Deep Eutectic Solvents for Enzymatic Esterification of Racemic Menthol

Abstract

Enzymatic esterification is an effective route that can contribute for the separation of racemic (rac) mixtures and is thus of great importance for the pharmaceutical, food, and cosmetic industries. All the processes involved in this methodology should be environmentally friendly, biocompatible, fast, and cost-effective. The use of deep eutectic solvents (DESs) can comply with all these metrics. In this work, we report on the use of DESs in the enzymatic esterification of menthol, one of the largest traded flavors and aromas worldwide. Solid rac-menthol was mixed with solid lauric acid at different molar ratios, yielding a DES liquid at room temperature or slightly above. Rac-menthol and lauric acid were the DES components and also the esterification reaction substrates. The DES reacted promptly when Candida rugosa lipase was added, and the conversions of rac-menthol reached up to 44% after 3 h of reaction and an enantiomeric excess of the product of 62%. Enzyme activity was dependent on the molar ratio of the substrates as well as on the water activity in the DES. The use of DES combined with enzymes paves the way for efficient and more sustainable biocatalytic processes.

Investigating the Variation in Solvation Interactions of Choline Chloride-Based Deep Eutectic Solvents Formed Using Different Hydrogen Bond Donors

“…2,3 The resulting eutectic mixture possesses a melting point that is lower than that of the individual HBA and HBD components. 4,5 Ammonium, phosphonium, and imidazolium salts are common HBAs, while organic acids, alcohols, amides, amines, and carbohydrates form the majority of employed HBDs. 6,7 DESs often possess low melting points, tunable viscosities, and low vapor pressures and involve preparation methods that eliminate the use of organic solvents.…”

Deep Eutectic Solvents and Multicomponent Reactions: Two Convergent Items to Green Chemistry Strategies

“…Because of the biocompatibility of many DESs, some experiments have been developed using enzymes in esterification and trans‐esterification reactions. Enzymatic esterification of racemic menthol with lauric acid in the presence of Candida rugosa lipase (CRL)reached up to 44 % after 3 h of reaction and an enantiomeric excess of the ester of 62 % [135] (Scheme 15 ). Racemic menthol and lauric acid form in situ a DES that provides the separation of the mixture.…”

Natural deep eutectic solvents as performance additives for biocatalysis

“…The original work used enantiomerically pure (-) menthol, which was later extended in work by Paiva and coworkers to the kinetic resolution of rac-menthol. (Craveiro et al, 2019) This two-in-one approach has also been used with sugar-based DES for the synthesis of fatty acid esters of carbohydrates,(M. Pöhnlein et al, 2015;Siebenhaller et al, 2018;Siebenhaller et al, 2016) structured lipids, (Zeng, Qi, Xin, Yang, & Wang, 2015) -Insua et al, 2019) Glu-ChCl, on the one hand, serves as cosubstrate to promote the glucosedehydrogenase (GDH)-catalysed regeneration of NAD(P)H and as cosolvent to enable higher substrate loadings.…”