Kinetic Resolution of (R,S)-2-Butanol Using Enzymatic Synthesis of Esters

Abstract

Kinetic resolution of (R,S)-2-butanol using enzymatic synthesis of esters has been studied. (R,S)-2-Butanol is commonly found as a racemic mixture, and the products of its esterification are racemic mixtures too. This work is of great significance in the field of the enzymatic kinetic resolution due to the little information found in literature about the resolution of (R,S)-2-butanol as pure compound. So, this article is a contribution about the enzymatic resolution of (R,S)-2-butanol. The reaction here studied is the esterification/transesterification of (R,S)-2-butanol in organic media (n-hexane) using as biocatalyst the lipase Novozym 435®. The main target of this study is to analyze the influence of certain variables in this reaction. Some of these variables are acyl donor (acids and esters), concentration of substrates, enzyme/substrate ratio, and temperature. The main conclusions of this study are the positive effect of higher substrates concentration (1.5 M) and larger amount of enzyme (13.8 g mol(-1) substrate) on kinetic resolution rate but not a very noticeable effect on enantiomeric excesses. The longer the carboxylic acid chain is, the better results are obtained. Besides to achieve a satisfactory kinetic resolution, it is recommendable to select reaction times (180 min) at which the highest substrate enantiomeric excess is reached (~60%). The temperature has not an appreciable influence on the resolution in the range studied (40-60 °C). When an ester (vinyl acetate) is used as acyl donor, the resolution shows better results than when using a carboxylic acid as acyl donor (ee(s) ~90% at 90 min). Moreover, Michaelis-Menten parameters, v(max) and K(M), were determined, 0.04 mol l(-1) min(-1) and 0.41 mol l(-1), respectively.

New Proton Nuclear Magnetic Resonance-Based Derivation for Quantification of Alkyl Esters Generated Using Biocatalysis

“…The extent of transesterification enhanced from butanol (≅70%) to pentanol (≅76%) and decreased in hexanol (≅63%) and octanol (≅55%). These observations differ from those reported by Romero et al, 26 wherein there was no noticeable influence on the esterification effect when propanol, butanol, hexanol, and octanol were used as acyl acceptors. In the case of the transesterification reaction employing methanol, methanolysis takes place between two immiscible liquids.…”

Quantum Mechanics/Molecular Mechanics Insights into the Enantioselectivity of the O-Acetylation of (R,S)-Propranolol Catalyzed by Candida antarctica Lipase B

“…Many lipase-catalyzed reactions are highly selective and can be performed under mild reaction conditions . Moreover, lipases are well-established catalysts in organic synthesis currently, because they are highly stable and active in organic solvents. − They can catalyze a number of biotransformations which involve carboxylic groups, such as esterification, transesterification, and aminolysis. ,− One of the most frequently studied lipase-catalyzed reactions is the enantioselective acylation of racemic amines and secondary alcohols in organic solvents using vinyl or ethyl acetate as an acyl donor. − Attempts to increase the rate and the enantioselectivity of these reactions have focused on the modulation of the catalytic properties of the enzyme using protein engineering (e.g., directed mutation or immobilization of the enzyme) and different organic solvents and acyl donors. ,, …”