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Substrate-Catalyst Co-immobilization

Our group has developed a method based on the immobilization of one reaction partner and each library member, the potential catalyst, on the same bead [20]. This can easily be accomplished by means of a bifunctional linker that carries on one end the reactant A and on the other end the library member (Figure 5.4.7). If the reaction partner B is labeled with, e.g., a dye, a fluorophore, or radioactivity a reaction between A and B leads to the covalent attachment of the marker to those beads that carry catalytically active library members. These beads are then readily detected with a low-power microscope.

The feasibility of the method was demonstrated by testing the members of a tri-peptide library for their ability to catalyze the acylation of an alcohol (reactant A) by a dye-marked pentafluorophenyl (Pfp) ester (reactant B).

Fig. 5.4.7. Co-immobilization of potential catalyst and reactant (A) on the same bead. In the example only compound 2 is an active catalyst.

The library was designed not to contain amino acids that could be self-acylated, thus Ser, Thr, Lys, and Cys were not part of the library. His was incorporated as a known weak acylation catalyst and was expected to be selected. After reacting the library with the dye-marked Pfp ester, and thorough washing, several beads remained red, indicating covalent attachment of the dye to the resin beads. Analysis of the peptides on these red beads showed that each active bead carried at least one His. There is, therefore, no cross catalysis between different beads. The method can be used to search for catalysts of any bimolecular reaction in which one reaction partner can be attached to a solid support and the other labeled with a dye, a fluorophore, or radioactivity.

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