[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure.

"Catalyst -substrate coimmobilization" has been used for the discovery of highly active and selective peptidic catalysts for asymmetric aldol reactions within split-and-mix libraries. This screening method is based on the coimmobilization of one reaction partner along with each library member via a bifunctional linker on the library beads followed by mixing of this library with a labeled second reaction partner. Here we discuss the details of the combinatorial screening and demonstrate that the exchange of the bead-bound and the labeled reaction components leads to the same hits within the library.

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Enantioselective syntheses O 0031Increased Structural Complexity Leads to Higher Activity: Peptides as Efficient and Versatile Catalysts for Asymmetric Aldol Reactions. -Tripeptides (I) and (II) are significantly more active than proline as catalysts for asymmetric aldol reactions. Equally high catalytic activities are observed with a variety of aldehydes under otherwise identical conditions. Compared to proline, similar yields are obtained using 10 mol% of (I) and only 1 mol% of (II). The catalysts generate aldol products with opposite absolute configurations, thus showing the possibility for tuning the enantioselectivity by simple modifications in the secondary structure. -(KRATTIGER, P.; KOVASY, R.; REVELL, J. D.; IVAN, S.; WENNEMERS*, H.; Org. Lett. 7 (2005) 6, 1101-1103; Dep. Chem., Univ. Basel, CH-4056 Basel, Switz.; Eng.) -R. Steudel 33-030