Amphiphilic polymer supports for the asymmetric hydrogenation of amino acid precursors in water

Abstract

This paper describes the synthesis and characterization of a new class of amphiphilic, water-soluble diblock copolymers based on 2-oxazoline derivatives with pendent (2S,4S)-4-diphenylphosphino-2-(diphenylphosphinomethyl)pyrrolidine (PPM) units in the hydrophobic block. The synthetic strategy involves the preparation of a diblock copolymer precursor with ester functionalities in the side chain; which were converted into carboxylic acids in a polymer-analogous step and finally reacted with the PPM ligand. The structures of the copolymers were characterized by 1H and 31P NMR spectroscopy and GPC measurements. Subsequently, these polymers were successfully utilized as a polymeric support for the asymmetric hydrogenation of 1) (Z)-α-acetamido cinnamic acid and 2) methyl (Z)-α-acetamido cinnamate in water, showing 90% substrate conversion at 25 °C within 20 minutes at atmospheric H2 pressure (1 bar) for methyl (Z)-α-acetamido cinnamate.