Catalytic Scope of the Thiamine-Dependent Multifunctional Enzyme Cyclohexane-1,2-dione Hydrolase

The thiamine diphosphate (ThDP)‐dependent enzyme cyclohexane‐1,2‐dione hydrolase (CDH) was expressed in Escherichia coli and purified by affinity chromatography (Ni‐NTA). Recombinant CDH showed the same CC bond‐cleavage and CC bond‐formation activities as the native enzyme. Furthermore, we have shown that CDH catalyzes the asymmetric cross‐benzoin reaction of aromatic aldehydes and (decarboxylated) pyruvate (up to quantitative conversion, 92–99 % ee). CDH accepts also hydroxybenzaldehydes and nitrobenzaldehydes; these previously have not (or only in rare cases) been known as substrates of other ThDP‐dependent enzymes. On a semipreparative scale, sterically demanding 4‐(tert‐butyl)benzaldehyde and 2‐naphthaldehyde were transformed into the corresponding 2‐hydroxy ketone products in high yields. Additionally, certain benzaldehydes with electron withdrawing substituents were identified as potential inhibitors of the ligase activity of CDH. Back together: Recombinant cyclohexane‐1,2‐dione hydrolase (CDH) catalyzes the asymmetric cross‐benzoin reaction of aromatic aldehydes and pyruvate (up to quantitative conversion and 92–99 % ee). Notably, CDH accepts several aldehydes, such as hydroxybenzaldehydes, nitrobenzaldehydes, and naphthaldehydes; previously, these have only in rare cases been known as substrates of other thiamine‐dependent enzymes.