Whole-Cell LkADH-Catalyzed Asymmetric Reduction Enables Direct Access to Cyclohexylidene Axially Chiral Alcohols.

Enantioenriched axially chiral alcohols are key building blocks for asymmetric synthesis and drug discovery, yet biocatalytic access to cyclohexylidene variants is rarely reported due to spatial separation between the hydroxyl site and chiral axis. Herein, engineered Lactobacillus kefir Alcohol Dehydrogenase (LkADH) whole-cell catalysts enable aqueous asymmetric reduction of cyclohexylidene ketones toward S-configured axially chiral alcohols. The L153K variant gave 94% conversion and 98:2 er for 2a; diverse aryl/heteroaryl substrates afforded products with high conversions and up to 99:1 er. The whole-cell strategy avoids enzyme purification and the addition of a separate purified GDH cofactor-recycling enzyme, facilitating practical synthesis verified by scale-up and downstream derivatization. This work develops a biocatalytic route and broadens the synthetic scope of LkADH reduction for uncommon axially chiral alcohols.