Y--X--C(R').dbd.C(R")COOR'" (A1) The present invention relates to novel protein tyrosine phosphatase modulating compounds having the general structure shown in Formula (A1), to methods for their preparation, to compositions comprising the compounds, to their use for treatment of human and animal disorders, to their use for purification of proteins or glycoproteins, and to their use in diagnosis. The invention relates to modulation of the activity of molecules with phosphotyrosine recognition units, including protein tyrosine phosphatases (PTPases) and proteins with Src-homology-2 domains, in in vitro systems, microorganisms, eukaryoic cells, whole animals and human beings. R' and R" are independently selected from the group consisting of hydrogen, halo, cyano, nitro, trihalomethyl, alkyl, arylalkyl. R'" is selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, arylalkyl. X is aryl. Y is selected from hydrogen or ##STR1## wherein (*) indicates a potential point of attachment to X.