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.

Biocatalysis making waves in organic chemistry

“…[294][295][296] A particularly noteworthy approach is the application of CAR for the synthesis of esters in water. 297 While up to now limited to primary alcohols, it shows that the catalytic machinery or several enzymes might be suitable for ester synthesis in water.…”

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability

“…In addition to its use as starting precursors for hydroxylation, various PAs have just recently been shown to serve as substrates for a side activity of carboxylic acid reductase (CAR) from Mycobacterium marinum . CAR could be used to synthesize methyl cinnamate, methyl ferulate, methyl 4-hydroxyphenylacetate, and cinoxate (a commercial sunscreen ester formed from methoxycinnamic acid and 2-ethoxyethanol).…”

“…In addition to its use as starting precursors for hydroxylation, various PAs have just recently been shown to serve as substrates for a side activity of carboxylic acid reductase (CAR) from Mycobacterium marinum. 398 CAR could be used to synthesize methyl cinnamate, methyl ferulate, methyl 4hydroxyphenylacetate, and cinoxate (a commercial sunscreen ester formed from methoxycinnamic acid and 2-ethoxyethanol). Although yields of these compounds are rather low at this point, the esterification catalyzed by CAR can be conducted in aqueous environments, making the system attractive for future applications in metabolic engineering.…”

One‐Step Biocatalytic Synthesis of Sustainable Surfactants by Selective Amide Bond Formation**

“…A recent study showed that CARs are also capable of ester formation. However, significant amounts of imidazole catalyst and alcohol nucleophile concentrations of over 1000‐fold excess were required to observe ester formation [20] …”