Enantioselective Biocatalytic Mannich Reaction for the Synthesis of Cyclic Sulfonamides by an Artificial Enzyme

The sulfonamide motif is a privileged pharmacophore found in numerous therapeutics, and seven-membered cyclic sulfonamides in particular are valued for their structural and biological properties. However, study on the synthesis of chiral sulfonamides via enzymatic catalysis remains rare. Herein, we report the directed evolution and mechanistic characterization of an artificial Mannichase that promotes an asymmetric biocatalytic Mannich reaction between cyclic ketones and cyclic sulfonyl-imines through an enamine activation pathway. Iterative rounds of engineering delivered variants that furnish seven-membered cyclic sulfonamide products with high stereoselectivity (up to 95.5:4.5 e.r., >20:1 d.r.) and reactivity (up to >99% yield). Complementary molecular dynamics and QM/MM calculations reveal key active-site interactions and transition-state features that underlie the observed stereoselectivity. This work expands the toolkit of biocatalytic Mannichases, establishes a practical route to enantioenriched cyclic sulfonamides, and highlights the power of combining the covalent anchoring strategy with directed evolution to access new-to-nature asymmetric transformations with potential applications in medicinal chemistry.