Effect of different reaction parameters on the lipase-catalyzed selective acylation of polyhydroxylated natural compounds in ionic liquids

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Continuous Flow Glycolipid Synthesis Using a Packed Bed Reactor

Glycolipids are a class of biodegradable biosurfactants that are non-toxic and based on renewables, making them a sustainable alternative to petrochemical surfactants. Enzymatic synthesis allows a tailor-made production of these versatile compounds using sugar and fatty acid building blocks with rationalized structures for targeted applications. Therefore, glycolipids can be comprehensively designed to outcompete conventional surfactants regarding their physicochemical properties. However, enzymatic glycolipid processes are struggling with both sugars and fatty acid solubilities in reaction media. Thus, continuous flow processes represent a powerful tool in designing efficient syntheses of sugar esters. In this study, a continuous enzymatic glycolipid production catalyzed by Novozyme 435® is presented as an unprecedented concept. A biphasic aqueous–organic system was investigated, allowing for the simultaneous solubilization of sugars and fatty acids. Owing to phase separation, the remaining non-acylated glucose was easily separated from the product stream and was refed to the reactor forming a closed-loop system. Productivity in the continuous process was higher compared to a batch one, with space–time yields of up to 1228 ± 65 µmol/L/h. A temperature of 70 °C resulted in the highest glucose-6-O-decanoate concentration in the Packed Bed Reactor (PBR). Consequently, the design of a continuous biocatalytic production is a step towards a more competitive glycolipid synthesis in the aim for industrialization.

Improved Productivity of Naringin Oleate with Flavonoid and Fatty Acid by Efficient Enzymatic Esterification

Naringin is a flavonoid found in citrus fruits. It exhibits biological activities, such as anticancer and antioxidant effects, but it suffers from low solubility and low stability in lipophilic systems. These drawbacks lead to difficulties in the commercial application of naringin, but they can be overcome through esterification. In this study, naringin oleate was synthesized by enzymatic esterification and optimal conditions for the reaction were investigated. Experiments were conducted focusing on the following parameters: enzyme type, enzyme concentration, molar ratio of naringin to oleic acid, reaction temperature, and reaction solvent. We further confirmed the degree of esterification based on the difference in the initial and the final naringin concentrations. A conversion of 93.10% was obtained under optimized conditions (Lipozyme TL IM 10 g/L, molar ratio 1:20, reaction temperature 40 °C, acetonitrile as solvent, and 48 h reaction time). Thus, naringin oleate, a high value-added material that overcomes the low hydrophobicity of naringin and enhances its performance, was obtained through esterification of naringin using oleic acid. This study presented a method for the efficient enzymatic synthesis that could ensure high conversion within a shorter reaction time compared with that required in previously reported methods.

Ionic Liquid-Like Pharmaceutical Ingredients and Applications of Ionic Liquids in Medicinal Chemistry: Development, Status and Prospects

Background:

As a new kind of green media and bioactive compounds with special structure, Ionic Liquids (ILs) are attracting much attention and applied widely in many fields. However, their roles and potential have not been fully recognized by many researchers of medicinal chemistry. Because of obvious differences from other traditional drugs and reagents, their uses and performance together with advantages and disadvantages need to be explored and reviewed in detail.

Methods:

For a systematic and explicit description of the relationship between ILs and medicinal chemistry, all of the contents were elucidated and summarized in a series of independent parts. In each part, it started from the research background or a conceptual framework and then specific examples were introduced to illustrate the theme. Finally, the important conclusions were drawn and its future was outlooked after the discussion about related key problems appearing in each mentioned research. Meanwhile, methodologies such as empirical analysis, comparison and induction were applied in different sections to exposit our subject.

Results:

The whole review was composed of five parts, and 148 papers were cited in total. Related basic information of ionic liquids was provided on the basis of representative references, including their concepts and important characters. Then 82 papers outlined ionic liquid-like active pharmaceutical ingredients, which unfolded with their major biological activities (antimicrobial activity, antibiofilm activity, antitumor activity, anticholinesterase activity and so on). Applications of ionic liquids in the synthesis of drugs and pharmaceutical intermediates were elaborated in 92 papers to illustrate the important roles of ILs and their extraordinary properties in this field. Moreover, new technologies (such as immobilization of IL, microwave reaction, solventfree synthesis, microreactor, etc) were introduced for further innovation. Finally, 26 papers were included to expound the status of the IL-assisted derivatization of various natural lead compounds.

Conclusion:

This review placed emphasis on chemical structures of ILs and their structureactivity relationships in a specific manner, leading to meaningful and valuable related information to some related fields and thus promotes further development and application of various ILs for medicinal chemistry. The deep exploration for key scientific problems is the driving force to propel their theoretical breakthrough and industrial production.

The modulatory effect and the mechanism of flavonoids on obesity

With the improvement of living standards, obesity has become a serious health problem all over the word. Currently, the methods and drugs for obesity treatment have some limitations and side effects. Flavonoids are active constituents with various biological activities, widely found in plants, and numerous studies have shown that flavonoids can inhibit obesity and related metabolism disorders effectively. This perspective reviews the recent progress in understanding the anti-obesity effects of flavonoids through modulating food intake, enzyme activities, nutrition absorption, adipogenesis and adipocyte lifecycle, thermogenesis, energy consumption, and intestinal microbiota. PRACTICAL APPLICATIONS: Natural bioactive substance flavonoids have anti-obesity property, which may play a role in anti-obesity drugs or functional food without any side effects. Flavonoids can inhibit weight gain directly or through their biologically active metabolites by various potential pathways. A better understanding of the modulatory effect and the mechanism of flavonoids on obesity will allow us to better utilize flavonoids in plants to treat obesity and related metabolic syndrome.

Tailoring naringenin conjugates with amplified and triple antiplatelet activity profile: Rational design, synthesis, human plasma stability and in vitro evaluation

BACKGROUND

The current standard-of-care antiplatelet therapy in cardiovascular disease patients is consisted of cyclooxygenase-1 (COX-1) inhibitor aspirin, along with a platelet receptor P2Y₁₂ antagonist. Recently, the triple antiplatelet therapy with aspirin, a P2Y₁₂ receptor antagonist and a protease activated receptor-1 (PAR-1) antagonist, has been suggested for the secondary prevention of atherothrombotic events, however presented an increased risk of bleeding. Therefore, the quest for novel antiplatelet agents simultaneously targeting the three pathways with improved efficacy/safety profile is of immense importance. Flavonoids as pre-validated ligands for numerous targets could serve as scaffolds targeting the three platelet activation pathways.

METHODS

Computational methods, Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) plasma stability and in vitro platelet aggregation experiments were used to establish the antiplatelet activity of the flavonoid naringenin and its conjugates.

RESULTS

In silico studies indicated that naringenin could bear a potent triple antiplatelet activity by inhibiting different platelet aggregation mechanisms. However, we found that in human platelets naringenin has diminished activity. We rationally designed and synthesized different naringenin conjugates aiming to amplify the antiplatelet activity of the parent compound. UHPLC-MS/MS revealed a slow degradation rate for a docosahexaenoic acid (DHA) - naringenin conjugate in human plasma. The antiplatelet profile of the new analogues was evaluated against in vitro platelet aggregation induced by several platelet agonists.

CONCLUSIONS

The DHA - naringenin hybrid presented triple antiplatelet activity simultaneously targeting PAR-1, P2Y₁₂ and COX-1 platelet activation pathways.

GENERAL SIGNIFICANCE

Natural products could offer a rich source for novel bioactives as a powerful alternative to the current combinatorial use of three different antiplatelet drugs.

Enzymatic Synthesis of Glucose-Based Fatty Acid Esters in Bisolvent Systems Containing Ionic Liquids or Deep Eutectic Solvents

Sugar fatty acid esters (SFAEs) are biocompatible nonionic surfactants with broad applications in food, cosmetic, and pharmaceutical industries. They can be synthesized enzymatically with many advantages over their chemical synthesis. In this study, SFAE synthesis was investigated by using two reactions: (1) transesterification of glucose with fatty acid vinyl esters and (2) esterification of methyl glucoside with fatty acids, catalyzed by Lipozyme TLIM and Novozym 435 respectively. Fourteen ionic liquids (ILs) and 14 deep eutectic solvents (DESs) were screened as solvents, and the bisolvent system composed of 1-hexyl-3-methylimidazolium trifluoromethylsulfonate ([HMIm][TfO]) and 2-methyl-2-butanol (2M2B) was the best for both reactions, yielding optimal productivities (769.6 and 397.5 µmol/h/g, respectively) which are superior to those reported in the literature. Impacts of different reaction conditions were studied for both reactions. Response surface methodology (RSM) was employed to optimize the transesterification reaction. Results also demonstrated that as co-substrate, methyl glucoside yielded higher conversions than glucose, and that conversions increased with an increase in the chain length of the fatty acid moieties. DESs were poor solvents for the above reactions presumably due to their high viscosity and high polarity.

Enzymatic synthesis of bioactive compounds with high potential for cosmeceutical application

Cosmeceuticals are cosmetic products containing biologically active ingredients purporting to offer a pharmaceutical therapeutic benefit. The active ingredients can be extracted and purified from natural sources (botanicals, herbal extracts, or animals) but can also be obtained biotechnologically by fermentation and cell cultures or by enzymatic synthesis and modification of natural compounds. A cosmeceutical ingredient should possess an attractive property such as anti-oxidant, anti-inflammatory, skin whitening, anti-aging, anti-wrinkling, or photoprotective activity, among others. During the past years, there has been an increased interest on the enzymatic synthesis of bioactive esters and glycosides based on (trans)esterification, (trans)glycosylation, or oxidation reactions. Natural bioactive compounds with exceptional theurapeutic properties and low toxicity may offer a new insight into the design and development of potent and beneficial cosmetics. This review gives an overview of the enzymatic modifications which are performed currently for the synthesis of products with attractive properties for the cosmeceutical industry.

Efficient mono-acylation of fructose by lipase-catalyzed esterification in ionic liquid co-solvents

Fructose monoesters are eco-friendly nonionic surfactants in various applications. Selective preparation of mono-acylated fructose is challenging due to the multiple hydroxyl sites available for acylation both chemically and enzymatically. Ionic liquids (ILs) have profound impacts not only on the reaction media but also on the catalytic properties of enzymes in the acylation process. In this study, utilizing an IL co-solvent system, selective synthesis of mono-acylated fructose with lauric acid catalyzed by immobilized Candida antarctica lipase B (CALB) was investigated. The imidazolium-based ILs selected as co-solvents with 2-methyl-2-butanol (2M2B) markedly improved the ratios of monolauroyl fructose in the presence of 60% [BMIM][TfO] (v/v) and 20% [BMIM][BF4] (v/v), in which the mono-acylated fructose was 85% and 78% respectively. Based on a Ping-Pong Bi-Bi model, a kinetic equation was fitted, by which the kinetic parameters revealed that the affinity between fructose and acyl-enzyme intermediate was enhanced. The inhibition effect of fructose on free enzyme was weakened in the presence of IL co-solvents. The conformation of CALB binding substrates also changed in the co-solvent system as demonstrated by Fourier transform infrared spectra. These results demonstrated that the variation of CALB kinetic characteristics was a crucial factor for the selectivity of mono-acylation in ILs/2M2B co-solvents.

A novel chemoenzymatic synthesis of propyl caffeate using lipase-catalyzed transesterification in ionic liquid

Propyl caffeate has the highest antioxidant capacity in the caffeate alkyl esters family, but industrial production of propyl caffeate is hindered by low yields using either the chemical or enzymatic catalysis method. To set up a high-yield process for obtaining propyl caffeate, a novel chemoenzymatic synthesis method using lipase-catalyzed transesterification of an intermediate methyl caffeate or ethyl caffeate and 1-propanol in ionic liquid was established. The maximum propyl caffeate yield of 98.5% was obtained using lipase-catalyzed transesterification under the following optimal conditions: Novozym 435 as a biocatalyst, [Bmim][CF3SO3] as a medium, a molar ratio of methyl caffeate to 1-propanol of 1:5, a mass ratio of methyl caffeate to lipase of 1:20, and a reaction temperature of 60°C. The two-step conversion of caffeic acid to propyl caffeate via methyl caffeate is an efficient way to prepare propyl caffeate with an overall yield of 82.7%.

Surface modification of magnetite nanoparticles using gluconic acid and their application in immobilized lipase

Superparamagnetic magnetite nanoparticles (SMN) were surface-modified with gluconic acid (GLA) to improve their hydrophilicity and bio-affinity. Gluconic acid was successfully coated on the surface of magnetite nanoparticles and characterized using Fourier transform infrared spectroscopy (FT-IR). With water-soluble carbodiimide (EDC) as the coupling reagent, lipase was successfully immobilized onto the hydroxyl-functionalized magnetic nanoparticles. The immobilized lipase had better resistance to temperature and pH inactivation in comparison to the free form and hence widened the reaction pH and temperature range. Thermostability and storage stability of the enzyme improved upon covalent immobilization. Immobilized lipase showed higher activity after recycling when compared to the free one and could be recovered by magnetic separation.

Identification of suitable ionic liquids for application in the enzymatic hydrolysis of rutin by an automated screening

An automated method in milliliter scale was developed for the screening of process parameters concerning the hydrolysis of the flavonoid rutin catalyzed by the rhamnosidase activity of naringinase from Penicillium decumbens. Besides the effect of additives such as ionic liquids and low molecular salts, the productivity in a multiple phase system as well as the recyclability of the enzyme in repetitive batches were studied. The hydrophobic ionic liquid (IL) trihexyl(tetradecyl)phosphonium bis(trifluormethylsulfonyl)imide [P(h(3))t][Tf(2)N] was identified to combine the most favorable characteristics out of 23 investigated ILs with regard to enzyme compatibility, substrate solubility and enzyme partition coefficient. Also, for the corresponding cations 1-ethyl-3-methylimidazolium [EMIM], 1-butyl-3-methylimidazolium [BMIM], 1-butyl-1-methylpyrrolidinium [BMPL] and 1-octyl-3-methylimidazolium [OMIM], the entity with the [Tf(2)N] anion was best tolerated by the naringinase. With increasing IL content, higher space time yields with up to 1.5 g/(L h) for 80% (v/v) [P(h(3))t][Tf(2)N] were achieved. Enhanced specific enzyme activity was observed in the presence of Ca(2+) ions. By addition of [P(h(3))t][Tf(2)N] and calcium chloride, the reactive aqueous phase was successfully used in three repetitive batches with full conversion.

Lipase-catalyzed esterification of ferulic Acid with oleyl alcohol in ionic liquid/isooctane binary systems

Lipase-catalyzed synthesis of ferulic acid oleyl alcohol ester in an ionic liquid (IL)/isooctane system was investigated. Considerable bioconversion and volumetric productivity were achieved in inexpensive 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF(6)]) and 1-methyl-3-octylimidazolium hexafluorophosphate ([Omim][PF(6)]) mediated systems, and thus, the two types of ILs were selected for further optimization of variables. The results showed that, before reaching a maximum, the increase of ferulic acid concentration, temperature, or enzyme dosage led to an increase in volumetric productivity. Variations of the ratios of IL/isooctane and concentrations of oleyl alcohol also profoundly affected the volumetric productivity. To a higher extent, [Hmim][PF(6)]/isooctane and [Omim][PF(6)]/isooctane show similar reaction behaviors. Under the optimized reaction conditions (60 °C, 150 mg of Novozym 435 and 100 mg of molecular sieves), up to 48.50 mg/mL productivity of oleyl feruleate could be achieved for the [Hmim][PF(6)]/isooctane (0.5 mL/1.5 mL) system with a substrate concentration of ferulic acid of 0.08 mmol/mL and oleyl alcohol of 0.32 mmol; while an optimum volumetric productivity of 26.92 mg/mL was obtained for the [Omim][PF(6)]/ isooctane (0.5 mL/1.5 mL) system under a similar reaction condition other than the substrate concentrations of ferulic acid at 0.05 mmol/mL and oleyl alcohol at 0.20 mmol.

Toward advanced ionic liquids. Polar, enzyme-friendly solvents for biocatalysis

Ionic liquids, also called molten salts, are mixtures of cations and anions that melt below 100 °C. Typical ionic liquids are dialkylimidazolium cations with weakly coordinating anions such as [MeOSO₃] or [PF₆]. Advanced ionic liquids such as choline citrate have biodegradable, less expensive and less toxic anions and cations. Deep eutectic solvents are also included in the advanced ionic liquids. Deep eutectic solvents are mixtures of salts such as choline chloride and uncharged hydrogen bond donors such as urea, oxalic acid, or glycerol. For example, a mixture of choline chloride and urea in 1:2 molar ratio liquifies to form a deep eutectic solvent. Their properties are similar to those of ionic liquids. Water-miscible ionic liquids as cosolvents with water enhance the solubility of substrates or products. Although traditional water-miscible organic solvents also enhance solubility, they often inactivate enzymes, while ionic liquids do not. The enhanced solubility of substrates can increase the rate of reaction and often increases the regio- or enantioselectivity. Ionic liquids can also be solvents for non-aqueous reactions. In these cases, they are especially suited to dissolve polar substrates. Polar organic solvent alternatives inactivate enzymes, but ionic liquids do not even when they have similar polarities. Besides their solubility properties, ionic liquids and deep eutectic solvents may be greener than organic solvents because ionic liquids are non-volatile and can be made from non-toxic components. This review covers selected examples of enzyme catalyzed reaction ionic liquids that demonstrate their advantages and unique properties and point out opportunities for new applications. Most examples involve hydrolases, but oxidoreductases and even whole cell reactions have been reported in ionic liquids.