Enhancing catalytic efficiency in asymmetric Henry reaction

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Chirotechnology is a key technique in modern chemical engineering, focusing on the efficient production of chiral chemicals, a market that has grown since the 1970s. The catalytic asymmetric Henry reaction holds promise for chirotechnology, offering an economically attractive method to produce valuable chiral compounds (ß-nitroalcohols) from inexpensive achiral bulk chemicals (carbonyls and nitroalkanes). Despite its potential, this reaction has not yet been industrially adopted due to a lack of suitable catalysts that are active, enantioselective, stable, and cost-effective. While many highly enantioselective catalysts exist, they often exhibit low activity, necessitating high catalyst loadings (up to 20 mol %) to achieve acceptable product yields and enantiopurity. Two strategies to address this issue include discovering new active catalysts or enhancing existing ones through reaction and catalyst engineering. This work explores the latter approach with two catalysts: the natural enzyme hydroxynitrile lyase from Hevea brasiliensis and the artificial chiral ligand bisoxazoline. The enzyme was found to be more active in the retro-Henry reaction, leading to a racemic resolution of (rac)-2-nitro-1-phenylethanol that increased productivity tenfold. The bisoxazoline was engineered for recyclability by immobilizing it on hyperbranched polyglycerol, resulting in a “chemzyme” with high enantioselectivity (up to 86 % ee) and easy reco