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Int J Med Sci 2010; 7(1):19-28. doi:10.7150/ijms.7.19 This issue Cite

Research Paper

The Diels-Alder-Reaction with inverse-Electron-Demand, a very efficient versatile Click-Reaction Concept for proper Ligation of variable molecular Partners

Manfred Wiessler¹, Waldemar Waldeck², Christian Kliem¹, Ruediger Pipkorn³, Klaus Braun^{1 ✉}

1. German Cancer Research Center, Dept. of Imaging and Radiooncology, INF 280, D-69120 Heidelberg, Germany
2. German Cancer Research Center, Division of Biophysics of Macromolecules, INF 580, D-69120 Heidelberg, Germany
3. German Cancer Research Center, Central Peptide Synthesis Unit, INF 580, D-69120 Heidelberg, Germany

✉ Correspondence to: Dr. Klaus Braun, German Cancer Research Center (DKFZ), Dept. of Imaging and Radiooncology, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany. Tel: +49 6221 42 2495; Fax: +49 6221 42 3326. k.braunde

Abstract

The ligation of active pharmaceutical ingredients (API) for working with image processing systems in diagnostics (MRT) attracts increasing notice and scientific interest. The Diels-Alder ligation Reaction with inverse electron demand (DAR_inv) turns out to be an appropriate candidate. The DAR_inv is characterized by a specific distribution of electrons of the diene and the corresponding dienophile counterpart. Whereas the reactants in the classical Diels-Alder Reaction feature electron-rich diene and electron-poor dienophile compounds, the DAR_inv exhibits exactly the opposite distribution of electrons. Substituents with pushing electrones increase and, with pulling electrons reduce the electron density of the dienes as used in the DAR_inv.

We report here that the DAR_inv is an efficient route for coupling of multifunctional molecules like active peptides, re-formulated drugs or small molecules like the alkyalting agent temozolomide (TMZ). This is an example of our contribution to the "Click chemistry" technology. In this case TMZ is ligated by DAR_inv as a cargo to transporter molecules facilitating the passage across the cell membranes into cells and subsequently into subcellular components like the cell nucleus by using address molecules. With such constructs we achieved high local concentrations at the desired target site of pharmacological action. The DAR_inv ligation was carried out using the combination of several technologies, namely: the organic chemistry and the solid phase peptide synthesis which can produce 'tailored' solutions for questions not solely restricted to the medical diagnostics or therapy, but also result in functionalizations of various surfaces qualified amongst others also for array development.

We like to acquaint you with the DAR_inv and we like to exemplify that all ligation products were generated after a rapid and complete reaction in organic solutions at room temperature, in high purity, but also, hurdles and difficulties on the way to the TMZ-BioShuttle conjugate should be mentioned.

With this report we would like to stimulate scientists working with the focus on "Click chemistry" to intensify research with this expanding DAR_inv able to open the door for new solutions inconceivable so far.

Keywords: Click-Chemistry, Cycloaddition, Ligation chemistry, Linker Systems, Adaptor Systems, inverse Diels Alder Reaction, Tetrazines, Therapy, Triazines, Diagnostics

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