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Lipase-Catalyzed Michael Addition in 'Water-like' Ionic Liquids and Tertiary Amides: What Is the Role of the Enzymes?
Hua Zhao1, Angira Roy2, Ashen Samaranayake2
1Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota 55108, United States.
Abstract:
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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