Asymmetric Aldol Addition by Oligopeptide Immobilized on Magnetic Particles through an Ionic Liquids Spacer

Abstract

In this work, oligopeptide was covalently bonded on the surface of magnetic particles through an ionic liquids spacer. When ionic liquids containing bulky cations with strong H-bonding ability or having hydrophobic anions were used, the yield and enantioselectivity of aldol reaction were enhanced greatly. Introducing an ionic liquids spacer between the oligopeptide and magnetic resin decreased the minimum number of amino acids for optimizing the efficiency of aldol addition. Varying the amino acid sequence of the oligopeptide showed limited effect on the yield and enantioselectivity; however, introducing a series of lysine groups on the terminal of the oligopeptide, close to the imidazolium ring, would significantly increase the output. The magnetite-loaded oligopeptide had a broader substrate range for ketone donor but restricted the enantioselectivity of aldehyde acceptor than the free oligopeptide. The combinative unit served as a recyclable catalyst for aldol addition of ketone and aldehyde, and its catalytic efficiency and selectivity can be finely designed by the characteristics of each part of the catalyst.