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Chemistry of Essential Oils
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
Many enzymes need cofactors as reagents or energy providers. Coenzyme-A has already been mentioned earlier. It is a thiol and is used to form thioesters with carboxylic acids. This has two effects on the acid in question. First, the thiolate anion is a better leaving group than alkoxide and so the carbonyl carbon of the thioester is reactive toward nucleophiles. Second, the thioester group increases the acidity of the protons adjacent to the carbonyl group and therefore promotes the formation of the corresponding carbanions. In biosynthesis, a key role of adenosine triphosphate (ATP) is to make phosphate esters of alcohols (phosphorylation). One of the phosphate groups of ATP is added to the alcohol to give the corresponding phosphate ester and adenosine diphosphate. Another group of cofactors of importance to biosynthesis includes pairs such as NADP/NADPH, TPN/TPNH, and DPN/DPNH. These cofactors contain an N-alkylated pyridine ring. In each pair, one form comprises an N-alkylated pyridinium salt and the other the corresponding N-alkyl-1,4-dihydropyridine. The two forms in each pair are interconverted by gain or loss of a hydride anion and therefore constitute redox reagents. In all of the cofactors mentioned here, the reactive part of the molecule is only a small part of the whole. However, the bulk of the molecule has an important role in molecular recognition. The cofactor docks into the active site of the enzyme through recognition, and this holds the cofactor in the optimum spatial configuration relative to the substrate.
Affinity Modification — Organic Chemistry
Published in Dmitri G. Knorre, Valentin V. Vlassov, Affinity Modification of Biopolymers, 1989
Dmitri G. Knorre, Valentin V. Vlassov
This intermediate was found to be readily oxidized by suitable electron acceptors such as hexacyanoferrate [Fe3+(CN)6]3_. In the course of the oxidation of the carbanion intermediate, the enzyme is inactivated. The exact reason for the inactivation is not yet elucidated.
Steroid Carboxylic Acids
Published in Ronald Hobkirk, Steroid Biochemistry, 1979
A similar epimerization is noted at position 20 with 17,20-acetonides of 17,20-dihydroxy-21-oic acid methyl esters.241 Synthesis of these derivatives occurs by oxidation of the 21-alcohol of the 17,20-acetonide derivatives of the 17,20,21-triols or directly from 17,20-dihydroxy acids.242 The 17,20α-acetonide 21-methyl ester is converted to a 3:1 mixture of 17,20β- and 17,20α-acetonide-21-oic acids by refluxing with excess alkali. The probable mechanism involves the loss of a proton from C-20 to yield a carbanion. As a consequence, asymmetry at C-20 is abolished by the formation of a resonance hybrid. Readdition of a proton occurs with the formation of the sterically favored 20β acetonide.
Understanding the structural insights of enzymatic conformations for adenylosuccinate lyase receptor in malarial parasite Plasmodium falciparum
Published in Journal of Receptors and Signal Transduction, 2021
Malaria is a disease caused by the intracellular, protozoan parasites of the genus Plasmodium and through this work, the plasmodium falciparum enzyme structure of adenylosuccinate lyase is examined with react and product. The reaction mechanism of the adenylosuccinate catalytic mechanism switch to AMP and fumarate proceeds via a general acid/base mechanism in which the C-beta proton atom of the substrate is modified by the general base (thought to be serine), yielding a carbanion intermediate. As of now, Plasmodium falciparum adenylosuccinate lyase is an important enzyme in purine metabolism and there have been several studies explain the reaction mechanism, this study focuses to clear the atomic insights of reactant and product. Most of the docking and simulation works are processed with AMP bound adenylosuccinate lyase, and the complex is showing high deviations, that may result in unbound state of drugs. Adenylosuccinate bound complex involves His role in the product than the reactant complex, and the complex shows high flexibility due to fumarate. Thus, the identifying the core inhibitor, that bounds to His rings, possibly an aromatic feature processed compound could be a standard adenylosuccinate lyase inhibitor, that can block the malarial diseases in human.
New generation of viral nanoparticles for targeted drug delivery in cancer therapy
Published in Journal of Drug Targeting, 2022
Nikta Alvandi, Maryam Rajabnejad, Zeynab Taghvaei, Neda Esfandiari
Bioconjugation is a kind of functionalisation of amino acid chains (Figure 4(E)) with chemical components, for example, it was reported that reactive amines were conjugated on lysine residues (Lysine-N-hydroxysuccinide chemistry) or sulfhydryl groups on cysteine residues (Cystenine-maleimide chemistry) or even carboxylate groups were conjugated on glutamic and aspartic acid residues (Carboxylate-carbodiimide chemistry). These aforementioned functionalisation kinds along with click chemistry are common methods for modifying VLPs (Figure 5). In detail, N-hydroxysuccinimide (NHS)-activated esters that are identified as a linker on lysine side chains can link any compatible molecule with NHS chemistry [21]. In this way, NHS as an activating reagent can play a significant role in carboxylic acids activation. These activated acids can react with amines and convert them to amides (Figure 5(A)) [44]. It is noteworthy to mention the common difference between NHS and Sulfo-NHS as similar linkers. Activation with NHS declines water solubility of modified carboxylate molecule, whereas Sulfo-NHS increases it by charged sulphonate group. Furthermore, as shown in Figure 5(B), the linkage between maleimides and sulfhydryl groups of cysteine residues can be considered as Michael reaction. It should be mentioned that Michael reaction is the addition of carbanion as a nucleophilic compound to α, β-unsaturated carbonyl component containing an electron-withdrawing group [45]. The penultimate group of common conjugation of VLPs is carbodiimide coupling agents with the formula of RN = C=NR that can link any molecule like a primary amine to the carboxylate groups of glutamic and aspartic acid [21] that this group can be categorised into four subcategories, namely DCC, DIC, EDC, and CMC (Figure 5(C)). The last group of usual VLPs conjugation is devoted to click chemistry (Figure 5(D)). This is the class of biocompatible molecules reactions utilised in bioconjugation and have some advantages, such as high yield, easy purification, and being versatile. Generally, click chemistry is defined as the one-pot process that comprises powerful linking reactions that are simple to perform [46]. Click reaction can be classified into four classifications, namely cycloadditions, nucleophilic ring-openings, carbonyl chemistry of the non-aldol type, and additions to carbon-carbon multiple bonds. Among these four categories, the most consumption rate accounts for cycloadditions, especially Cu-catalyzed Huisgen 1,3-dipolar cycloaddition (HDC) of azides and terminal alkynes to form 1,2,3-triazoles (Figure 5(D)) [46]. Nowadays, new methods have been utilised to incorporate click reaction, namely unnatural amino acids that comprise reactive groups into proteins and nucleotides modification.