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

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 Braun1 ✉

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

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Wiessler M, Waldeck W, Kliem C, Pipkorn R, Braun K. The Diels-Alder-Reaction with inverse-Electron-Demand, a very efficient versatile Click-Reaction Concept for proper Ligation of variable molecular Partners. Int J Med Sci 2010; 7(1):19-28. doi:10.7150/ijms.7.19. Available from

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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 (DARinv) turns out to be an appropriate candidate. The DARinv 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 DARinv 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 DARinv.

We report here that the DARinv 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 DARinv 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 DARinv 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 DARinv 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 DARinv 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