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Asymmetric Reduction of C=N Bonds by Imine Reductases and Reductive Aminases
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Matthias Höhne, Philipp Matzel, Martin Gand
Several enzymes exist which reduce a C=N bond during the reaction (Fig. 14.2). The focus of this chapter is on imine reductases suitable for apolar secondary amine synthesis (Fig 14.2A). Enzymes converting substrates that bear a carboxylic acid functional group will also be summarized (Fig. 14.2B). C=N-double bonds also occur in intermediates during the deamination of primary amines and amino acids: The enzymes amine dehydrogenases and amino acid dehydrogenases, which catalyze these deaminations (Fig. 14.2B), differ from IREDs as they are limited to the conversion/formation of primary amines, and thus are not discussed in this chapter. Differentiation of IREDs from other similar enzymes, which process an imine intermediate during their catalytic cycle.
Oils
Published in Heather A.E. Benson, Michael S. Roberts, Vânia Rodrigues Leite-Silva, Kenneth A. Walters, Cosmetic Formulation, 2019
Fabricio Almeida de Sousa, Vânia Rodrigues Leite-Silva
Carboxylic acids can be esterified by alcohols in the presence of a suitable acidic catalyst as illustrated in Scheme 10.1 . The initial step is protonation of the acid to give an oxonium ion (1) that can then undergo an exchange reaction with an alcohol to give the intermediate (2), and that can lose a proton to become an ester (3). Each step in the process is reversible, but in the presence of a large excess of alcohol, the equilibrium point of the reaction is displaced so that esterification proceeds virtually to completion. However, in the presence of water, which is a stronger electron donor than are aliphatic alcohols, formation of the intermediate (2) is not favoured and esterification will not proceed fully.
Formaldehyde
Published in William J. Rea, Kalpana D. Patel, Reversibility of Chronic Disease and Hypersensitivity, Volume 4, 2017
William J. Rea, Kalpana D. Patel
Acetic acid is one of the simplest carboxylic acids. It is an important chemical reagent and industrial chemical, mainly used in the production of cellulose acetate, especially for photographic film and polyvinyl acetate for wood glue, as well as synthetic fibers and fabrics. In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is used under the food additive code E260 as an acidity regulator and as a condiment. As a food additive, it is approved for usage in the EU,3 the United States,4 Australia, and New Zealand.5
Standardizing and increasing the utility of lipidomics: a look to the next decade
Published in Expert Review of Proteomics, 2020
Yuqin Wang, Eylan Yutuc, William J Griffiths
Simple fatty acids have been analyzed by GC-MS for decades [87] and were one of the first lipid classes to be analyzed by FAB-MS in the 1970’s [19,88]. For analysis by GC-MS the carboxylic acid group is usually converted to an ester. Many different types of fatty acyl esters have been generated for GC-MS analysis each with their own merits [23,85,89,90]. Besides the popular derivatization to methyl esters (fatty acyl methyl esters, FAME), two other derivatizations with particular merit are to picolinyl esters [23] and to pentafluorbenzyl esters [85]. Picolinyl esters fragment in the EI source through a charge-mediated mechanism to give a series of fragment-ions resulting from cleavage of successive carbon-carbon bonds, this allows the determination of the position of double bonds, cyclic groups and with trimethylsilylether derivatization of alcohol groups, the site of hydroxylations [23]. The advantage of derivatization to pentafluorobenzyl esters is that with negative chemical ionization dissociative electron capture occurs to give [RCO2]− ions allowing detection of chromatographically separated fatty acid derivatives at high sensitivity [85].
Transfer of metals in the liquids of electronic cigarettes
Published in Inhalation Toxicology, 2020
Efthimios Zervas, Niki Matsouki, Grigorios Kyriakopoulos, Stavros Poulopoulos, Theophilos Ioannides, Paraskevi Katsaounou
Two main mechanisms have been proposed for this reaction, the free radical and the ionic (Młochowski et al. 2003). Aldehyde oxidation reaction can be carried out in acidic, basic or neutral solutions using a number of oxidizing agents (Shaikh and Hong 2013), but aldehydes can also be oxidized to carboxylic acids by atmospheric oxygen (Liu et al. 2018). Liquid phase oxidations are known as autoxidations, since they are often subject to autocatalysis by the products (Hendriks et al. 1978). These types of reactions are used to convert aldehydes to carboxylic acids and can be performed even without metal catalysts. However, since the rate-determining initiation step involves the reaction of the metal oxidant with the aldehyde substrate, metals such as Mn(II), Co(II), Fe(II), Ni(II), Ru(II) and Cu(II) act as catalysts (Esfandiari et al. 2013; Brewster et al. 2016; Jiang et al. 2018). Consequently, the presence of a wire can increase the formation of organic acids. During ketone oxidation, the first intermediate product is α-ketohydroperoxid (Patnaik et al. 1987). Decay and reaction of this hydroperoxide forms a wide range of products including acids. Both oxidation reactions can be performed by dioxygen (Bregeault et al. 2001; Wang et al. 2016). It is, therefore, expected that the presence of air facilitates this oxidation. Ketones also easily undergo metal-catalyzed autoxidation to produce carboxylic acids resulting from C–C bond cleavage (Bregeault et al., 2001). The organic acids formed can easily react with metals, thus, the concentration of the metals in the e-liquids increases (Sleiman et al. 2016).
Refining the structure−activity relationships of 2-phenylcyclopropane carboxylic acids as inhibitors of O-acetylserine sulfhydrylase isoforms
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Joana Magalhães, Nina Franko, Giannamaria Annunziato, Marco Pieroni, Roberto Benoni, Anna Nikitjuka, Andrea Mozzarelli, Stefano Bettati, Anna Karawajczyk, Aigars Jirgensons, Barbara Campanini, Gabriele Costantino
To investigate whether the carboxylic acid functionality might be modified, we replaced it with isosteric groups. Among the set of possible substituents, sulphonamides, a tetrazole ring and amides were initially investigated. While the sulphonamide group is a nonplanar isoster of the carboxylic acid, the tetrazole is planar and presents a similar acidity. On a similar vein, substituted amides were prepared because it is well known that the nature of the substituents might affect the selectivity of action toward different bacterial strains, either Gram-positive or Gram-negative29,30. For instance, in the case of sulphonamide drugs, potency and selectivity are modulated by the substituent at the amidic nitrogen31. Finally, we investigated the benzyl group attached at the C1 of the cyclopropane ring, with the aim to evaluate its substitution with heteroaromatic structures like pyridine and five-terms heteroaromatic rings, leading to molecules characterised by a lower lipophilicity.