China
Africa
Explore chapters and articles related to this topic
Battlefield Chemical Inhalation Injury
Published in Jacob Loke, Pathophysiology and Treatment of Inhalation Injuries, 2020
Phosgene was originally thought to be toxic to the lung through the mechanism of hydrolysis and production of topically toxic (hydrochloride) HC1. Subsequent studies suggest that this is not the case since free inhaled HC1 is approximately 1/800 times as toxic as phosgene (Buscher, 1931) and ketene, a substance with a similarly available carbonyl group (but that does not hydrolyze to HC1), is almost equally as toxic as phosgene.
Mass Spectrometric Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
Positive and negative ion spectra were obtained from five penicillins using desorption CI [233]. The positive ion spectra were obtained using ammonia and exhibited protonated molecular ions with 0.5−18% relative abundance. Both products from a 2 + 2 cycloreversion process (Scheme 1) were observed, as were other previously reported fragmentation products [234]. The ammonium adduct of the ketene cycloreversion product is also present. The methane negative ion spectra exhibit M− and (M − H)− ions, cycloreversion product ions (Scheme 1), and two processes not previously reported. These appear to derive from losses of hydrogen sulfide and carbon dioxide in one step and loss of carbon monoxide in a subsequent step (Scheme 2). In some spectra ions derived from the former process are too short-lived to be apparent.
Influence of Light on Essential Oil Constituents
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
Marie-Christine Cudlik, Gerhard Buchbauer
This hydrogen atom shift had lower threshold energy in isoeugenol than eugenol (308 nm vs. 285 nm). In both cases, it resulted in the generation of two types of long-chain conjugated ketenes, depending on where the hydrogen atom repositioned itself on the ring. In another step of reaction, decarbonylation of the ketenes took place (Krupa et al., 2012).
A review on synthetic chalcone derivatives as tubulin polymerisation inhibitors
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Wenjing Liu, Min He, Yongjun Li, Zhiyun Peng, Guangcheng Wang
The relative position of the two aryl rings in chalcone plays a crucial role in the activity of the binding tubulin, which allows the ketene bridge to be modified. It has been reported that hydrogenation or bromination significantly reduces chalcone activity through carbon-carbon double bonds or halogenation or conversion to corresponding epoxides. Therefore, the double bond in the ketene structure may be the key site affecting the bioactivity of the compound. However, when the double bond of chalcone remains unchanged, it is unstable in vivo due to its ability to undergo Michael addition reactions with biological nucleophiles. Thus, the researchers substituted the ketene-bridge double bond with a heterocyclic ring, which not only maintained the relative tertiary stability of the two aryl rings but also avoided nucleophilic reactions in vivo, thus improving the stability of chalcones88.
Acetylenes: cytochrome P450 oxidation and mechanism-based enzyme inactivation
Published in Drug Metabolism Reviews, 2019
Direct evidence that oxidation of the triple bond involves reaction of the oxygen with one of the acetylenic π-bonds rather than insertion into the acetylenic C–H bond is provided by the finding that when the acetylenic proton of 4-ethynylbiphenyl is replaced by a deuterium, the deuterium migrates quantitatively to the adjacent carbon in the acetic acid product. Loss of deuterium would be expected for C–H hydroxylation. Furthermore, when the biphenyl-substituted carbon is 13C-labeled, the 13C-labeled carbon remains attached to the biphenyl in the product. These results establish that the hydrogen rather than the biphenyl is the moiety that migrates during the oxidative process. In addition, a substantial deuterium isotope effect is observed on the rate of ketene formation upon replacement of the acetylenic hydrogen by a deuterium (Ortiz de Montellano and Komives 1985; Komives and Ortiz de Montellano 1987). Finally, the ketene oxygen has been shown in the case of biphenylacetylene to derive from molecular oxygen, in accord with oxygen transfer from a cytochrome P450 enzyme (Ortiz de Montellano and Komives 1985). The same hydrogen shift has been shown to occur when the triple bond is chemically oxidized by meta-chloroperbenzoic acid. In the chemical experiments, direct evidence for formation of the ketene was provided by isolation of the methyl ester rather than free acid when the oxidation was carried out in the presence of methanol (Ortiz de Montellano and Kunze 1980a, 1981a).
N-terminal α-amino group modification of antibodies using a site-selective click chemistry method
Published in mAbs, 2018
De-zhi Li, Bing-nan Han, Rui Wei, Gui-yang Yao, Zhizhen Chen, Jie Liu, Terence C.W. Poon, Wu Su, Zhongyu Zhu, Dimiter S. Dimitrov, Qi Zhao
The N-terminal α-amine is a crucial site of protein post-translational modification that affects protein activation, conversion, and degradation.22 The α-amine has gained attention for in vitro protein modification. In addition, N-terminal serines or threonines can be oxidized to aldehydes and react with amines and alkoxyamine groups.23-26 Recent studies showed that the α-amine of proteins can be modified through ketene without interfering with side chains.27 Nevertheless, the labile property of ketene makes its synthesis difficult. A recent study showed that 2-pyridinecarboxyaldehyde (2-PCA) formed a stable imidazolidinone with N-terminal amines of protein under mild conditions.28 Although the above-mentioned methods are of great interest, they have several limitations, including difficulties in chemical synthesis, unwanted byproducts, and low reaction efficiency. Therefore, a simple and mild method for coupling a small molecule onto a natural amino acid of peptides or proteins with high selectivity is needed.