Enantioselective Reductive Oligomerization of Carbon Dioxide into l-Erythrulose via a Chemoenzymatic Catalysis.

A cell-free enantioselective transformation of the carbon atom of CO has never been reported. In the urgent context of transforming CO into products of high value, the enantiocontrolled synthesis of chiral compounds from CO would be highly desirable. Using an original hybrid chemoenzymatic catalytic process, we report herein the reductive oligomerization of CO into C (dihydroxyacetone, DHA) and C (l-erythrulose) carbohydrates, with perfect enantioselectivity of the latter chiral product. This was achieved with the key intermediacy of formaldehyde. CO is first reduced selectively by 4e by an iron-catalyzed hydroboration reaction, leading to the isolation and complete characterization of a new bis(boryl)acetal compound derived from dimesitylborane. In an aqueous buffer solution at 30 °C, this compound readily releases formaldehyde, which is then involved in selective enzymatic transformations, giving rise either (i) to DHA using a formolase (FLS) catalysis or (ii) to l-erythrulose with a cascade reaction combining FLS and d-fructose-6-phosphate aldolase (FSA) A129S variant. Finally, the nature of the synthesized products is noteworthy, since carbohydrates are of high interest for the chemical and pharmaceutical industries. The present results prove that the cell-free synthesis of carbohydrates from CO as a sustainable carbon source is a possible alternative pathway in addition to the intensely studied biomass extraction and syntheses from fossil resources.