Biocatalytic Site- and Stereoselective Carbonyl Desaturation for Late-Stage Functionalization of Cyclic Ketones

Direct carbonyl desaturation to prepare a,b-unsaturated carbonyl compounds is an important area of research in organic synthesis due to the significance of these molecules in medicinal chemistry and chemical biology. Despite numerous methods developed for this transformation, approaches that enable precise control over the site-selectivity of the reaction on substrates containing multiple potential reactive sites remain extremely rare, limiting their applications in late-stage functionalization of complex molecules. We report herein the engineering of ‘ene’-reductases (EREDs) for the direct carbonyl desaturation of diverse cyclic ketones to their corresponding enones with unprecedented divergent and exquisite site-selectivity. This study leverages the distinctive ability of EREDs to differentiate the stereochemical environments of hydrogens at the carbonyl b-positions. The synthetic utility of this biocatalytic platform is further demonstrated through the successful late-stage dehydrogenation on terpenoids with complementary site- selectivity to existing methods. Additionally, the method could efficiently prepare chiral enones with a b-all carbon quaternary stereogenic center via novel biocatalytic desaturative kinetic resolution. Mechanistic studies elucidate key enzyme-substrate interactions responsible for the unrivaled enzyme-controlled site-divergence.