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A synthesis route for stable isotope-labeled sulfamethoxazole-benzene ring-13C6 has been developed. In this strategy, 13C6-benzene was used as the source and starting material for stable isotope labeling and starting material to synthesize sulfachloropyridazine-benzene ring-13C6 through 6 steps of nitration, nitroreduction, acylation, sulfonation, condensation and hydrolysis. The product structure was confirmed through characterization techniques such as nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS), which the purity of the product was higher than 98.0% and the isotopic enrichment was higher than 99.0atom%13C. Sulfachloropyridazine-benzene ring-13C6 can be used as an internal standard reagent for qualitative and quantitative analysis of sulfachlorpyridazine.

In order to improve the stable isotope utilization rate, a simple and inexpensive synthesis method was developed. The synthesis of levofloxacin is based on piperazine as the starting material, and the reaction with carbobenzoxy chloride (CBZ-Cl) to get CBZ-piperazine-CD3, and then the reaction with iodomethane-D3 to get CBZ-piperazine-CD3, after the removal of CBZ protection to get methylpiperazine-D3, and finally the reaction with levofloxacin carboxylic acid to get levofloxin-D3. The yield of levofloxacin-D3 was 37.0% based on the amount of iodomethane-D3. The synthesized Levofloxacin-D3 product was characterized by nuclear magnetic resonance spectroscopy, high performance liquid chromatography and mass spectrometry. The chemical purity was 98.5% and the isotope abundance was 99.5atom% D. It can be used as the internal standard for the quantitative determination of levofloxacin residue in animal food.

Copyright of Journal of Isotopes is the property of Journal of Isotopes Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Isotopes is the property of Journal of Isotopes Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Post-translational modification of proteins is complex and diverse, with the phosphorylation regulated by kinases and phosphatases being one of the most widespread and important modifications. Dynamic change of quantitative analysis of phosphorylated proteins is helpful to clarify the mechanism of phosphorylation regulating life activities and understand its role in achieving biological functions. Mass spectrometry is the most commonly used strategy for the quantitative analysis of post-translational modification, involving label-free quantification, internal standard absolute quantification, and chemical labeling, etc. In this paper, a chemical labeling approach which has been used for protein glycosylation profiling was applied to the relative quantitative analysis of phosphopeptides. Using the method, carboxyl groups were located on the side chain of aspartic acid and glutamic acid residues, and the C-terminus of peptide were allowed to react with dimethylamine (d0-DMA)/deuterated dimethylamine (d6-DMA). As a result, the carboxyl groups were neutralized, and all enzymatic peptides were labeled with light/heavy tags. After the samples with different tags were mixed, the phosphopeptides were enriched using TiO2 magnetic particles and then analyzed qualitatively and relatively quantitatively by liquid chromatography-mass spectrometry (LC-MS). Amidation could shield the negatively charged carboxyl groups of non-phosphorylated and phosphorylated peptides, so that the peptides with phosphate groups mainly exhibited negative charge property, thus improving the enrichment specificity of TiO2 for phosphopeptides as well as its detection sensitivity in LC-MS analysis. Using 0.2 mg casein as a standard, 8 phosphopeptides were detected in the derivatized samples. A high abundance of b and y ions indicated that the amidation by dimethylamine was highly specific and usually occurs only at the carboxyl group without a significant effect on the phosphate group of peptides. A series of molar ratios (5∶1, 2∶1, 1∶1, 1∶2, 1∶5) of samples were derivatized using d0-DMA and d6-DMA, respectively. The results showed that the error was less than 20% for each ratio, indicating that the method possessed good relative quantitative range and accuracy. However, too many derivative sites in the peptides could result in incomplete derivatization, and the C-terminal lysine residues might self-condense to form lactam during the derivatization process. By selecting some individualized proteases during protein digestion, such as GluC, the number of derivative sites might be in an appropriate range and lysine residue could be avoided at the terminal of peptides, which should be useful for improving identification efficiency and quantitative accuracy of phosphopeptides. In summary, the chemical labeling method based on dimethylamine derivatization presents advantages for high-throughput relative quantitative analysis of phosphopeptides and it is expected to be a powerful tool for protein phosphorylation profiling in biological tissues. [ABSTRACT FROM AUTHOR]

In order to study the effects of straw C on the contents of dissolved organic carbon（DOC）, microbial biomass carbon（MBC）and particulate organic carbon（POC）in low-fertility soil at different nitrogen application rates, 13C-labeled wheat straw was mixed with low fertility soils in the carborundum tube at different nitrogen application rates（0, 120, 240 kg·hm-2, pure nitrogen content）. Soils were sampled periodically to analyze carbon component contents and its relative δ13C value. Straw C transformation rate and contribution to soil C pool was also calculated. The results showed that straw C was transformed rapidly within the first 7 days, thereafter the decomposition rate slowed down and was dependent on transformation to POC. Compared with DOC, straw C preferred transforming into MBC and POC, with the transformation rate of 0.12%~0.38%, 4.01%~6.25% and 4.74%~9.54% on 60 d after straw addition, respectively. Soil DOC, MBC, and POC contents were increased significantly by straw addition, with 0.29%~15.01%, 13.20%~32.85% and 33.62%~59.69% of respective carbon derived from straw, respectively. Compared with 0, 240 kg·hm-2 application rates, 120 kg hm-2 could increase the active and slow organic C pool of the experimental soil simultaneously. All results suggest that straw return with moderate nitrogen application is more conducive to both soil fertility improvement and C sequestration of low fertility soil. [ABSTRACT FROM AUTHOR]

Liver cancer is the fifth most common cancer with extremely low five year survival rate. Early diagnosis is of great importance for cancer therapy. In this work, stable isotope labeling-based relative quantitative proteomics and parallel reaction monitoring-based target proteomics were combined for cancer biomarker screening and validation. By using this strategy, 70 significantly changed proteins in hepatocellular carcinoma tissues were obtained, among which seven proteins were further validated. The validated proteins contain the clinically used hepatocellular carcinoma (HCC) biomarker alpha-fetoprotein (AFP) and the reported biomarker candidates Heat shock protein HSP 90-beta (HSP90), fatty acid-binding protein, epidermal (FABP5) and alcohol dehydrogenase 4 (ADH4), which demonstrated the robustness of the strategy. The proteins identified in this work could be benefit for further HCC biomarker screening and clinical validation. Moreover, this strategy could be further applied to other cancer types.