Weckhuysen and Jihong Yu. The article was first published on 24 Sep Chem. The article was first published on 21 Dec Chem. The article was first published on 16 Nov Chem.
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The article was first published on 05 Oct Chem. Review Article Fluid catalytic cracking: recent developments on the grand old lady of zeolite catalysis E. Vogt and B. The article was first published on 18 Sep Chem. Review Article The formation and degradation of active species during methanol conversion over protonated zeotype catalysts U. Olsbye, S.
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Wang and W. The article was first published on 17 Jul Chem. Rangnekar, N. Mittal, B. Elyassi, J. Caro and M. The article was first published on 09 Jul Chem. Review Article Phosphorus promotion and poisoning in zeolite-based materials: synthesis, characterisation and catalysis Hendrik E. The article was first published on 05 Jun Chem. Parmentier, Krijn P.
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The article was first published on 26 May Chem. The article was first published on 18 May Chem. There are very few examples of enzymatic aryl couplings and, thus, this will only be used when alternative chemical methods are not applicable. Another criterion used to decide what type of catalyst is used is that the process must include isolation of the product in acceptable yield and purity. Although significant advances have been made for the use of enzymes in the presence of organic solvents and with substrates that are poorly soluble in aqueous media, problems can still exist.
Conversely, if the product is very water soluble, isolation of the desired material can present a significant challenge. Chemical transformations usually have the advantage of a number of solvent systems being available to perform the transformation and subsequent isolation.
The scale-up of chemical catalytic reactions is usually an exercise in normal process chemistry. Synthesis of the ligands and transition metal catalyst usually present few problems, as the amounts are much lower than for the reaction itself. However, to improve specificity and efficiency new catalysts have to be prepared and tried. This can be a time-consuming exercise. On the biocatalytic side, modifications to the original enzyme can be made by genetic modifications and rapid screening. This allows selectivity, stability and other issues to be addressed.
On the other hand, these studies can be time-consuming and may require more resources than just making a new ligand. The criteria of cost and speed also contribute to the choice of catalyst system. In the early stages of development of a drug candidate, speed is of the essence but cost is still important.
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Precedence and the availability of the catalyst will be key factors. For larger scale work, the pendulum may swing from a chemical method to a biocatalytic one.
A Computational Chemistry Approach for the Catalytic Cycle of AHAS
For commercial production, biological routes are often cost effective. However, it must be remembered that the catalytic step is usually part of a synthetic sequence. The substrate for the catalytic step has to be prepared and the product converted to the final target molecule.
As an example, consider the synthesis of S -2,3-dihydro-1 H -indolecarboxylic acid. It was necessary to replace an inefficient route that used a late stage resolution. Many alternatives were considered but the most efficient used a copper-catalysed cyclisation to form the product.
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To prepare the substrate for this reaction, three enzymatic approaches were identified Figure 1. When the alternative methods were compared in terms of costs and efficiencies including the number of steps , the ammonia lyase approach was the route of choice as the starting material is readily available 7 , 8.
Although there are a number of approaches to ortho -halocinnamic acid 8 , the Heck reaction provides an efficient synthesis. Without the use of this palladium-catalysed reaction, the remainder of the sequence would not be efficient. Thus, the overall sequence shows that biocatalysts and chemical catalysts are required to effect an efficient, sustainable process.
Some routes to S -2,3-dihydro-1H-indolecarboxylic acid. In summary the choice between a chemical and a biological catalyst depends on many factors.
Related Catalysis: A Review of Chemical Literature
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