The protein tyrosine phosphatases (PTPs) constitute a family of closely related key regulatory enzymes that dephosphorylate phosphotyrosine residues in their protein substrates. Malfunctions in PTP activity are linked to various diseases, ranging from cancer to neurological disorders and diabetes. Consequently, PTPs have emerged as promising targets for therapeutic intervention in recent years. In this review, general aspects of PTPs and the development of small-molecule inhibitors of PTPs by both academic research groups and pharmaceutical companies are discussed. Different strategies have been successfully applied to identify potent and selective inhibitors. These studies constitute the basis for the future development of PTP inhibitors as drugs.

The total synthesis of the natural product cytostatin is described which inhibits protein phosphatase 2A. Cytostatin has anti-metastatic properties and induces apoptosis. On the basis of this synthesis the relative and absolute configuration of cytostatin could be assigned. Key structural elements of cytostatin are an alpha,beta-unsaturated lactone group and a side chain embodying a phosphate and a rather unstable (Z,Z,E)-triene subunit. In addition, the natural product carries six stereocenters. For the construction of the stereocenters reagent-controlled transformations were used in order to ensure maximum stereochemical flexibility. The Evans syn-aldol reaction was chosen to establish the stereochemistry at C-4, C-5, C-9 and C-10; C-6 was introduced by means of the Evans asymmetric alkylation. In all cases the same chiral auxiliary was employed as stereodirecting group. The stereocenter at C-11 was established by an asymmetric reduction using CBS-oxazaborolidine. Temporary protection of the phosphate group was achieved best by using the base-labile 9-fluorenylmethyl group, which could be cleanly cleaved by an excess of triethylamine; this reaction yielded analytically pure phosphates after a simple aqueous work-up. The (Z,Z,E)-triene embodied in cytostatin was synthesized by means of a Stille coupling as key transformation. The synthesis sequence established in this way readily gave access to a series of analogues with simplified structure. Initial biological testing of these analogues proved that the alpha,beta-unsaturated lactone, the C-11-hydroxy group and a fully deprotected phosphate moiety at C-9 are essential for the PP2A-inhibitory activity of cytostatin. The rather unstable triene moiety in the side chain can be replaced by other lipophilic residues with only moderate decrease of biological activity. Other phosphatases, that is, PP1, VHR, PTP1B, CD45, were not inhibited by cytostatin or any of the analogues, demonstrating the high selectivity of this compound. These findings will be useful for the design and synthesis of cytostatin-derived chemical tools for the study of biological processes influenced by PP2A.

A 10,000 member PNA-encoded library of FRET based peptides was synthesised for global analysis of protease cleavage specificity; analysis was achieved using a DNA microarray and consumed minimal quantities of enzyme (60 pmole) and library (3.5 nmole).

No abstract

Proteintyrosinphosphatasen (PTPs) bilden eine Familie eng verwandter regulatorischer Schlüsselenzyme, die Phosphotyrosinreste in ihren Proteinsubstraten dephosphorylieren. Fehlfunktionen der PTPs wurden mit mehreren Krankheiten in Verbindung gebracht, darunter mit Krebs, neurologischen Störungen und Diabetes, weshalb PTPs seit einigen Jahren als Angriffspunkte (Targets) therapeutischer Eingriffe untersucht werden. Dieser Aufsatz diskutiert allgemeine Aspekte von PTPs sowie akademische und pharmazeutisch‐industrielle Forschungsaktivitäten zur Entwicklung niedermolekularer Inhibitoren von PTPs. Zur Identifizierung wirksamer und selektiver Inhibitoren wurden unterschiedliche Strategien erfolgreich angewendet. Diese Studien bilden die Grundlage für eine mögliche künftige Entwicklung von PTP‐Inhibitoren als Wirkstoffen.

Enzymatic modifications of split and mix libraries were followed by "pulling down" onto a 2-dimensional DNA microarray, via PNA tagging; this allowed complete library interrogation of all members of the split and mix library.

Reagent‐controlled reactions are key to the introduction of the stereocenters in the total synthesis of the cytostatin isomer 1. The stereochemical flexibility of the synthesis allows efficient and convenient access to other isomers.

A 10,000 member peptide nucleic acid (PNA) encoded peptide library was prepared, treated with the Abelson tyrosine kinase (Abl), and decoded using a DNA microarray and a fluorescently labeled secondary antiphosphotyrosine antibody. A dual-color approach ensured internal referencing for each and every member of the library and the generation of robust data sets. Analysis identified 155 peptides (out of 10,000) that were strongly phosphorylated by Abl in full agreement with known Abl specificities. BLAST analysis identified known cellular Abl substrates such as c-Jun amino-terminal kinase as well as new potential target proteins such as the G-protein coupled receptor kinase 6 and diacylglycerol kinase gamma. To illustrate the generalization of this approach, two other tyrosine kinases, human epidermal growth factor 2 (Her2) and vascular endothelial growth factor receptor 2/kinase insert domain protein receptor (VEGFR2/KDR), were profiled allowing characterization of specific peptide sequences known to interact with these kinases; under these conditions Her2 was demonstrated to have a marked preference for D-proline perhaps offering a unique means of targeting and inhibiting this kinase.