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Michael addition is an important reaction to form C–C bonds. Different hydrolases (e.g., lipases, proteases, and D-aminoacylase) have been reported to catalyze C–C forming reactions, but the reaction mechanism is not entirely clear. This study examined several model Michael reactions catalyzed by lipases and amino acids in various solvents, and found that “‘water-like”’ functionalized ionic liquids (ILs) increased the reaction yield to 35-55% from 30% in triglyme and 17% in [BMIM][Tf2N]. Interestingly, tertiary amides as solvents remarkably increased the reaction yield (to up to 65–85%) and enantioselectivity (up to 71–84% ee) when catalyzed by porcine pancreatic lipase (PPL). Our experimental, spectroscopic, and computational studies discovered that the lipase catalysis can be attributed to basic amino acid residues as the catalysts to promote Michael addition, especially when tertiary amide solvents partially unfold the protein and expose its basic amino acid residues.
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Enzymatic Knoevenagel condensation in dual‐functionalized water‐mimicking ionic liquids and tertiary amide solvents
Abstract BACKGROUNDKnoevenagel condensation is an important tool for building carbon–carbon (CC) bonds, especially when catalyzed by enzymes to enable a potentially high chemo‐, regio‐ and/or stereoselectivity. Although many Knoevenagel condensation reactions are carried out in aqueous solutions, insoluble hydrophobic substrates often lead to poor catalytic efficiencies. The use of water‐miscible organic solvents improves the substrate solubilization, but usually induces activity suppression or inactivation of enzymes. There is a great need to develop alternative solvents for both substrate dissolution and enzyme compatibility in CC bond formation reactions. RESULTSOur group previously developed dual‐functionalized water‐mimicking ionic liquids (ILs) for the activation and stabilization of hydrolases (e.g. lipase and protease). In the present study, we evaluated the Knoevenagel condensation of 4‐chlorobenzaldehyde with acetylacetone, and found that porcine pancreas lipase in water‐mimicking ILs carrying ammonium, imidazolium and benzimidazolium cations enabled higher reaction rates (up to 3.22 μmol min−1 g−1lipase) and better yields thantert‐butanol, glymes and [BMIM][Tf2N]. Interestingly, tertiary amide solvents such asN‐methyl‐2‐pyrrolidone (NMP),N,N‐dimethylformamide (DMF) andN,N‐dimethylacetamide (DMAc) led to 8.2‐ to 11.1‐fold increases in the initial rate (up to 35.66 μmol min−1 g−1lipase) when compared with dual‐functionalized ILs, which is likely due to some synergistic effect of these tertiary amides with the lipase. CONCLUSIONDual‐functionalized ILs based on ammonium, imidazolium and benzimidazolium cations improved Knoevenagel condensation reaction rates and yields when compared withtert‐butanol and glymes. Tertiary amides (NMP, DMF and DMAc) significantly increased the reaction rate. © 2024 The Authors.Journal of Chemical Technology and Biotechnologypublished by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
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- Award ID(s):
- 2244638
- PAR ID:
- 10495099
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Chemical Technology & Biotechnology
- Volume:
- 99
- Issue:
- 4
- ISSN:
- 0268-2575
- Format(s):
- Medium: X Size: p. 780-787
- Size(s):
- p. 780-787
- Sponsoring Org:
- National Science Foundation
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