Selective inhibition of Src SH2 by a novel thiol-targeting tricarbonyl-modified inhibitor and mechanistic analysis by H-1/C-13 NMR spectroscopy

Detailed analysis of Sre SH2 binding by peptides containing a novel tricarb onyl-modified pTyr moiety is described. We envisaged that Src SH2 selectivi ty might be obtained by exploiting the thiol group of Cys 188 present in th e pTyr binding pocket of the protein at the beta C3 position. Peptidyl as w ell as non-peptidyl compounds 1-4 possessing a 4-alpha,beta -diketoester-mo dified pTyr mimic exhibited micromolar affinity to Src SH2. Furthermore, th ese tricarbonyl compounds were selective for Src SH2 to the extent they sho wed no significant affinity for either Cys188Ser or Cys188Ala Sre SH2 mutan ts. Upon closer examination of the binding of these tricarbonyls to Sre SH2 using NMR of C-13-labeled compounds (6a. 6b, and 6c), we found that after the initial binding event the molecule disproportionated in a 'retro-Claise n' fashion to provide benzoic acid 16 and. following hydrolysis of the meth yl ester 17, the hemiketal adduct of glyoxalic acid 18. (C) 2001 Elsevier S cience Ltd. All rights reserved.