The potential of converting carbon dioxide to food compounds via asymmetric catalysis

Abstract

The food crisis caused by diminished arable land, extreme weather and climate change linked to increased carbon dioxide (CO₂) emission, is threatening global population growth. Interestingly, CO₂, the most widespread carbon source, can be converted into food ingredients. Here, we briefly discuss the progress and challenges in catalytic conversion of CO₂ to food ingredients via chiral catalysis.

Fig. 1. Schematic illustration of an artificial synthesis system for glucose. CO₂ was first converted to acetic acid through a two-step electrochemical reaction. The generated acetic acid was then fermented in a bioreactor as a microbial substrate to produce long-chain compounds such as glucose (ref. 2).

Fig. 2. Design of an artificial starch anabolic pathway (ASAP) system that converts CO₂ to starch. CO₂ is first reduced to one-carbon units (C1), such as methanol. Then, methanol is oxidized to formaldehyde (FADH). FADH is treated with formolase (FLS) to produce dihydroxyacetone (DHA). Then, DHA is phosphorylated to form dihydroxyacetone phosphate (DHAP). DHAP is treated with triose phosphate isomerase (TPI) to from d-glyceraldehyde 3-phosphate (GAP). So far, the synthesis of three-carbon units (C3) has been completed. Next, GAP is treated with (FBA) to form d-fructose-1,6-bisphosphate (F-1,6-BP). Then, F-1,6-BP is treated with fructose-bisphosphatase (FBP) to form d-fructose-6-phosphate (F-6-P). F-6-P is then treated with phosphoglucose isomerase (PGI) to form d-glucose-6-phosphate (G-6-P). The presence of G-6-P implies the successful preparation of six-carbon units (C6). After that, G-6-P is treated with phosphoglucomutase (PGM) to form d-glucose-1-phosphate (G-1-P). Then, G-1-P is treated with ADP-glucose pyrophosphorylase to form ADP glucose (ADPG). ADPG then is treated with starch synthase (SS) to form starch. This is the final composite module (Cn) of the ASAP system (ref. 3).

Fig. 3. Strategies for direct catalytic conversion of CO₂ into chiral intermediates. Asymmetric C–O bond formation with CO₂via kinetic resolution (a) or nucleophiles (b) (ref. 4). (c and d) Chiral metal complex and nucleophile co-catalyzed kinetic resolution of racemic epoxides with CO₂ to form chiral cyclic carbonates and polycarbonates (ref. 4).

Fig. 4. (a) Domino reactions involving Pd or Ir-catalyzed allylation reaction (ref. 23). (b) Transition-metal-catalyzed allylation of allyl carbonates with amines (ref. 24).

Fig. 5. (a) Asymmetric C–C bond formation with CO₂ (ref. 4). (b) Strategies for enantioselective C–H functionalization (ref. 25).

Fig. 6. Strategies for direct catalytic conversion of CO₂ into chiral α-amino acids (ref. 4).