Four Atom Efficient Enzyme Cascades for All 4-Methoxyphenyl-1,2-propanediol Isomers Including Product Crystallization Targeting High Product Concentrations and Excellent E-Factors

Atom economy and E-factor calculations are valuable tools in the sustainable process design of fine and pharmaceutical chemicals. Adjoined with the smart assembly of biocatalysts in artificial cascades, fine and pharmaceutical chemicals can be produced with high efficiency and selectivity, while also reducing the ecological footprint. In this study, all four isomers of 4-methoxyphenyl-1,2-propanediol, a potential anti-inflammatory drug, are synthesized by stereocomplementary carboligases and NADPH-dependent alcohol dehydrogenases in a one-pot, two-step cascade with isomeric purities of >99%. The consumed NADPH in the second step is regenerated by the same alcohol dehydrogenase (ADH) with an auxiliary substrate, which allows coproduct recycling into the first step to form a self-sufficient cascade and increase atom economy to 99.9%. In addition, a hydrophobic microaqueous reaction system (MARS) enabled space-time yields (STYs) of up to 165 g L-1 day(-1) for the respective product isomers. The employment of this organic reaction environment facilitates product crystallization with an isolated yield of 38% and crystal purities of 99.9%. Crystal separation by filtration allows any required substrate surplus to be reapplied in a next batch, thus reducing the E-factor potentially close to 1.