Nucleophile Promiscuity of Engineered Class II Pyruvate Aldolase YfaU from E. Coli

Pyruvate‐dependent aldolases exhibit a stringent selectivity for pyruvate, limiting application of their synthetic potential, which is a drawback shared with other existing aldolases. Structure‐guided rational protein engineering rendered a 2‐keto‐3‐deoxy‐ l ‐rhamnonate aldolase variant, fused with a maltose‐binding protein (MBP‐YfaU W23V/L216A), capable of efficiently converting larger pyruvate analogues, for example, those with linear and branched aliphatic chains, in aldol addition reactions. Combination of these nucleophiles with N ‐Cbz‐alaninal (Cbz=benzyloxycarbonyl) and N ‐Cbz‐prolinal electrophiles gave access to chiral building blocks, for example, derivatives of (2 S ,3 S ,4 R )‐4‐amino‐3‐hydroxy‐2‐methylpentanoic acid (68 %, d.r. 90:10) and the enantiomer of dolaproine (33 %, d.r. 94:6) as well as a collection of unprecedented α‐amino acid derivatives of the proline and pyrrolizidine type. Conversions varied between 6–93 % and diastereomeric ratios from 50:50 to 95:5 depending on the nucleophilic and electrophilic components.