Carboxylic Acid Reductase Can Catalyze Ester Synthesis in Aqueous Environments

Abstract

Most of the well‐known enzymes catalyzing esterification require the minimization of water or activated substrates for activity. This work reports a new reaction catalyzed by carboxylic acid reductase (CAR), an enzyme known to transform a broad spectrum of carboxylic acids into aldehydes, with the use of ATP, Mg2+, and NADPH as co‐substrates. When NADPH was replaced by a nucleophilic alcohol, CAR from Mycobacterium marinum can catalyze esterification under aqueous conditions at room temperature. Addition of imidazole, especially at pH 10.0, significantly enhanced ester production. In comparison to other esterification enzymes such as acyltransferase and lipase, CAR gave higher esterification yields in direct esterification under aqueous conditions. The scalability of CAR catalyzed esterification was demonstrated for the synthesis of cinoxate, an active ingredient in sunscreen. The CAR esterification offers a new method for green esterification under high water content conditions.

One-Step Biocatalytic Synthesis of Sustainable Surfactants Using Selective Amide Bond Formation

“…requiring imidazole as a catalyst. [19] Thus, we suggest that the selectivity is controlled by the intrinsic preference of acyl phosphates in water for amide over ester formation, which is documented in the literature. [32,33] In summary, this study demonstrates the versatility of CAR-A for one-step, selective amide bond formation under aqueous conditions by starting from otherwise challenging, multifunctional substrates.…”

“…To test this hypothesis, N-methylglucamine 1 was reacted with a number of carboxylic acids using our previously described truncated CAR-A construct derived from CARmm from Mycobacterium marinum. [28] Starting with 3-fluoro cinnamic acid, a previously described substrate of the enzyme, we observed full conversion to a single reaction product on both LC-MS and 19 F-NMR (Supporting Information (SI)). The use of 19 F-NMR as a detection method allowed us to investigate crude reaction mixtures for competing ester bond formation, which was not observed.…”

“…[28] Starting with 3-fluoro cinnamic acid, a previously described substrate of the enzyme, we observed full conversion to a single reaction product on both LC-MS and 19 F-NMR (Supporting Information (SI)). The use of 19 F-NMR as a detection method allowed us to investigate crude reaction mixtures for competing ester bond formation, which was not observed. Next, reaction of 1 with decanoic acid led to the target surfactant MEGA-10 (4, figure 2A) with over 99% conversion, as determined by RP-HPLC at a wavelength of 210 nm, using a commercial standard as a reference (SI).…”

“…Moreover, the alcohol nucleophile had to be provided in over 1000-fold excess concentrations. [19] Encouraged by these results, we were interested in the selective amide bond formation between acids and multifunctional compounds like amino polyols catalyzed by CAR-A, without any unwanted ester or amide-ester byproducts. CARs are particularly attractive for this approach because of their wide substrate scope, which includes fatty acids.…”

Lipase-catalyzed esterification in water enabled by nanomicelles. Applications to 1-pot multi-step sequences

“…11,12 Only earlier this year did a report appear, outside the food industry, 7,13 describing an enzyme-catalyzed ester synthesis in aqueous alcoholic media. 14…”