear to bind along the surface of SH2 domains with specific recognition features protruding into the protein. Among these protrusions is the pTyr residue itself, which is inserted into a well-formed binding pocket. In the present study monomeric pTyr mimetics were prepared having key aspects of their structure constrained to conformations of the bound pTyr residue observed in the previously reported X-ray structure of a pTyr-peptide bound to the Lck SH2 domain. The resulting constrained pTyr mimetics were examined for inhibitory potency in six SH2 domain constructs: Lck, Src, Grb2, and the C-terminal SH2 domains of PLC gamma (PLC gamma-C) and the p85 subunit of PI-3 kinase (p85-C), as well as the N-terminal SH2 domain of SH PTP2. Although inhibition constants were in the millimolar range, it was observed that capping pTyr as its N alpha-acetyl carboxamide [(L)-1] provided a roughly 2-3-fold increase in potency relative to free pTyr. Diastereomeric indanylglycine-based analogues (+/-)-3a,b were essentially inactive. Of note was methanobenzazocine (+/-)-2. While being racemic and a partial pTyr structure, this analogue retained full binding potency of the enantiomerically pure N alpha-acetyl pTyr amide (L)-1. Modification and elaboration of 2 could potentially result in small molecule inhibitors having greater potency.