Aldolase and N-heterocyclic carbene gold(i) catalysts: compartmentalization and immobilization on anionic clays for concurrent hybrid catalysis at acidic pH

Abstract

One of the last limitation to concurrent reactions involving hybrid catalysis is pH. This has been solved by mixing a catalyst, operating at acidic pH, and an aldolase, through enzyme...

Hybrid Catalysis in Concurrent Mode: How to Make Catalysts and Biocatalysts Compatible?

“…More precisely, a N-heterocyclic (NHC) gold complex (Scheme 8A), in charge of the hydration of an alkyne into a ketone, was mixed with fructose-6-phosphate aldolase (FSA), tasked with the subsequent conversion of the ketone into a chiral aldol. [27] To shield FSA from this low pH, it was kept encapsulated in E. coli cells, since it is known that several microorganisms can survive in harsh conditions while maintaining their internal pH close to neutrality. [28] Unfortunately, despite the aldolization can occur at pH 3 thanks to the cells protection, two problems arose that needed to be solved i) the NHC gold complex was inactivated upon contact with the cell membrane (probably due to the presence of thiols), and ii) the high temperature (60 °C) required to achieve the catalystassisted hydration reaction compromised FSA protection.…”

“…It involved a chemical catalyst that required a pH below 3 to function properly due to the protodeauration step in the catalytic cycle, being combined with an enzyme having an optimum pH of 8. More precisely, a N ‐heterocyclic (NHC) gold complex (Scheme 8A), in charge of the hydration of an alkyne into a ketone, was mixed with fructose‐6‐phosphate aldolase (FSA), tasked with the subsequent conversion of the ketone into a chiral aldol [27] . To shield FSA from this low pH, it was kept encapsulated in E. coli cells, since it is known that several microorganisms can survive in harsh conditions while maintaining their internal pH close to neutrality [28] .…”

Enantioselective merged gold/organocatalysis

“…Herein, we report an overview focusing on the state of the art in the field of enantioselective merged gold/organocatalysis. It should be noted that the reports regarding the combination of gold catalysis with enzyme catalysis 17 remains out of the scope of our discussion. For a better understanding of the operating catalytic modes, the transformations are discussed based on our previous proposition on sequential, relay and cooperative catalysis (Scheme 1c).…”

Identification of key active residues and solution conditions that affect peptide-catalyzed ester hydrolysis

“…Enzymes provide incredible opportunities for highly precise catalytic reactivity. 1–10 They drive a vast swath of different catalytic reactions, ranging from the synthesis of chiral alcohols to interfacial hydrolysis of ester bonds. 11,12 In general, the specificity of the reaction is precisely tuned to substrate structure, which is critically important for biological processes.…”