Polyester is widely used in biomedical, textile, and food packaging fields. Therefore, enhancing it with antimicrobial properties would be a significant advancement. In this paper, a series of ...borneol-triazine polyesters (BTPs) with different structures are synthesized through room temperature polycondensation. The structure and composition of BTPs are systematically characterized by 1H NMR, FTIR and GPC. Antimicrobial results reveal that the ability of BTPs to resist bacterial or fungal adhesion is directly related to the polymer structure. When the polymer chain of BTPs adopts a rigid structure, they exhibit excellent anti-adhesive and inhibitory performances against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Meanwhile, the as-synthesized BTPs poses a fungal-repelling effect on common fungal strains (Aspergillus niger) for up to 30 d. Further studies have shown that a stereochemical structure brought by borneol is key for imparting effective antimicrobial properties to BTPs. In addition, BTPs are non-leaching materials with low cellular cytotoxicity. Taking into consideration, BTP provides a potential strategy for preparing a new class of antimicrobial polyester materials.
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•BTPs, as a series of new type of antimicrobial polyesters, are synthesized.•BTPs can inhibit the spread of microorganisms, including bacteria and fungi.•BTPs achieves antimicrobial adhesion by stereochemistry strategy.•The rigidity of BTPs have a significant impact on antimicrobial adhesion.•BTPs are non-leaching antimicrobial polymers.
The development of new methods for the direct functionalization of unactivated C–H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic ...enantioselective functionalization of C–H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation. Our analysis serves to document the considerable and rapid progress within in the field, while also highlighting limitations of current methods.
The Cover Feature summarizes the results of a joint computational and experimental study demonstrating that faster racemization through water‐catalyzed enolization could result in faster ...deracemization of a scalemic slurry of a chiral hydrazine derivative. More information can be found in the Article by Michael Mauksch, Svetlana B. Tsogoeva and co‐workers.
A highly enantioselective synthesis of 5,13‐disubstituted dibenzod,d′benzo1,2‐b:4,3‐b′dithiophenes is reported. Key for the successful assembly of these helical architectures is the last two ...successive Au‐catalyzed intramolecular alkyne hydroarylation events. Specifically, the second cyclization is the enantiodetermining step of the whole process and provides the desired helicenes with excellent ee values when a TADDOL‐derived 1,2,3‐(triazolium)phosphonite moiety (TADDOL: α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol) is employed as an ancillary ligand. The absolute stereochemistry of the newly prepared structures has been determined by X‐ray crystallography to be P; the optical properties of these heterohelicenes are also reported. A three‐step procedure was subsequently developed that allows the transformation of the initially obtained dithia5helicenes into dithia9helicenes without erosion of the enantiopurity.
Among many problems of a fundamental value in the heteroatom chemistry the mechanism and stereochemistry of the nucleophilic substitution reaction at the phosphorus and other heteroatom centres have ...attracted great attention of phosphorus chemists already in the middle of the last century. This review, which does not have a comprehensive character, summarizes the selected original contributions aimed at solution of the mechanism of SN2−P reaction and its relationship with stereochemistry. The breakthrough in these studies was the Westheimer's concept and his rules which is presented at the beginning of this article. Next, a series of papers is presented where the stereochemistry of the substitution at phosphorus was investigated in cyclic five‐, four‐ and six‐membered ring phosphorus compound. The majority of these reactions have been found to occur with retention of the P‐configuration. In the third part of this account, the selected examples of substitution reactions at phosphorus in acyclic compounds are discussed. As the results of all the investigations discussed did not allow to undoubtedly ascribe the mechanism (SN2 or A−E) to the investigated reactions, in the last part the SN‐P reactions are presented, the mechanism of which has been established by combination of the stereochemical and DFT‐studies.
This review summarizes the selected results of the old and recent studies on the nucleophilic substitution reactions at the tetracoordinate phosphorus atom (SN−P(IV)). The stereochemistry inversion, retention and mechanisms concerted SN2−P, stepwise (A−E)−P of these reactions as well as their relationship are presented.
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•Immobilised enzymes, the pros and cons of their use in large industrial processes are reviewed.•Parameters for economically viable biocatalytic processes: recyclability, enzyme ...selectivity and reaction turnover are discussed.•Large-scale applications of immobilized enzymes in the food, chemical, pharmaceutical, cosmetic and medical device industries are reported.•The use of immobilized enzymes in the industrial manufacture of foodstuffs, chiral API’s and specialty chemicals is described.•The use of immobilized urease and lipase in medical devices is described, enzymatic biosensors being also included.
The use of immobilized enzymes is now a routine process for the manufacture of many industrial products in the pharmaceutical, chemical and food industry. Some enzymes, such as lipases, are naturally robust and efficient, can be used for the production of many different molecules and have a wide range of industrial applications thanks to their broad selectivity. As an example, lipase from Candida antarctica (CalB) has been used by BASF to produce chiral compounds, such as the herbicide Dimethenamide-P, which was previously made chemically. The use of the immobilized enzyme has provided significant advantages over a chemical process, such as the possibility to use equimolar concentration of substrates, obtain an enantiomeric excess > 99%, use relatively low temperatures (< 60 °C) in organic solvent, obtain a single enantiomer instead of the racemate as in the chemical process and use a column configuration that allows dramatic increases in productivity. This process would not have been possible without the use of an immobilized enzyme, since it runs in organic solvent 1.
Some more specific enzymes, like transaminases, have required protein engineering to become suitable for applications in production of APIs (Active Pharmaceutical Ingredients) in conditions which are extreme for a wild type enzyme. The process developed by Merck for sitagliptin manufacture is a good example of challenging enzyme engineering applied to API manufacture. The previous process of sitagliptin involved hydrogenation of enamine at high pressure using a rhodium-based chiral catalyst. By developing an engineered transaminase, the enzymatic process was able to convert 200 g/l of prositagliptin in the final product, with e.e. >99.5% and using an immobilized enzyme in the presence of DMSO as a cosolvent 2.
For all enzymes, the possibility to be immobilized and used in a heterogeneous form brings important industrial and environmental advantages, such as simplified downstream processing or continuous process operations. Here, we present a series of large-scale applications of immobilized enzymes with benefits for the food, chemical, pharmaceutical, cosmetics and medical device industries, some of which have been scarcely reported on previously.
In general, all enzymatic reactions can benefit from the immobilization, however, the final choice to use them in immobilized form depends on the economic evaluation of costs associated with their use versus benefits obtained in the process. It can be concluded that the benefits are rather significant, since the use of immobilized enzymes in industry is increasing.
Conspectus As Pasteur noted more than 150 years ago, asymmetry exists in matter at all organization levels. Biopolymers such as proteins or DNA adopt one-handed conformations, as a result of the ...chirality of their constituent building blocks. Even at the level of elementary particles, asymmetry exists due to parity violation in the weak nuclear force. While the origin of homochirality in living systems remains obscure, as does the possibility of its connection with broken symmetries at larger or smaller length scales, its centrality to biomolecular structure is clear: the single-handed forms of bio(macro)molecules interlock in ways that depend upon their handednesses. Dynamic artificial systems, such as helical polymers and other supramolecular structures, have provided a means to study the mechanisms of transmission and amplification of stereochemical information, which are key processes to understand in the context of the origins and functions of biological homochirality. Control over stereochemical information transfer in self-assembled systems will also be crucial for the development of new applications in chiral recognition and separation, asymmetric catalysis, and molecular devices. In this Account, we explore different aspects of stereochemistry encountered during the use of subcomponent self-assembly, whereby complex structures are prepared through the simultaneous formation of dynamic coordinative (N → metal) and covalent (NC) bonds. This technique provides a useful method to study stereochemical information transfer processes within metal–organic assemblies, which may contain different combinations of fixed (carbon) and labile (metal) stereocenters. We start by discussing how simple subcomponents with fixed stereogenic centers can be incorporated in the organic ligands of mononuclear coordination complexes and communicate stereochemical information to the metal center, resulting in diastereomeric enrichment. Enantiopure subcomponents were then incorporated in self-assembly reactions to control the stereochemistry of increasingly complex architectures. This strategy has also allowed exploration of the degree to which stereochemical information is propagated through tetrahedral frameworks cooperatively, leading to the observation of stereochemical coupling across more than 2 nm between metal stereocenters and the enantioselective synthesis of a face-capped tetrahedron containing no carbon stereocenters via a stereochemical memory effect. Several studies on the communication of stereochemistry between the configurationally flexible metal centers in tetrahedral metal–organic cages have shed light on the factors governing this process, allowing the synthesis of an asymmetric cage, obtained in racemic form, in which all symmetry elements have been broken. Finally, we discuss how stereochemical diversity leads to structural complexity in the structures prepared through subcomponent self-assembly. Initial use of octahedral metal templates with facial stereochemistry in subcomponent self-assembly, which predictably gave rise to structures of tetrahedral symmetry, was extended to meridional metal centers. These lower-symmetry linkages have allowed the assembly of a series of increasingly intricate 3D architectures of varying functionality. The knowledge gained from investigating different aspects of the stereochemistry of metal-templated assemblies thus not only leads to new means of structural control but also opens pathways toward functions such as stereoselective guest binding and transformation.
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