Potent low molecular weight substrates for protein-tyrosine phosphatase

The ability of protein-tyrosine phosphatases (PTPases) to catalyze the hydrolysis of simple aromatic phosphates has been recognized for some time. However, these compounds are significantly poorer substrates than their peptide-based counterparts containing phosphotyrosine. Consequently, the effort to create potent PTPase substrates has predominately focused on the use of peptidic carriers to deliver the phosphotyrosine moiety to the enzyme active site. We now report the synthesis and evaluation of several low molecular weight aromatic phosphates that serve as robust substrates for the rat PTPase, PTP1. We initially surveyed the ability of PTP1 to catalyze the hydrolysis of a variety of phenyl phosphate structural variants. Sterically demanding substituents positioned ortho and (to a lesser extent) meta to the phosphate group severely compromise the ability of these species to serve as phosphatase substrates. However, both benzylic and negatively charged substituents para to the hydrolyzable phosphate dramatically promote hydrolytic efficiency, which appears to be augmented through a dramatic enhancement in the affinity of the substrate for PTP1. The best substrate examined in this study exhibits a K-m of 16 +/- 3 mu M. In addition, it serves as an inhibitor of the PTP1-catalyzed hydrolysis of p-nitrophenyl phosphate with a K-i of 4.9 +/- 0.7 mu M. The extraordinary structural simplicity of this compound, as well as those of several others described herein, provides a promising starting point for the design of potent PTPase inhibitors.