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Jian Xie is from Hunan province, People’s Republic of China. After graduated from the group of Prof. Zhitang Huang in Institute of Chemistry, Chinese Academy of Sciences in 2000, he joined Prof. Christopher T. Seto’s group in Department of Chemistry, Brown University, working on the synthesis and properties study of Protein Tyrosine Phosphatase inhibitors. It’s well known that protein tyrosine phosphatases (PTPase) play very important roles in the cell activities. Opposing actions of PTPase and PTKase (protein tyrosine kinase) regulate the reversible tyrosine phosphorylation and dephosphorylation of proteins, which subsequently control the cell growth, mitogenesis, motility, cell-cell interaction, metabolism, gene transcription and the immune response, etc. Defective or inappropriate PTPase operation can result in wide spread diseases such as diabetes, cancers and immune dysfunctions. It has been found out that overexpressed PTPases such as PTP1B might induce Type II diabetes. Yersinia PTPase was found to be the important virulent determinant in the Black Death, or the Bubonic plague. Another interesting example is PTP1B-deficient mice showed increased insulin sensitivity and obesity resistance. All these studies suggest that inhibition against PTPases is an interesting drug target. Our previous research found that -ketoacid can work as the mimic of the phosphate. Recently it has been reported that there are two binding sites in the PTPase for substrate. This instantly suggests a method of improving the inhibitor binding affinity by incorporating two aryl -ketoacid moieties into one single inhibitor structure. Jian Xie is working on library synthesis based on diamine backbone. Assay on crude inhibitors affords a relatively quick screening method. Latest results show that squaric acid is a new mimic of phosphate group.