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Free Radicals and Antioxidants
Published in Chuong Pham-Huy, Bruno Pham Huy, Food and Lifestyle in Health and Disease, 2022
Chuong Pham-Huy, Bruno Pham Huy
Structurally, the difference between lutein and zeaxanthin is in the type of ionone ring; lutein contains a β-ionone ring and a ε-ionone ring, whereas zeaxanthin has two β-ionone rings. Lutein and zeaxanthin are isomers, but not stereoisomers, which differ in the location of a double bond unsaturation in the end ring (134). Lutein can exist in eight possible stereoisomeric forms because of three chiral centers, but in nature it exists mainly in Z (cis)-form (R,R,R). Zeaxanthin, on the other hand, has two chiral centers but, because of symmetry, exists only in three stereoisomeric forms: (R,R), (S,S), and (R,S-meso) (134). The strong antioxidant activity of lutein and zeaxanthin is due to numerous conjugated double bonds in their lateral chain. Lutein and zeaxanthin are fat-soluble molecules and are generally insoluble in water.
Mephobarbital
Published in Stanley R. Resor, Henn Kutt, The Medical Treatment of Epilepsy, 2020
Mephobarbital (MPB) (5-ethyl-l-methyl-5-phenylbarbituric acid) (la and lb, Fig. 1) is the 1-methyl derivative of phenobarbital (PB) (II, Fig. 1). N-methylation of PB introduces a center of chirality (asymmetry) at carbon-5, and MPB therefore exists as a pair of enantiomers (stereoisomers), R-mephobarbital (la, Fig. 1), which is levorotatory and S-mephobarbital (lb, Fig. 1) which is dextrorotatory (1). The drug is used clinically as the racemate (50% of each enantiomer). As such it is a white crystalline powder, weakly acidic (pK, = 7.8) and somewhat more lipid-soluble than PB.
Chemistry of Essential Oils
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
α-Bisabolol (115) is the simplest of the cyclic sesquiterpenoid alcohols. If farnesol is the sesquiterpenoid equivalent of geraniol and nerolidol of linalool, then α-bisabolol is the equivalent of α-terpineol. It has two chiral centers and therefore exists in four stereoisomeric forms, all of which occur in nature. The richest natural source is Myoporum crassifolium Forst., a shrub from New Caledonia, but α-bisabolol can be found in many other species including chamomile, lavender, and rosemary. It has a faint floral odor and anti-inflammatory properties and is responsible, at least in part, for the related medicinal properties of chamomile oil.
In vitro metabolism assessment of thiacloprid in rainbow trout and rat by LC-UV and high resolution-mass spectrometry
Published in Xenobiotica, 2021
Jose Serrano, Richard C. Kolanczyk, Brett R. Blackwell, Barbara R. Sheedy, Mark A. Tapper
The accurate mass for THI and metabolites TM1, TM2 and TM3, as determined from LC-HR-MS experiments (M + H), was 253.10226, 228.03574, 126.05475 and 128.02740 Da respectively, with all detected structures within a mass error <7 ppm (see Supplemental Tables S5 and S6). Specifically, LC-MS mass chromatograms of THI slice exposures showed the presence of two isomers for both TM1 and TM2 corresponding to the Z-/E-diastereoisomers of TMI (retention times of 1.189 and 1.437 min, respectively), and the enol-/aldehyde-tautomers of TM2 (0.917 and 1.233 min, respectively; Supplemental Table S6). Diastereoisomers are stereoisomers of the same constitution, but the molecules do not have a mirror-image relationship and have different physical and chemical properties. On the other hand, tautomers are molecules with the same molecular formula but different connectivity that are formed in common acid- or base-catalyzed processes.
The application of machine learning techniques to innovative antibacterial discovery and development
Published in Expert Opinion on Drug Discovery, 2020
Mateus Sá Magalhães Serafim, Thales Kronenberger, Patrícia Rufino Oliveira, Antti Poso, Káthia Maria Honório, Bruno Eduardo Fernandes Mota, Vinícius Gonçalves Maltarollo
Recent efforts toward the discovery of new antibiotics follow the direction of predicting potential drug targets for orphan small molecules. The work of Pavel et al. (2019), shows the implementation of PASS models, which are based on Naïve Bayesian models, to assign targets to new input compounds based on the similarity against the tailored curated ChEMBL database [96]. The similarity, as already established in previous versions of the program, is based on molecular descriptors: multilevel neighborhoods of atoms (MNA [97]), which has the limitation of disregarding stereoisomerism and being sensitive to charged compounds. Overall, the PASS method can rank potential targets for compound binding, with disregard for the activity status, not differentiating between agonists/antagonists, for instance. In the newest implementation, the unique ChEMBL identifiers denote different bacteria strains, which can then be further validated experimentally.
Comparative toxicity and toxicokinetic studies of oxiracetam and (S)-oxiracetam in dogs
Published in Xenobiotica, 2019
Tian-tian Liu, Xin-miao Guo, Zu-yuan Rong, Xiang-feng Ye, Jin-feng Wei, Ai-ping Wang, Hong-tao Jin
As a consequence of the rapid advances in chiral synthesis and separation technologies, combined with new regulatory policies for chiral pharmaceuticals, chiral drugs have become an important focus for research and development of new molecular entities (Calcaterra & D'Acquarica, 2018; Nunez et al., 2009; Srinivas, 2004). Stereoisomers (enantiomers and diastereoisomers) not only differ from one another in their pharmacological effects, but also in their pharmacokinetic (adsorption, distribution, biotransformation, and excretion) profiles (Brocks, 2006; Hutt, 2007) and toxicological properties (Natarajan & Basak, 2011; Smith, 2009). Understanding the stereospecificity of in vitro and in vivo pharmacokinetics/toxicokinetics may assist in delineating the developmental path of the racemate and/or the pure enantiomers. The differential actions and toxicities determine enantiomer selection to maximize clinical effects or mitigate drug toxicity. Toxicological evaluation of chiral drugs, therefore, deserves increased attention.