Enzymatic oxidative esterification with an unconventional regioselective control

Esters have widespread applications in nature and industry, making the strategic installation of ester bonds critical for the synthesis of pharmaceuticals, agrochemicals, polymers and other functional materials. However, achieving regioselective esterification of sterically demanding secondary alcohols in the presence of more reactive primary sites remains a formidable challenge. Here we report the engineering of aldehyde dehydrogenases into oxidative ester synthases (OxiEs) with divergent selectivities. Structure-guided protein engineering yielded two complementary catalyst classes: imidazole-dependent OxiEs1 favours primary alcohols and imidazole-independent OxiEs2 exhibits exclusive selectivity for secondary alcohols. Mechanistic studies revealed that imidazole acts as a molecular switch, allosterically tuning the active-site geometry to control regioselectivity. This system demonstrates a broad substrate scope, enabling direct, highly selective acylation of various secondary alcohols. Furthermore, we showcase its utility in controlling enantioselectivity, enabling redox-neutral synthesis and preparing valuable esters on gram-scale. This work establishes a strategy for regioselective control in esterification, transforming a classical hydride-transfer enzyme into a tunable platform for ester bond formation under mild, sustainable conditions.