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Application of Asymmetric Catalysis to the Synthesis of Peptide Mimics
Published in John R. Kosak, Thomas A. Johnson, Catalysis of Organic Reactions, 2020
John J. Talley, Cathleen E. Hanau, Gary A. DeCrescenzo, Michelle A. Schmidt
Inasmuch as peptide molecules possess biochemical information in their primary, secondary, and tertiary structure, one is forced to use chiral isos-teres in order to convey this information. It is now widely recognized that many drugs containing stereogenic centers effect their biological response in the form of a single stereoisomer. Our efforts have sought to take advantage of the wealth of knowledge accumulated at Monsanto on asymmetric catalysis as a cornerstone of our research into the synthesis and evaluation of peptide isosteres. Asymmetric catalysis frequently offers certain allowances over different procedures of asymmetric synthesis including the following: (1) the reaction is catalytic, (2) one is not restricted to the chiral pool, (3) optical inductions tend to be high, (4) the processes are quite general and high-yielding, and (5) the use of chiral auxiliaries is obviated. A discussion of asymmetric methodology for the preparation of 2-substituted succinic acids, α-substituted β-amino acids, and β-substituted β-amino acids, will be presented and some of their applications.
Stereochemistry
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
When two different molecules have the same empirical formula, and they are isomers. If those molecules have the same formula but different connectivity, they are constitutional isomers. If those molecules have the same empirical formula and the same connectivity (all atoms are attached to the same atoms), but they differ in their spatial arrangement about a given atom or point in the molecule, they are called stereoisomers. In other words, stereoisomers are isomers with the same empirical formula, the same constitution (the same connectivity), but a different arrangement of atoms in space. The two different molecules 2-bromo-2-chlorobutane and the mirror image discussed in a previous question are stereoisomers. Which of the following molecules have a stereogenic center?
Magnetic Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Tsourkas et al. (2004) developed a homogeneous enantioselective immuno-sensor that utilizes magnetic relaxation switching (MRS). An enantiomer is one of two stereoisomers that are mirror images of each other. “Enantioselective” relates to a chemical reaction in which one enantiomer of a chiral product (a molecule that is not superimposable on its mirror image) is preferentially produced. The enantioselective MRS immunosensor was based on magnetic nanoparticles labeled with a derivative of d-phenylalanine (d-Phe), C9H11NO2, a form of the essential amino acid, l-phenylalanine, that, when taken as a supplement, protects the body’s production of naturally occurring painkillers.
Effective control of optical purity by chiral HPLC separation for ester-based liquid crystalline materials forming anticlinic smectic phases
Published in Liquid Crystals, 2021
Terézia Vojtylová-Jurkovičová, Petra Vaňkátová, Magdalena Urbańska, Věra Hamplová, David Sýkora, Alexej Bubnov
Chirality, based on molecular symmetry elements, is present in many regular systems in nature [1], and it is widely used in artificially designed systems as part of smart functional organic materials utilised in various applications. Enantiomers (or stereoisomers) can exhibit significantly diverse properties in chiral environment. Moreover, there is growing evidence that chirality can also induce unique characteristics of artificially designed materials and devices [2,3] based on such materials. In reality, starting materials and intermediates available for the synthesis of chiral substances are often not perfectly optically pure. In most cases, a low percentage of the opposite enantiomer (impurity) is present. Moreover, a partial racemisation of the intermediates during a specific synthetic step can be another considerable source of the optical purity decrease. In the past, optical purity was determined primarily by optical rotation measurements, which does not allow obtaining sufficiently accurate information on trace amounts of the pollutant stereoisomer. In many cases, the enantiomeric purity of the compounds was not documented in the literature or with insufficient precision and accuracy.
Metabolic engineered E. coli for the production of (R)-1,2-propanediol from biodiesel derived glycerol
Published in Biofuels, 2022
Wilson Sierra, Pilar Menéndez, Sonia Rodríguez Giordano
The stereochemistry of the obtained product is determined by the enzyme that acts on the C2 of methylglyoxal (2) (Gre2p). Based on previous literature reports on the stereochemistry of this enzyme, production of the stereoisomer with the (R) configuration was expected [66]. The likely contribution of Ypr1p on C2 carbonyl reduction does not pose a challenge to the stereochemical outcome, since this enzyme usually follows Prelog’s rule too [66, 67]. This fact was confirmed experimentally, chiral GC analysis and co-injection with authentic optically pure standards, allowed us to assign the product as (R)-1,2-propanediol (4a) with an enantiomeric excess greater than 99% (Figure S3, SM).
A new advance in the potential exposure to “old” and “new” halogenated flame retardants in the atmospheric environments and biota: From occurrence to transformation products and metabolites
Published in Critical Reviews in Environmental Science and Technology, 2020
Shengtao Ma, Yingxin Yu, Yan Yang, Guiying Li, Taicheng An
Based on this review, the atmospheric occurrence of several typical of “old” and “new” HFRs were included and new advance were demonstrated in detail. Their potential transformation products in the environment and biota were also summarized. Although research on transformation products have attracted more attention recently, the identification of transformation products is still rarely confirmed, and the potential metabolism pathways of these potential toxicity compounds also requires further research in the near future. Specific suggestions for further research are listed below.More HFRs, as well as their transformation products, should be include in routine monitoring at regional and global scale, especially in densely populated areas. Systematic continuous-time trends studies are also urgently needed for hotspot sites, for example, to monitor toxic substance emissions from e-waste recycling regions, especially to investigate the unusually elevated levels of DBDPE and BDE-209 in air particles from mega-center such as Guangzhou of southern China.Sensitive and specific analytical methods are also highly needed, for example, LC-based methods should be further developed to investigate the dechlorination products of DP, as well as the debromination products of BDE-209 and DBDPE. Stereoisomer analysis may become an invaluable tool to study the isomer-specific susceptibility to the degradation intermediates of some HFRs, such as DP and HBCD, and to further improve our understanding of the congener-specific fate of these chemicals, which in turn will provide insights into their biotransformation behavior in biota.Synthesis and purification methods for the congener specific authentic standards of HFRs as well as related transformation products are urgently needed. The identification and quantification of these transformation products are completely dependent on the availability of reference standards. The lack of commercially available standards significantly hinders the discovery of potential transformation products and could subsequently delay the further understanding of possible transformation mechanism.Toxicological studies of these transformation products also need to be considered using multidisciplinary approaches, especially in instances where the metabolites may be more biologically active than their parent compounds. For example, the combination strategy of experimental data (in vitro and in vivo) with computational theoretical results can provide a more comprehensive assessment of toxic effects of transformation products. In addition, it would be increase certainty if the isotope labeled standards were used during the transformation processes.