Lipase-catalyzed transformations with unnatural acyl acceptors

Biocatalysis and biomass conversion: enabling a circular economy

This paper is based on a lecture presented to the Royal Society in London on 24 June 2019. Two of the grand societal and technological challenges of the twenty-first century are the 'greening' of chemicals manufacture and the ongoing transition to a sustainable, carbon neutral economy based on renewable biomass as the raw material, a so-called bio-based economy. These challenges are motivated by the need to eliminate environmental degradation and mitigate climate change. In a bio-based economy, ideally waste biomass, particularly agricultural and forestry residues and food supply chain waste, are converted to liquid fuels, commodity chemicals and biopolymers using clean, catalytic processes. Biocatalysis has the right credentials to achieve this goal. Enzymes are biocompatible, biodegradable and essentially non-hazardous. Additionally, they are derived from inexpensive renewable resources which are readily available and not subject to the large price fluctuations which undermine the long-term commercial viability of scarce precious metal catalysts. Thanks to spectacular advances in molecular biology the landscape of biocatalysis has dramatically changed in the last two decades. Developments in (meta)genomics in combination with 'big data' analysis have revolutionized new enzyme discovery and developments in protein engineering by directed evolution have enabled dramatic improvements in their performance. These developments have their confluence in the bio-based circular economy. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Broadening the Scope of Biocatalysis in Sustainable Organic Synthesis

This Review is aimed at synthetic organic chemists who may be familiar with organometallic catalysis but have no experience with biocatalysis, and seeks to provide an answer to the perennial question: if it is so attractive, why wasn't it extensively used in the past? The development of biocatalysis in industrial organic synthesis is traced from the middle of the last century. Advances in molecular biology in the last two decades, in particular genome sequencing, gene synthesis and directed evolution of proteins, have enabled remarkable improvements in scope and substantially reduced biocatalyst development times and cost contributions. Additionally, improvements in biocatalyst recovery and reuse have been facilitated by developments in enzyme immobilization technologies. Biocatalysis has become eminently competitive with chemocatalysis and the biocatalytic production of important pharmaceutical intermediates, such as enantiopure alcohols and amines, has become mainstream organic synthesis. The synthetic space of biocatalysis has significantly expanded and is currently being extended even further to include new-to-nature biocatalytic reactions.

Dimethyl carbonate as a non-innocent benign solvent for the multistep continuous flow synthesis of amino alcohols

An efficient methodology for the production and resolution of amino alcohols with a low environmental impact has been developed.

First report on bio-catalytic N-formylation of amines using ethyl formate

A bio-catalyzed N-formylation reaction of different amines has been developed using ethyl formate as a formylating agent.

Applications of Liquid/Liquid Biphasic Oxidations by Hydrogen Peroxide with Ionic Liquids or Deep Eutectic Solvents

This Minireview focuses on recent applications of ionic liquids (ILs) and deep eutectic solvents (DESs) in biphasic oxidations in which the oxidizing agent corresponds to hydrogen peroxide. Biphasic reactions are accomplished when the substrate presents low or moderate solubility in aqueous (polar) systems and/or when separation of products and byproduct is an issue. The properties of the IL and DES allows the reaction activity to be intensified. On the other hand, the high chemical stability of the ionic solvents allows the use of hydrogen peroxide to minimize solvent degradation and unwanted byproducts. The experimental evidence presented herein shows that ILs and DESs can be used as cocatalysts, catalysts, and solvents to achieve enhanced yields and conversions. The process advantages, in terms of a reduction of volatile solvents, improve the safety and use of the oxidizing agent, which implies the possibility of developing new process improvements in the future.

Use of insoluble yeast β-glucan as a support for immobilization of Candida rugosa lipase

In the present study, insoluble yeast beta-glucan (IYG) has been explored as a support matrix for enzyme immobilization. IYG contains mainly beta-(1-3) linkages along with some intra- or inter-molecular branches of beta-(1-6) linkages with large number of free hydroxyl groups. Epichlorohydrin was used to convert these free hydroxyl groups into activated epoxy groups that are capable of forming covalent linkages with various groups of enzyme molecule. The epoxy-activated IYG was evaluated for immobilization of Candida rugosa lipase (CRL). Post-immobilization treatment of 5% glutaraldehyde was given in order to achieve stable and irreversible binding of enzyme on the support. The resultant biocatalytic IYG support expressed lipase activity of 8136.7 U/g and 59.6% activity yield. There was 51.05% retention of synthetic activity after six repeated esterification cycles, indicating its stability and reusability in non-aqueous medium. Moreover, the immobilized lipase gave the storage half-life of about 285 days (at 4 degrees C).

Solvent-free enzymatic synthesis of fatty alkanolamides

An environmentally benign and volume efficient process for enzymatic production of alkanolamides is described. Immobilized Candida antarctica lipase B, Novozym435, was used to catalyze the condensation of lauric acid with monoethanolamine. The reaction temperature of 90 degrees C was required to keep the reactants in a liquid state. Stepwise addition of the amine minimized problems caused by the formation of a highly viscous amine/fatty acid ion-pair. The enzyme was both very active and stable under the reaction conditions, with about half of the activity remaining after 2 weeks. The maximum amide yield obtained when using equimolar amounts of the reactants was 75%, which could be increased to 95% upon water removal. Special precautions to avoid co-distillation of the amine were required. Two different strategies to avoid the amine loss are presented.

Hydrolase-catalysed synthesis of peroxycarboxylic acids: Biocatalytic promiscuity for practical applications

The enzymatic promiscuity concept involves the possibility that one active site of an enzyme can catalyse several different chemical transformations. A rational understanding of the mechanistic reasons for this catalytic performance could lead to new practical applications. The capability of certain hydrolases to perform the perhydrolysis was described more than a decade ago, and recently its molecular basis has been elucidated. Remarkably, a similarity between perhydrolases (cofactor-free haloperoxidases) and serine hydrolases was found, with both groups of enzymes sharing a common catalytic triad, which suggests an evolution from a common ancestor. On the other hand, several biotechnological applications derived from the capability of hydrolases to catalyse the synthesis of peracids have been reported: the use of hydrolases as bleaching agents via in situ generation of peracids; (self)-epoxidation of unsaturated fatty acids, olefins, or plant oils, via Prileshajev epoxidation; Baeyer-Villiger reactions. In the present review, the molecular basis for this promiscuous hydrolase capability, as well as identified applications are reviewed and described in detail.

Substrate specificity of lipases in alkoxycarbonylation reaction: QSAR model development and experimental validation

Although lipases are known to catalyze alkoxycarbonylation reactions in organic solvents, the existing knowledge base on their substrate specificity in alkoxycarbonylation reaction is sparse. Moreover, models to predict substrate specificity have not been reported. Here, we report the experimentally measured rate constants for 180 acyl donor-alcohol pairs and demonstrate the two-step synthesis of over 70 disubstituted carbonate products from simple precursors such as diphenyl carbonate and alcohols. The efficiency of synthesis was found to be dependent on the order of alcohol addition. This motivated the need to develop a model to predict lipase specificity in alkoxycarbonylation reactions. A partial least square model has been developed to correlate the reaction rate with (i) descriptors of alcohol for a fixed acyl donor, (ii) descriptors of acyl donor for a fixed alcohol, (iii) descriptors of both the acyl donor and the alcohol. The number of descriptors being far greater than the number of observations was a potential limitation in the model development. This was addressed by selecting a subset of descriptors using a systematic procedure based on (a) correlation among the descriptors and step-wise regression methodology, and (b) variable influence on projection methodology. The model was able to accurately predict the reaction rate and the optimal order of addition of alcohols in the two-step synthesis of disubstituted carbonates using the enzyme mixture. The descriptor subset and the relevant model would benefit the users of lipases in synthetic applications while the modeling strategy presented here can have applications in predicting specificity of other enzymes.

Novel microbial lipases: catalytic activity in reactions in organic media

2,000 microbial strains were isolated from soil samples and tested to determine their lipolytic activity by employing screening techniques on solid and in liquid media. Culture broths were initially tested with 1,2-O-dilauryl-rac-glycero-3-glutaric acid-resorufinyl ester, a chromogenic substrate specific for lipases. Fourteen lipase-producing microorganisms were selected and their taxonomic identification was carried out. Hydrolysis of tributyrin or olive oil and the esterification of oleic acid with heptanol were selected to preliminary evaluate the catalytic activity of these lipases. All the selected lipases catalysed this esterification reaction with good yields. Resolution of (R,S)-2-(4-isobutylphenyl) propionic acid, (R,S)-1-phenylethanol, (R,S) 1-phenylethylamine and of (R) or (S) glycidol were performed to evaluate the stereoselectivity of these novel enzymes as biocatalysts in reactions in organic media. Lipases from the fungi Fusarium oxysporum and Ovadendron sulphureo-ochraceum gave the best yields and enantioselectivities in the resolution of racemic ibuprofen and 1-phenylethanol. Several lipases displayed a high stereoselectivity in the resolution of chiral amines by an alcoxycarbonylation reaction.

Lipase and esterase-catalyzed acylation of hetero-substituted nitrogen nucleophiles in water and organic solvents

The lipase- and esterase-catalyzed acylations of hydroxylamine and hydrazine derivatives with octanoic acid and ethyl octanoate are described. The influence of solvent and nucleophile on the initial reaction rate was investigated for a number of free and immobilized enzymes. Initial rates were highest in water, but the overall productivity was optimal in dioxane. Octanoic acid (250 g/L) was converted for 93% into the hydroxamic acid in 36 h with only 1% (w/w) Candida antarctica lipase B (Novozym 435) in dioxane at 40 degrees C. This translates to a catalyst productivity of 68.5 g. g(-1). day(-1) and a space time yield of 149 g. L(-1). day(-1), unprecedented figures in the direct reaction of an acid with a nitrogen nucleophile in an organic solvent.

Enzymatic synthesis of carbonate monomers and polycarbonates

Diphenyl carbonate is an attractive monomer for copolymerization with Bisphenol-A to produce the strong, high melting polycarbonate, Bisphenol-A Polycarbonate. Diphenyl carbonate is an ideal candidate for this polymerization as the phenols constitute good leaving groups during polymerization. Industrially, diphenyl carbonate is produced via the phosgenation of a phenolic sodium salt. Using phosgene creates additional safety hazards as well as concerns in treating or disposing of the reaction by-products. The enzymatic synthesis of diphenyl carbonate via alcoholysis of dimethyl carbonate by phenol is presented. While the process is environmentally benign and eliminates the considerable safety issues related to the use of phosgene, phenol is a poor nucleophile and conversion to diphenyl carbonate is limited. Enzyme catalyzed condensation polymerization of carbonate monomers and diols is a more feasible and direct enzymatic route to polycarbonate. We describe an AA-BB condensation polymerization to make polycarbonates using enzymes at ambient conditions. Molecular weights of up to 8, 500 MW are achieved. Unlike the industrial polymerization, this process is performed without the use of acid catalysts, significant energy input, or high temperature or pressure.