Synthesis of enantioenriched atropisomers by biocatalytic deracemization.

The synthesis of enantiopure materials is vital for pharmaceutical and agrochemical industries owing to the inherently chiral nature of biological systems and the fact that two enantiomers can have markedly different biochemical properties1. In particular, enantioselective preparation of atropisomers is of great interest owing to their privileged status as chiral ligands and pharmacophores2-4. Although chromatographic- or crystallization-based methods are commonly used to separate atropisomers, we urgently need more efficient and economical approaches to access enantioenriched atropisomers5,6. The use of stereoconvergent methods to access molecules with point chirality is well established but we have not tapped the potential of stereoconvergent catalytic methods to arrive at enantioenriched atropisomers. Here we report deracemization activity of a P450 enzyme and explore its ability to deliver a stereoconvergent route towards enantioenriched atropisomers. Using a curated set of P450 variants, we found that a wide variety of symmetric and non-symmetrically substituted 2,2'-binaphthol (BINOL) building blocks can be deracemized to high enantiomeric purity. This deracemization activity is mechanistically distinct from the activity of previously reported P450 enzymes, which operate through enantioselective bond formation to afford enantioenriched atropisomers. By contrast, the deracemization process reported here is proposed to proceed through bond rotation. As engineered variants have complementary selectivity profiles and substrate scope, this biocatalytic platform should be readily tunable for any desired substitution pattern. We anticipate that these results will inspire new stereoconvergent approaches to synthesizing conformationally stable atropisomers.