Fundamental Aspects of the Chiral Modification of Platinum with Peptides: Asymmetric Induction in Hydrogenation of Activated Ketones

Abstract

A series of peptides, all containing the natural amino acid tryptophan (Trp), have been used as chiral surface modifiers for asymmetric hydrogenation reactions on alumina supported platinum catalysts. The surface chiral sites have been investigated using density functional theory calculations in order to elucidate the structure of the asymmetric environment produced by the adsorption of the peptides on the metal surface. As a test reaction, ketopantolactone (KPL) has been asymmetrically hydrogenated using the modified catalyst. Catalytic results were tested against a computational model to shed light on the phenomenon of chiral induction. The choice of Trp as the first member of the peptidic chain is due to its structural resemblance to cinchona alkaloids, already successfully used as modifiers for asymmetric hydrogenation reactions. The amino acidic moiety of Trp was elongated by addition of other natural amino acids via a peptidic bond, and the resulting peptides were tested as chiral modifiers. The ind...