Diels-Alder Reaction

Diels-Alder cycloaddition is one of the central reactions in organic synthesis and, despite its minor biological significance, has often been used in innovative approaches in catalysis research. In the context of the ''RNA world'' hypothesis, the formation of carbon-carbon bonds would be essential in anabolic pathways.

We specifically chose the reaction between anthracene and maleimide (Figure 5.3.1) for a number of reasons. Most importantly, we assumed that the completely different overall geometry of reactants and products would facilitate enrichment of catalysts that are capable of multiple turnovers. Anthracene is planar, in contrast with the @120° angles between the different rings in the Diels-Alder product. A ligand that can bind to anthracene should, therefore, not be able to bind to the product except after extensive refolding. The availability of sensitive UV absorbance and fluorescence assays for anthracene was another practical reason to choose this reaction.

Fig. 5.3.1. Diels-Alder reaction of anthracene (diene) and maleimide (dienophile).

Fig. 5.3.2. Direct selection of catalytic RNA for a Diels-Alder reaction with tether-coupled anthracene.

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