Exploration of Aldol Reactions Catalyzed by Stereoselective Pyruvate Aldolases with 2‐Oxobutyric Acid as Nucleophile

Pyruvate aldolases from Pfam family PF03328, recently described to be able to use hydroxypyruvic acid as nucleophile substrate, were shown to also catalyse aldol adducts formation from 2‐oxobutyric acid. A 1H NMR‐based assay was used to screen 21 aldolases for their activity towards 2‐oxobutyric acid and to predict their stereoselectivity at position 3 of the aldol adducts. The best biocatalysts were then proved to be strictly (3S)‐selective. Contrary to known enzymes from this family that are seldom stereoselective at position 4, three aldolases were highlighted as allowing a selective access to (3S,4R) or (3S,4S) aldols. Seven 3‐deoxy‐3‐methylulosonic acids never described before were finally prepared and isolated with good yields and stereoselectivities.