Biaryl atropisomers are common structural motifs in natural products but most importantly they are used as chiral ligands in asymmetric catalysis. Despite their utility, current methods to synthesise them are limited and lack generality. Often ligands such as QUINAP have to be synthesised as the racemate and are resolved using stoichiometric palladium which is expensive and time consuming. Biocatalytic synthesis of biaryl atropisomers offers a new alternative greener route to their production. A biocatalytic redox desymmetrisation of symmetrical biaryl diols using a mutant of galactose oxidase (M3-5) is reported. Desymmetrised biaryl atropisomers were produced in good to excellent ee and yield for a range of substrates. After the desymmetrisation a partial kinetic resolution increased the ee further as the minor enantiomer was converted to the dialdehyde. The first example of biocatalytic dynamic kinetic resolution to synthesise atropisomers asymmetrically has been developed. Freely rotating biaryl N-oxide aldehydes underwent reduction using a ketoreductase enzyme to give biaryl N-oxide products in excellent ee (96-99%). These products were found to be novel Lewis base organocatalysts for the asymmetric allylation of benzaldehyde derivatives.
|Date of Award
|1 Aug 2016
- The University of Manchester
|Jonathan Clayden (Supervisor) & Nicholas Turner (Supervisor)