Chitosan has garnered much interest due to its properties and possible applications. Every year the number of publications and patents based on this polymer increase. Chitosan exhibits poor ...solubility in neutral and basic media, limiting its use in such conditions. Another serious obstacle is directly related to its natural origin. Chitosan is not a single polymer with a defined structure but a family of molecules with differences in their composition, size, and monomer distribution. These properties have a fundamental effect on the biological and technological performance of the polymer. Moreover, some of the biological properties claimed are discrete. In this review, we discuss how chitosan chemistry can solve the problems related to its poor solubility and can boost the polymer properties. We focus on some of the main biological properties of chitosan and the relationship with the physicochemical properties of the polymer. Then, we review two polymer applications related to green processes: the use of chitosan in the green synthesis of metallic nanoparticles and its use as support for biocatalysts. Finally, we briefly describe how making use of the technological properties of chitosan makes it possible to develop a variety of systems for drug delivery.
The broad interdisciplinary nature of biocatalysis fosters innovation, as different technical fields are interconnected and synergized. A way to depict that innovation is by conducting a survey on ...patent activities. This paper analyses the intellectual property activities of the last five years (2014–2019) with a specific focus on biocatalysis applied to asymmetric synthesis. Furthermore, to reflect the inventive and innovative steps, only patents that were granted during that period are considered. Patent searches using several keywords (e.g., enzyme names) have been conducted by using several patent engine servers (e.g., Espacenet, SciFinder, Google Patents), with focus on granted patents during the period 2014–2019. Around 200 granted patents have been identified, covering all enzyme types. The inventive pattern focuses on the protection of novel protein sequences, as well as on new substrates. In some other cases, combined processes, multi-step enzymatic reactions, as well as process conditions are the innovative basis. Both industries and academic groups are active in patenting. As a conclusion of this survey, we can assert that biocatalysis is increasingly recognized as a useful tool for asymmetric synthesis and being considered as an innovative option to build IP and protect synthetic routes.
The increasing relevance of cascade reactions in biocatalysis has sparked a great interest for enzyme co-immobilization. Enzyme co-immobilization allows access to some kinetic advantages that in some ...instances are necessary to get the desired product, avoiding side-reactions. However, the kinetic effect is very relevant mainly at the initial reaction rates, while it may be less relevant in the whole reaction course, depending on the kinetic parameters of the involved enzymes. This review not only critically discusses the advantages but also the drawbacks of enzymes co-immobilization: immobilization on the same support and surface, under similar conditions, discarding the whole biocatalyst when one of the co-immobilized enzymes is inactivated. We will discuss when co-immobilization is almost compulsory, when the advantages of co-immobilization may not be enough to compensate their problems and when it should be fully discarded. The co-immobilization of cofactors and enzymes bears special interest, as this can open up the opportunity to the building of artificial cells and extremely complex one-pot transformations. Finally, some recent strategies to overcome some the co-immobilization problems will be presented.
•Enzyme co-immobilization raises many problems in biocatalysts design.•Enzyme co-immobilization has some kinetic advantages regarding initial rates.•Enzyme co-immobilization is, in certain cases, necessary.•Co-immobilization of enzymes and cofactors opens up the possibility of building “synthetic cells”.•Some strategies have been developed to solve the problems of enzymes co-immobilization.
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•Magnetic biocatalysts allow their easy recovery and simplifies operational processing.•Magnetic stirring enhances biocatalyst life-time and reduce diffusion limitations.•Medium-size ...magnetic biocatalysts avoid problems if compared to nano-size ones.•Magnetic biocatalysts can be successfully applied in many industrial areas.
The use of magnetic biocatalysts is highly beneficial in bioprocesses technology, as it allows their easy recovering and enhances biocatalyst lifetime. Thus, it simplifies operational processing and increases efficiency, leading to more cost-effective processes. The use of small-size matrices as carriers for enzyme immobilization enables to maximize surface area and catalysts loading, also reducing diffusion limitations. As highly expensive nanoparticles (nm size) usually aggregate, their application at large scale is not recommended. In contrast, the use of magnetic micro-macro (µm-mm size) matrices leads to more homogeneous biocatalysts with null or very low aggregation, which facilitates an easy handling and recovery. The present review aims to highlight recent trends in the application of medium-to-high size magnetic biocatalysts in different areas (biodiesel production, food and pharma industries, protein purification or removal of environmental contaminants). The advantages and disadvantages of these above-mentioned magnetic biocatalysts in bioprocess technology will be also discussed.
Apart from being one of the most important intermediates in chemical synthesis, broadly used in the formation of C–C bonds among other processes, the β-dicarbonyl structure is present in a huge ...number of biologically and pharmaceutically active compounds. In fact, mainly derived from the well-known antioxidant capability associated with the corresponding enol tautomer, β-diketones are valuable compounds in the treatment of many pathological disorders, such as cardiovascular and liver diseases, hypertension, obesity, diabetes, neurological disorders, inflammation, skin diseases, fibrosis, or arthritis; therefore, the synthesis of these structures is an area of overwhelming interest for organic chemists. This paper is devoted to the advances achieved in the last ten years for the preparation of 1,3-diketones, using different chemical (Claisen, hydration of alkynones, decarboxylative coupling) or catalytic (biocatalysis, organocatalytic, metal-based catalysis) methodologies: Additionally, the preparation of branched β-dicarbonyl compounds by means of α-functionalization of non-substituted 1,3-diketones are also discussed.
The role and power of biocatalysis in sustainable chemistry has been continuously brought forward step by step to its present outstanding position. The problem‐solving capabilities of biocatalysis ...have been realized by numerous substantial achievements in biology, chemistry and engineering. Advances and breakthroughs in the life sciences and interdisciplinary cooperation with chemistry have clearly accelerated the implementation of biocatalytic synthesis in modern chemistry. Resource‐efficient biocatalytic manufacturing processes have already provided numerous benefits to sustainable chemistry as well as customer‐centric value creation in the pharmaceutical, food, flavor, fragrance, vitamin, agrochemical, polymer, specialty, and fine chemical industries. Biocatalysis can make significant contributions not only to manufacturing processes, but also to the design of completely new value‐creation chains. Biocatalysis can now be considered as a key enabling technology to implement sustainable chemistry.
The golden age of biocatalysis: Biocatalysis can shorten chemical process routes and improve sustainability, as well as using cheaper and bio‐based raw materials, thereby reducing greenhouse gas emissions. Biocatalysis is well positioned to tackle synthetic challenges throughout process design and improve safety, health, economic and environmental aspects of large‐scale industrial production (difficulty levels: L=light; M=medium; D=difficult).
The development of efficient syntheses for enantiomerically enriched α-hydroxy ketones is an important research focus in the pharmaceutical industry. For example, α-hydroxy ketones are found in ...antidepressants, in selective inhibitors of amyloid-β protein production (used in the treatment of Alzheimer’s), in farnesyl transferase inhibitors (Kurasoin A and B), and in antitumor antibiotics (Olivomycin A and Chromomycin A3). Moreover, α-hydroxy ketones are of particular value as fine chemicals because of their utility as building blocks for the production of larger molecules. They can also be used in preparing many other important structures, such as amino alcohols, diols, and so forth. Several purely chemical synthetic approaches have been proposed to afford these compounds, together with some organocatalytic strategies (thiazolium-based carboligations, proline α-hydroxylations, and so forth). However, many of these chemical approaches are not straightforward, lack selectivity, or are economically unattractive because of the large number of chemical steps required (usually combined with low enantioselectivities). In this Account, we describe three different biocatalytic approaches that have been developed to efficiently produce α-hydroxy ketones: (i) The use of thiamine diphosphate-dependent lyases (ThDP-lyases) to catalyze the umpolung carboligation of aldehydes. Enantiopure α-hydroxy ketones are formed from inexpensive aldehydes with this method. Some lyases with a broad substrate spectrum have been successfully characterized. Furthermore, the use of biphasic media with recombinant whole cells overexpressing lyases leads to productivities of ∼80−100 g/L with high enantiomeric excesses (up to >99%). (ii) The use of hydrolases to produce α-hydroxy ketones by means of (in situ) dynamic kinetic resolutions (DKRs). Lipases are able to successfully resolve racemates, and many outstanding examples have been reported. However, this approach leads to a maximum theoretical yield of 50%. As a means of overcoming this problem, these traditional lipase-catalyzed kinetic resolutions are combined with racemization of remnant substrate, which can be done in situ or in separate compartments. Examples showing high conversions (>90%) and enantiomeric excesses (>99%) are described. (iii) Whole-cell redox processes, catalyzed by several microorganisms, either by means of free enzymes (applying a cofactor regeneration system) or by whole cells. Through the use of redox machineries, different strategies can lead to high yields and enantiomeric excesses. Some enantiopure α-hydroxy ketones can be formed by reductions of diketones and by selective oxidations of vicinal diols. Likewise, some redox processes involving sugar chemistry (involving α-hydroxy ketones) have been developed on the industrial scale. Finally, the redox whole-cell concept allows racemizations (and deracemizations) as well. These three strategies provide a useful and environmentally friendly synthetic toolbox. Likewise, the field represents an illustrative example of how biocatalysis can assist practical synthetic processes, and how problems derived from the integration of natural tools in synthetic pathways can be efficiently tackled to afford high yields and enantioselectivities.
The necessity of more sustainable conditions that follow the twelve principles of Green Chemistry have pushed researchers to the development of novel reagents, catalysts and solvents for greener ...asymmetric methodologies. Solvents are in general a fundamental part for developing organic processes, as well as for the separation and purification of the reaction products. By this reason, in the last years, the application of the so-called green solvents has emerged as a useful alternative to the classical organic solvents. These solvents must present some properties, such as a low vapor pressure and toxicity, high boiling point and biodegradability, and must be obtained from renewable sources. In the present revision, the recent application of these biobased solvents in the synthesis of optically active compounds employing different catalytic methodologies, including biocatalysis, organocatalysis and metal catalysis, will be analyzed to provide a novel tool for carrying out more ecofriendly organic processes.
Applied Biotransformations in Green Solvents Hernáiz, María J.; Alcántara, Andrés R.; García, José I. ...
Chemistry : a European journal,
August 16, 2010, Letnik:
16, Številka:
31
Journal Article
Recenzirano
The definite interest in implementing sustainable industrial technologies has impelled the use of biocatalysts (enzymes or cells), leading to high chemo‐, regio‐ and stereoselectivities under mild ...conditions. As usual substrates are not soluble in water, the employ of organic solvents is mandatory. We will focus on different attempts to combine the valuable properties of green solvents with the advantages of using biocatalysts for developing cleaner synthetic processes.
The future is bio, the future is green: Interest in implementing sustainable industrial technologies has propelled the use of biocatalysts (enzymes or cells), leading to high chemo‐, regio‐ and stereoselectivity under mild conditions. We focus on different attempts to combine the valuable properties of green solvents with the advantages of using biocatalysts for developing cleaner synthetic processes (see figure).
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