3.2.3. Hydroformylation 2467 3.2.4. Dimerization 2468 3.2.5. Oxidative Cleavage and Ozonolysis 2469 3.2.6. Metathesis 2470 4. Terpenes 2472 4.1. Pinene 2472 4.1.1. Isomerization: R-Pinene 2472 4.1.2. Epoxidation of R-Pinene 2475 4.1.3. Isomerization of R-Pinene Oxide 2477 4.1.4. Hydration of R-Pinene: R-Terpineol 2478 4.1.5. Dehydroisomerization 2479 4.2. Limonene 2480 4.2.1. Isomerization 2480 4.2.2. Epoxidation: Limonene Oxide 2480 4.2.3. Isomerization of Limonene Oxide 2481 4.2.4. Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481

Chemical Routes for the Transformation of Biomass into Chemicals

Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820020503%2941%3A9%3C1460%3A%3AAID-ANIE11111460%3E3.0.CO%3B2-N

Dynamic covalent chemistry.

Roger Sheldon (1942) received a PhD in organic chemistry from the University of Leicester (UK) in 1967. This was followed by post-doctoral studies with Prof. Jay Kochi in the U.S. From 1969 to 1980 he was with Shell Research in Amsterdam and from 1980 to 1990 he was R&D Director of DSM Andeno. In 1991 he moved to his present position as Professor of organic chemistry and catalysis at the Delft University of Technology (The Netherlands). His primary research interests are in the application of catalytic methodologies—homogeneous, heterogeneous and enzymatic—in organic synthesis, particularly in relation to fine chemicals production. He developed the concepts of E factors and atom utilization for assessing the environmental impact of chemical processes.

Biocatalysis in ionic liquids

Enzyme biocatalysis plays a very relevant role in the development of many chemical industries, e.g., energy, food or fine chemistry. To achieve this goal, enzyme immobilization is a usual pre-requisite as a solution to get reusable biocatalysts and thus decrease the price of this relatively expensive compound. However, a proper immobilization technique may permit far more than to get a reusable enzyme; it may be used to improve enzyme performance by improving some enzyme limitations: enzyme purity, stability (including the possibility of enzyme reactivation), activity, specificity, selectivity, or inhibitions. Among the diverse immobilization techniques, the use of pre-existing supports to immobilize enzymes (via covalent or physical coupling) and the immobilization without supports [enzyme crosslinked aggregates (CLEAs) or crystals (CLECs)] are the most used or promising ones. This paper intends to give the advantages and disadvantages of the different existing immobilization strategies to solve the different aforementioned enzyme limitations. Moreover, the use of nanoparticles as immobilization supports is achieving an increasing importance, as the nanoparticles versatility increases and becomes more accessible to the researchers. We will also discuss here some of the advantages and drawbacks of these non porous supports compared to conventional porous supports. Although there are no universal optimal solutions for all cases, we will try to give some advice to select the optimal strategy for each particular enzyme and process, considering the enzyme properties, nature of the process and of the substrate. In some occasions the selection will be compulsory, for example due to the nature of the substrate. In other cases the optimal biocatalyst may depend on the company requirements (e.g., volumetric activity, enzyme stability, etc).

Potential of Different Enzyme Immobilization Strategies to Improve Enzyme Performance

Enzymes are versatile catalysts in the laboratory and on an industrial scale. To broaden their applicability in the laboratory and to ensure their (re)use in manufacturing the stability of enzymes can often require improvement. Immobilisation can address the issue of enzymatic instability. Immobilisation can also help to enable the employment of enzymes in different solvents, at extremes of pH and temperature and exceptionally high substrate concentrations. At the same time substrate-specificity, enantioselectivity and reactivity can be modified. However, most often the molecular and physical–chemical bases of these phenomena have not been elucidated yet. This tutorial review focuses on the understanding of enzyme immobilisation.

Understanding enzyme immobilisation

Peptide bond synthesis was performed on PEGA beads under microwave radiations. Classical chemical coupling as well as thermolysin catalyzed synthesis was studied, and the effect of microwave radiations on reaction kinetics, beads' integrity, and enzyme activity was assessed. Results demonstrate that microwave radiations can be profitably exploited to improve reaction kinetics in solid phase peptide synthesis when both chemical and biocatalytic strategies are used.

/pdf/effect-of-microwave-radiation-on-enzymatic-and-chemical-4s1mh7c9ti.pdf

Effect of Microwave Radiation on Enzymatic and Chemical Peptide Bond Synthesis on Solid Phase

Covalently immobilised penicillin G acylase (PGA-450) accepts in toluene, at controlled water activity (aw), a broad range of amino compounds as nucleophiles in kinetically controlled acylation. Hydrolytic reactions were prevented and complete conversions were achieved in short times even when working with an equimolar concentration of the substrates. The recovery of the products was facile, leading to high isolation yields. The obtained N-acylated derivatives of L-amino acids can be used in further reactions, since no purification steps are required in such conditions. This opens new perspectives to the application of PGA in selective protection of the amino function for peptide synthesis. All attempts to perform esterification and transesterification reactions with PGA in toluene, at the same aw as used for the acylation of amino compounds, were unsuccesful.

/pdf/quantitative-acylation-of-amino-compounds-catalysed-by-3bkqvdek8y.pdf

Quantitative acylation of amino compounds catalysed by penicillin G acylase in organic solvent at controlled water activity

Peroxygenase-Driven Ethylbenzene Hydroxylation in a Rotating Bed Reactor

A novel catalytic property of penicillin G amidase (PGA) is described. Unexpectedly, the enzyme can hydrolyse hydrazide bonds with good efficiency, and in solution the enzyme shows a selectivity that is similar to phenylacetamides. The hydrolysis of phenylacetic hydrazides releases hydrazine, but no inhibition due to the formation of such reactive compounds was observed. This novel catalytic property was assayed also on a solid phase as a pioneering route for the design of enzyme-cleavable linkers and masked scavengers for ketones. On a solid phase a phenylacetic hydrazide conipound was chemically synthesised on PEGA 1 9 0 0 and PEGA + (two co-polymers of acrylamide and ethylene glycol) and the efficiency of PGA in the release of phenylacetic acid depended on the diffusion of the protein inside the polymer. On PEGA + the enzyme, as previously described, shows a good diffusion due to an improved electrostatic interaction with PGA thus achieving good hydrolytic conversions.

Penicillin G Amidase-Catalysed Hydrolysis of Phenylacetic Hydrazides on a Solid Phase: A New Route to Enzyme-Cleavable Linkers

Solid-phase synthesis is the method of choice for peptide preparation in both research and industrial settings. The whole synthetic process is governed by the initial functionalization of the resin...

/pdf/calculating-resin-functionalization-in-solid-phase-peptide-41de32nzca.pdf

Alessandra Basso

Papers

Effect of Microwave Radiation on Enzymatic and Chemical Peptide Bond Synthesis on Solid Phase

Quantitative acylation of amino compounds catalysed by penicillin G acylase in organic solvent at controlled water activity

Peroxygenase-Driven Ethylbenzene Hydroxylation in a Rotating Bed Reactor

Penicillin G Amidase-Catalysed Hydrolysis of Phenylacetic Hydrazides on a Solid Phase: A New Route to Enzyme-Cleavable Linkers

Calculating Resin Functionalization in Solid-Phase Peptide Synthesis Using a Standardized Method based on Fmoc Determination.