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Gas Chromatographic Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
Despite the very wide use of tetracyclines for years, there are very few reports on their analysis by GC. This clearly indicates the difficulty involved. Tsuji and Robertson [35] did report a method for chlorotetracycline, Degradation of lasalocid by “thermolizing.” (From Ref. 34.)doxycycline, oxytetracycline, tetracycline, 4-epi-tetracycline, and 4-epi- anhydrotetracycline. The silylation, with freshly prepared BSA plus TMCS dissolved with internal standard (trioctanoin) in pyridine, took 24 hr at room temperature. Higher temperatures caused degradation. Mass spectrometric data indicated that there were five silyl substitutions per tetracycline molecule.
Production, Extraction and Characterization of Alginates from Seaweeds
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
Faiez Hentati, Alina V. Ursu, Guillaume Pierre, Cedric Delattre, Bogdan Trica, Slim Abdelkafi, Gholamreza Djelveh, Tanase Dobre, Philippe Michaud
Gaz Chromatography coupled with Mass Spectrometry and Electron Ionization (GC/MS-EI) is another method for determining M/G ratios of hydrolyzed alginates (trifluoroacetic acid 2 M, 90 min, 120°C) after derivatization of their constitutive uronic acids (Hentati et al. 2018). Silylation using BSTFA (Bis (trimethysilyl) trifluoroacetamide) and TMCS (trimethylchlorosilane) reagents (99:1–90:10) is the most common method used at various temperatures (from ambient temperature to 80°C) and reactions times (30 to 240 min). Trimethylsilyl-O-glycosides into dichloromethane can be separated for example into a OPTIMA-1MS column eluted with a helium flow rate (Hentati et al. 2018).
Radiochemistry for Preclinical Imaging Studies
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Otherwise, tin (trialkylstannyl), silicon (trialkylsilyl), and boron (boronic acid) substituents have been incorporated in the precursor as leaving groups for radioiodination (Coenen et al. 2006; Adak et al. 2012). Accordingly, these reactions are called iodo-destannylation, iodo-desilylation, and iodo-deboronation. Still, to introduce these groups in the first place, the arene substrate usually needs to be activated. The subsequent iodination step, however, can be done at milder conditions and with high regiospecificity.
An overview of late-stage functionalization in today’s drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Michael Moir, Jonathan J. Danon, Tristan A. Reekie, Michael Kassiou
The functionalization of aryl C–H bonds with main group reagents such as silanes and boranes occurs with unique regioselectivity dictated by the catalyst used. The obtained compounds are useful intermediates for further functionalization and diversification. The silylation of aryl C–H bonds is less developed than the corresponding borylation reactions. Despite their synthetic utility, reactions for the catalytic silylation of C–H bonds generally require harsh reaction conditions, excess of reagents and/or directing groups. Cheng and Hartwig have reported a method for the iridium catalyzed reaction of HSiMe(OSiMe3)2 and (hetero)arenes with high levels of sterically driven regioselectivity (Figure 4(c)) [46]. The silylation of a series of pharmaceutical compounds including clonidine (87% yield) demonstrates the applicability of this method for LSF.
Metabolomics reveals the depletion of intracellular metabolites in HepG2 cells after treatment with gold nanoparticles
Published in Nanotoxicology, 2018
Jeremie Zander Lindeque, Alnari Matthyser, Shayne Mason, Roan Louw, Cornelius Johannes Francois Taute
For untargeted GC-MS analysis, the dried cell extracts were oximated with the addition of 50 µl methoxyamine hydrochloride (2 mg/ml pyridine). After 1 h incubation at 50 °C, the samples were allowed to cool down for 5 min before adding a silylation agent. One hundred microliters of N,O-Bistrifluoroacetamide (BSTFA) with 1% trimethylsilyl chloride (TMCS) were added to each sample and incubated again at 50 °C for 1 h. GC-MS analyses were performed on a GC-TOF-MS system which consisted of an Agilent 7890 A GC front-end system and a Leco Pegasus HT TOFMS with an Agilent 7693 autosampler. The samples were separated with an RTX-1 MS column (30 m × 250 µm × 0.25 µm) from Restek. Two microliters of the sample was injected in splitless mode. Helium was used as a carrier gas with a constant flow rate of 1.5 ml/minute. The front inlet temperature remained 250 °C during injection. The GC oven initiated at a temperature of 70 °C for 1 min, after which the temperature was increased stepwise to 120 °C at 7 °C/min, then again increased to 230 °C at 10 °C/min, and finally increased to 300 °C at 13 °C/min. The GC oven remained 300 °C for 1 min before cooling down and returning to its initial temperature. The transfer line remained at a constant temperature of 225 °C and the source remained 200 °C. Electron impact ionization was performed at −70 V to fragment the compounds that eluted. An acquisition delay of 450 s was allowed before the data was acquired at 20 spectra/s (50–950 m/z).
Metabolism of cyclic phenones in rainbow trout in vitro assays
Published in Xenobiotica, 2020
Jose Serrano, Mark A. Tapper, Richard C. Kolanczyk, Barbara R. Sheedy, Tylor Lahren, Dean E. Hammermeister, Jeffrey S. Denny, Michael W. Hornung, Alena Kubátová, Patricia A. Kosian, Jessica Voelker, Patricia K. Schmieder
Efforts were made to search for metabolites of CPK in trout liver slice exposures. Despite the lack of metabolites detected for CPK in binding cytosols, the rapid decline in the amount of CPK/well in the presence of slices (Figure 2(c)), and the slice Vtg induction noted by Tapper et al. (2018b), indicated that metabolites were likely present. In fact, CPK yielded over 13 potential metabolites by 4 h of slice exposures, with none identified as CPKOH or opCPK for which Stds were available. Therefore, additional methods were necessary to characterize CPK metabolite structures as reported at length in Serrano et al. (2019). Nine of 13 possible metabolic products (labeled CPK M1–M9; cyclohexenyl-, cyclohexanone- and cyclohexanol-derivatives of CPK), could be readily characterized and measured in slice media above LOD. The low abundance of the other products prevented further characterization. The labels, structures, general classification and physical/experimental properties for the CPK metabolites identified in slice exposures are summarized in Table 3. Surprisingly, mass spectrometric evidence supported an apparent preference for metabolic modification of the cyclohexyl ring for all CPK metabolites characterized instead of a phenyl ring modification as predicted by metabolism models (Kolanczyk et al., 2012). Furthermore, chemical derivatization with silylation reagents supported that M6–M9 contained a hydroxyl group. As previously stated, there were no Stds available for M1–M9; therefore, it was not possible to directly quantify their concentrations in the slice or media. Thus, alternative strategies for semi-quantitation of M1–M9 in hexane extracts were applied (see Data analysis). Additional efforts were performed to measure the potential appearance of hydrophilic metabolites in aqueous fractions (see Supplemental Information). No evidence of any parent chemicals or metabolites was found in aqueous fractions of media or slice lysate analyzed by HPLC or LC-MS.