Production of ( S )‐β‐Nitro Alcohols by Enantioselective C−C Bond Cleavage with an R ‐Selective Hydroxynitrile Lyase

Hydroxynitrile lyase (HNL)‐catalysed stereoselective synthesis of β‐nitro alcohols from aldehydes and nitroalkanes is considered an efficient biocatalytic approach. However, only one S ‐selective HNL— Hevea brasiliensis ( Hb HNL)—exists that is appropriate for the synthesis of ( S )‐β‐nitro alcohols from the corresponding aldehydes. Further, synthesis catalysed by Hb HNL is limited by low specific activity and moderate yields. We have prepared a number of ( S )‐β‐nitro alcohols, by kinetic resolution with the aid of an R ‐selective HNL from Arabidopsis thaliana ( At HNL). Optimization of the reaction conditions for At HNL‐catalysed stereoselective C−C bond cleavage of racemic 2‐nitro‐1‐phenylethanol (NPE) produced ( S )‐NPE (together with benzaldehyde and nitromethane, largely from the R enantiomer) in up to 99 % ee and with 47 % conversion. This is the fastest HNL‐catalysed route known so far for the synthesis of a series of ( S )‐β‐nitro alcohols. This approach widens the application of At HNL for the synthesis not only of ( R )‐ but also of ( S )‐β‐nitro alcohols from the appropriate substrates. Without the need for the discovery of a new enzyme, but rather by use of a retro‐Henry approach, it was used to generate a number of ( S )‐β‐nitro alcohols by taking advantage of the substrate selectivity of At HNL.