Enantioselective Biocascade Catalysis with a Single Multifunctional Enzyme

Abstract

Asymmetric catalytic cascade processes offer direct access to complex chiral molecules from simple substrates and in a single step. In biocatalysis, cascades are generally designed by combining multiple enzymes, each catalyzing individual steps of a sequence. Herein, we report a different strategy for biocascades based on a single multifunctional enzyme that can promote multiple stereoselective steps of a domino process by mastering distinct catalytic mechanisms of substrate activation in a sequential way. Specifically, we have used an engineered 4-oxalocrotonate tautomerase (4-OT) enzyme with the ability to form both enamines and iminium ions and combine their mechanisms of catalysis in a complex sequence. This approach allowed us to activate aldehydes and enals toward the synthesis of enantiopure cyclohexene carbaldehydes. The multifunctional 4-OT enzymes could promote both a two-component reaction and a triple cascade characterized by different mechanisms and activation sequences.

Multifunctional Biocatalysts for Organic Synthesis

“…More recently, enamine and iminium carbonyl activation by 4-OT has been further explored in the development of biocatalytic reactions that created up to 3 new C−C bonds using a single enzyme. 15 The authors designed a tandem-fused 4-OT variant from Pseudomonas putida containing an internal His-Tag, Pp-4-OT-F 3 , for remarkable two-and threecomponent reactions for the synthesis of densely functionalized cyclohexene carbaldehydes 10. In the two-component cascade system, various electron-rich and -poor cinnamaldehydes combined with nitromethane 4 could be converted by an iminium−iminium-enamine sequence to cyclohexene carbaldehydes 10.…”

“…More recently, enamine and iminium carbonyl activation by 4-OT has been further explored in the development of biocatalytic reactions that created up to 3 new C–C bonds using a single enzyme . The authors designed a tandem-fused 4-OT variant from Pseudomonas putida containing an internal His-Tag, Pp-4-OT-F 3 , for remarkable two- and three-component reactions for the synthesis of densely functionalized cyclohexene carbaldehydes 10 .…”

A New Age of Biocatalysis Enabled by Generic Activation Modes

“…A recent example combines iminium with Lewis acid activation for asymmetric Michael addition within one enzyme . In another study, a single active site proline has been utilized for both, enamine and iminium activation, to form various C–C bonds by one multifunctional enzyme . In addition, synergistic catalysis by two activation modes can also be achieved in combined chemo-biocatalytic processes, in particular through synergistic bio- and photocatalysis. − An exemplary instance involves the production of amino acids possessing several stereocenters (Figure c).…”

Acetaldehyde in the Enders triple cascade reaction via acetaldehyde dimethyl acetal

“…In this elegant cascade process, catalyst 1 promotes three consecutive carbon-carbon bond forming steps generating four stereogenic centers with high diastereoselectivity and complete enantiocontrol (Scheme 1). This elegantly designed example established a new direction in asymmetric aminocatalysis, leading to an impressive growth of methods based on organocascade processes [8,10,[13][14][15][16]. The experimental simplicity of the strategy offers the potential of rapidly increasing structural and stereochemical complexity starting from readily available substrates.…”