Exploration of Structural Frameworks for Reactive and Enantioselective Peptide Catalysts by Library Screenings

By screening large-scale N-terminal l-prolyl peptide libraries, we explored efficient catalysts for asymmetric Michael addition of a malonate to an enal. The catalytically active peptides obtained by the screening could be categorized into two groups based on the similarity of amino acid sequences. One group of the peptides selectively gave an S-product, whereas the other gave an R-product, despite all of the peptides having a common N-terminal sequence, Pro-d-Pro. Further optimization by second-generation screenings afforded more reactive and enantioselective catalysts. It was found that the peptides having a histidine residue at the seventh position were good catalysts, and their reaction efficiencies were correlated with the abilities of entrapping a substrate into resin beads.