Current Organic Chemistry - Volume 21, Issue 2, 2017

In the last quarter century, immobilization of lipases has rapidly grown into a field of converging knowledge on material science, chemical engineering, biochemistry, etc. The majority of the cumulative work on lipase immobilization has been done on silica (Si) based supports. Researchers have investigated the effect of different Si architectures such as monolith, particles and aerogels on the properties of the immobilized lipase. These heterogenous catalysts have proved efficient in synthetic reactions such as biodiesel formation, where, unlike other supports, siliceous materials are able to resist nonaqueous media, providing stability and reusability. The use of numerous sources of this type of enzymes assures the universality of silica for lipase immobilization. This work summarizes the immobilization strategies and functionalization methods on siliceous materials that have provided a fundamental technology base to exploit the power of lipases as biocatalyts.

The esterification is well-established type of reaction in organic synthesis used for manufacturing various valuable esters used prevalently as ingredients of food, skincare products, pharmaceuticals and fuels. In recent decades biocatalytic synthetic routes based on using enzymes as catalysts have received a lot of attention in scientific researches and industry. Main advantages of enzymatic esterifications are high selectivity (regioselectivity and enantioselectivity), performing reaction at milder conditions (moderate temperature and atmospheric pressure) and the fact that enzymatically synthesized product gain label of natural product, which increases its market appeal. The purpose of this review is to point out the most important advances in lipase-catalyzed ester synthesis in nonconventional reaction media, with special focus on several most important types of ester. This part of review starts with outcomes in synthesis of aroma esters, usually obtained using monofunctional aliphatic alcohols and acids, which have been investigated for decades and industrial processes are already established. However, later sections are dedicated to enzymatic esterification of more complex molecules (carbohydrates, vitamin C, flavonoids) having more than one functional groups, which are subject of numerous studies in recent times because in these reactions regioselectivity of biocatalysts can be fully explored and processes are still subject of optimization, especially with respect to selection of reaction media and media engineering.

The use of enzymes in food processing represents a historically well-established approach that gets its deepest roots in thousands of years BC. In fact, even in an unconscious way, the mankind always applied enzyme- based bioprocesses for example in beer brewing, bread baking, and cheese and wine making. Nevertheless, throughout the centuries, process improvement or design and implementation of novel approaches has been consistently performed, and especially in recent years, significant advances in protein engineering and biocatalyst design have been achieved and applied in food sector. Consequently, an updated overview regarding the applications of enzymes in the food sector and of progresses made, namely, within the scope of obtainment of more efficient biocatalysts through structural modification, protein engineering and immobilization of enzymes will be provided. The main scope of targeted improvements deal with the technological aspects related to the most representative strategies to achieve enzymes with enhanced thermal and operational stability, improved specific activity, modification of pH-activity profiles, and increased product specificity, among others.

Due to their physiological and functional properties, novel fructooligosaccharide (FOSs) and levan production has gained significant interest. Levansucrase (EC 2.4.1.10, LS), a glycosyl transferase, catalyzes the transfer of fructose from a non-activated sucrose donor, to an acceptor molecule, typically via a β-(2-6)-glycosidic bond. Significant prebiotic products of LS-catalyzed transfructosylation reaction include β-(2-6)-levans, neo-type FOSs, levan-type FOSs and heterofructooligosaccharides. The LS reaction/product profile consists of four reactions: exchange (sucrose), hydrolysis (glucose and fructose), oligomerization (FOSs) and polymerization (levan). Within the context of this review, the catalytic efficiency and the reaction specificity (transfructosylating versus hydrolytic) of LS was discussed as function of the enzyme’s structure and the reaction conditions. The acceptor specificity of LSs, leading to the synthesis of heterofructooligosaccharides, was also examined. With the purpose of increased enzymatic stability, reusability, advanced levan/FOS production, the immobilization of LS was discussed.

Cyclodextrins are cyclic oligosaccharides constituted by glucopyranose units linked by -(1,4) bonds that show a characteristic donut shape with a hydrophobic cavity and a hydrophilic outer surface. Cyclodextrins are capable of forming water-soluble host:guest complexes with lipophilic molecules that hide in the their cavity. The aim of the review is to describe the historical background, the structure and proprieties of natural cyclodextrins and their derivatives, their physico-chemical properties and toxicological profile. We also describe the different methods to prepare the inclusion complexes and give an overview of the various applications of such complexes in the different fields. The review discusses and summarizes the most recent literature of cyclodextrins and their application in order to give a comprehensive treatment of the main features of these tools widely used to improve the solubility and bioavailability of many compounds used in the biotechnological and pharmaceutical fields.

The present study describes the selective halogenation at the β- or meso-position of the porphyrin macrocycle. The reactions of deuteroporphyrin IX dimethyl ester, mesoporphyrin III dimethyl ester and their Cu(II) and Ni(II) complexes with N-bromosuccinimide or phenylselenyl chloride were investigated. It could be observed that when the bromination of deuteroporphyn IX dimethyl ester using NBS took place, the isolated products were the result of an electrophilic substitution in β-free porphyrin ring positions. Employing the same reagent for halogenating mesoporphyrin III dimethyl ester, which does not possess β-free position, different derivatives were obtained from the allylic bromination of the ethyl side chain. When phenylselenyl chloride was used as halogenating agent with deuteroporphyn IX dimethyl ester or its Cu(II) complex, in both cases the replacement of β-free hydrogen atoms by phenylselenyl group was afforded. When the Ni(II) mesoporphyrin III dimethyl ester was used the desired and selective replacement of meso hydrogen atoms of aromatic ring by chlorine atoms was obtained. The structural assignment of the porphyrin derivatives thus obtained was performed by high-resolution mass spectrometry and detailed analysis of the NMR spectra.

Background: 1,2,4-Triazine is a prominent structural core system present in numerous natural and synthetic biologically active compounds. The existing synthetic methodologies have mostly focused on 3,6- disubstituted-1,2,4-triazines and 3,5,6-trisubstituted-1,2,4-triazines. However, until now only a few methods have been developed for making 3,5-disubstituted-1,2,4-triazines. Objective: The primary objective of the study was to find an efficient and simple way to construct 3,5- disubstituted-1,2,4-triazines. Method: The arylethene (0.24 mmol), I2 (0.22 mmol), IBX(0.24mmol.) and DMSO (2 mL) were added to a round-bottomed flask equipped with a magnetic stirring bar. The reaction mixture was agitated at 110°C under air for 3h, then amidrazone (0.2 mmol) was added to the mixture and the reaction continued at 110°C for another 1.5h. Afterwards, water (20mL) was added and the reaction mixture was extracted with ethyl acetate (3 × 50mL). The organic phases was combined and concentrated under reduced pressure to distill ethyl acetate. The residue was further purified by column chromatography on a silica gel column with petroleum / ethyl acetate (5:1) as eluent to obtain the desired products. Results: We developed an operationally simple way of regioselectively synthesizing 3,5-disubstituted-1,2,4- triazines by a coupled domino strategy with terminal aryl alkenes and amidrazones in one-pot. The overall process involves three different reactions: iodination, Kornblum oxidation and condensation. Conclusion: The strategies exhibit high performance with moderate to high yields, using simple and readily available terminal aryl alkenes and amidrazones, representing a powerful tool for the formation of potentially biologically active derivatives.