Kinetic and Dynamic Kinetic Resolution of Secondary Alcohols with Ionic-Surfactant-Coated Burkholderia cepacia Lipase: Substrate Scope and Enantioselectivity

Lipase Immobilized on MCFs as Biocatalysts for Kinetic and Dynamic Kinetic Resolution of sec-Alcohols

Dynamic kinetic resolution (DKR) is one of the most attractive methods for enantioselective synthesis. In the reported studies, lipase B from Candida antarctica (CALB) immobilized on siliceous mesoporous cellular foams (MCF) functionalized with different hydrophobic groups, and two ruthenium complexes with substituted cyclopentadienyl ligands were investigated as catalysts for the chemoenzymatic DKR of (rac)-1-phenylethanol, using Novozym 435 as a benchmark biocatalyst. Studies on the (rac)-1-phenylethanol transesterification reaction showed that CALB supported on MCFs grafted with methyl groups is a promising biocatalyst and isopropenyl acetate is a preferable acylation agent. Both Ru-complexes activated by K3PO4 or t-BuOK, proved to be effective catalysts of the racemization reaction. The final DKR experiments using all catalysts combinations singled out, gave 96% conversion, and (R)-1-phenylethyl acetate enantiomeric excess of 98% in 8 h using K3PO4 activator.

Artificial Nanometalloenzymes for Cooperative Tandem Catalysis

Artificial metalloenzymes that combine the advantages of natural enzymes and metal catalysts have been getting more attention in research. As a proof of concept, an artificial nanometalloenzyme (CALB-Shvo@MiMBN) was prepared by co-encapsulation of metallo-organic catalyst and enzyme in a soft nanocomposite consisting of 2-methylimidazole, metal ions, and biosurfactant in mild reaction conditions using a one-pot self-assembly method. The artificial nanometalloenzyme with lipase acted as the core, and the metallo-organic catalyst embedded in micropore exhibited a spherical structure of 30-50 nm in diameter. The artificial nanometalloenzyme showed high catalytic efficiency in the dynamic kinetic resolution of racemic primary amines or secondary alcohols compared to the one-pot catalytic reaction of immobilized lipase and free metallo-organic catalyst. This artificial nanometalloenzyme holds great promise for integrated enzymatic and heterogeneous catalysis.

Burkholderia cepacia lipase immobilization for hydrolytic reactions and the kinetic resolution of the non-equimolar mixtures of isomeric alcohols

The major drawbacks of native lipase applications in processes occurring in water or in organic solvents include: difficulties in catalyst recycling, low activity and operational instability. The immobilization of Burkholderia cepacia lipase by adsorption or covalent binding onto 5 differently functionalized carriers (silica, acrylic, cellulose-based) was performed to overcome this problem. The optimization of the reaction preparation in water-rich media was based on the hydrolytic reactivity of the preparations, as well as the thermal, operational and storage stabilities. Aminated silica carrier, activated with glutaraldehyde, was determined to be the carrier of choice. Regarding processes in water-restricted media, carrier selection was based on reactivity after drying and five preparations were chosen for the resolution of a non-equimolar isomer mixture (85:15 ratio of R to S isomers), treating the kinetic resolution of ((+)-(S/R)-1-[(1S,5R)-6,6-dimethylbicyclo[3.1.0]hex-2-en-2-yl)]ethanol as a model. The resulting acetate of R configuration exhibits interesting sensory properties. The operational stability of the chosen catalysts was tested over 15 consecutive batch processes; the most beneficial results were obtained with lipase adsorbed on an acrylic carrier. Conversion increased gradually from 10 to 84% over the first five processes, which could be explained by the product sorption onto the carrier. Full kinetic resolution with maximal substrate conversion (approximately 84%) was achieved and remained stable during the next 10 runs, an excellent result, and thus, the proposed system might be regarded as an exceptionally attractive solution for the perfume and cosmetic industries.

Lipases: An Overview

Lipases are ubiquitous enzymes, widespread in nature. They were first isolated from bacteria in the early nineteenth century, and the associated research continuously increased due to the characteristics of these enzymes. This chapter reviews the main sources, structural properties, and industrial applications of these highly studied enzymes.

Activation of Lipase-Catalyzed Reactions Using Ionic Liquids for Organic Synthesis

The use of ionic liquids to replace organic or aqueous solvents in biocatalysis processes has recently received great attention, and much progress has been made in this area; the lipase-catalyzed reactions are the most successful. Recent developments in the application of ionic liquids as solvents in lipase-catalyzed reactions for organic synthesis are reviewed, focusing on the ionic liquid mediated activation method of lipase-catalyzed reactions.

Ionic-surfactant-coated subtilisin: activity, enantioselectivity, and application to dynamic kinetic resolution of secondary alcohols

In this work, we explored the utility of ionic-surfactant-coated Bacillus licheniformis subtilisin (ISCBLS) as the catalyst for the dynamic kinetic resolution of secondary alcohols. ISCBLS was prepared by freeze-drying Bacillus licheniformis subtilisin with both ionic surfactant 1 and dextrin. ISCBCL displayed 9300-fold enhanced activity relative to its native counterpart in the transesterificaion of N-acetyl phenylalanine ethyl ester with 1-propanol in hexane and 12 800-fold enhanced activity in the transesterification of trifluoroethyl butyrate with 1-phenylethanol in THF. The enantioselectivity of ISCBLS was examined with 50 secondary alcohols as the substrates for kinetic resolution in the presence of trifluoroethyl butyrate. ISCBLS displayed synthetically useful enantioselectivity for most of the secondary alcohols tested. The enantioselectivity of ISCBLS was in particular good to high for m- or p-substituted 1-phenylethanols. The DKRs of these secondary alcohols by the combination of ISCBLS and a ruthenium-based racemization catalyst provided the products of (S)-configuration with good results (80-94% yield, 90-99% ee). It is concluded that ISCBLS is of great use as the enantiocomplementary counterpart of (R)-selective lipase for the dynamic kinetic resolution of secondary alcohols.

Spatial effects of oxovanadium-immobilized mesoporous silica on racemization of alcohols and application in lipase-catalyzed dynamic kinetic resolution

The nano-scale pores of mesoporous silica and their polar environment accelerate the racemization to make the lipase/oxovanadium combo-catalysed DKR applicable to a wider range of alcohols.

Molecular bioimprinting of lipases with surfactants and its functional consequences in low water media

Lipases from Thermomyces lanuginosa (TLL), Candida rugosa (CRL) and Burkholderia cepacia (BCL) were obtained in the 'open lid' form by adding surfactant molecules like n-octyl-β-d-glucopyranoside (OG), hexadecyl trimethyl ammonium bromide (CTAB), Bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) and triton X-100 for this purpose. The enzymes were 'dried' by precipitating with 4× (v/v) excess of organic solvents. The imprint surfactant molecules were removed by extensive washing with organic solvents. TLL imprinted with 0.05% CTAB showed 11-fold increase in the transesterification activity and was a better preparation to kinetically resolve (±)-1-phenylethanol. Fluorescence emission spectra confirmed that Trp89 of the lid was indeed affected during bioimprinting. With CRL, bioimprinting with OG gave 7-fold increase in the transesterification rates and resulted in reversal of enantioselectivity of CRL and gave R-phenylethyl acetate instead of the S-product as with the unimprinted precipitate. Bioimprinted BCL was also a 7-fold better catalyst for transesterification as well as enantioselectivity.

Chemoenzymatic dynamic kinetic resolution: a powerful tool for the preparation of enantiomerically pure alcohols and amines

Chemoenzymatic dynamic kinetic resolution (DKR) constitutes a convenient and efficient method to access enantiomerically pure alcohol and amine derivatives. This Perspective highlights the work carried out within this field during the past two decades and pinpoints important avenues for future research. First, the Perspective will summarize the more developed area of alcohol DKR, by delineating the way from the earliest proof-of-concept protocols to the current state-of-the-art systems that allows for the highly efficient and selective preparation of a wide range of enantiomerically pure alcohol derivatives. Thereafter, the Perspective will focus on the more challenging DKR of amines, by presenting the currently available homogeneous and heterogeneous methods and their respective limitations. In these two parts, significant attention will be dedicated to the design of efficient racemization methods as an important means of developing milder DKR protocols. In the final part of the Perspective, a brief overview of the research that has been devoted toward improving enzymes as biocatalysts is presented.