Synthesis and evaluation of 3-Phenylpyrazolo[3,4-d]pyrimidine-peptide conjugates as Src kinase inhibitors

3 Phenylpyrozolo[3,4-d]pyrimidine (PhPP) derivatives substituted with an alkyl or aryl carboxylic acid at the N1-endocyclic amine, such as PhPP-CH2COOH (IC50=250 mu m), and peptides Ac-CIYKYY (IC50=400 mu m) and Ac-YIYGSFK (IC50=570 mu m) were weak inhibitors of polyE(4)Y phosphorylation by active c-Src. A series of PhPP-peptide conjugates were synthesized using PhPP as an ATP mimic and CIYKYY or YIYGSFK as a peptide substrate to improve the inhibitory potency against active c-Src kinose. PhPP derivatives were attached to the N terminus or the side chain of amino acids in the peptide template. Two N-terminal substituted conjugates, PhPP-CH2CO-CIYKYY (IC50=0.38 mu m) and PhPP-CH2CO-YIYGSFK (IC50 = 2.7 mu m), inhibited the polyE(4)Y phosphorylation by active c-Src significantly higher than that of the parent compounds. The conjugation of PhPP with the peptides produced a synergistic inhibition effect possibly through creation of favorable interactions between the conjugate and the kinase domain as shown by molecular modeling studies.