Fragmentation of diamide derivatives of 3,4-ethylenedioxythiophene.

The sequential product ion (MS(n)) fragmentation of four symmetric diamide derivatives of 3,4-ethylenedioxythiophene were characterized using ion trap mass spectrometry with electrospray ionization and their fragmentation patterns were studied. The experimental data consists of mass spectra obtained by tandem mass spectrometry, and calculations were obtained by the M06-2X/6-31 G (d,p) method. Investigated compounds represent building blocks in synthesis of compounds used in different areas of chemistry and industry such as in medicinal chemistry, as potential anticancer and anticonvulsant agents, in organic chemistry as linkers for solid-phase synthesis, and in the synthesis of a variety of materials in polymer chemistry. We present herein the investigation of the fragmentation pathway of protonated diamide derivatives of 3,4-ethylenedioxythiophene that involves the identification of fragments, influence of proton transfer on direction of fragmentation and mechanisms of reactions by which the fragmentation process occurs. Data obtained from product ion spectra of these protonated compounds and density functional theory (DFT) calculations indicate that the fragmentation process takes place via four main reactions: amido-iminol proton transfer, reverse cycloaddition, cleavage of the amide bond, and isocyanic acid elimination. The 3,4-ethylenedioxythiophene-2,5-dicarboxamide was observed as an intermediate in the fragmentation of its alkyl derivatives. To our knowledge, this work brings the first correct description of the mechanism of elimination of isocyanic acid.

Xenobiotic clenbuterol in food producing male pigs: Various tissue residue accumulation on days after withdrawal.

Using enzyme-linked immunosorbent assay (ELISA) and liquid chromatography tandem mass spectrometry (LC-MS/MS) the concentrations of clenbuterol (ng/g) were shown to be highest in choroid/pigmented retinal epithelium (choroid/PRE) (499.59±26.36ng/g), followed by hair (fair colored) (207.76±86.88ng/g), liver (25.06±16.72ng/g) and kidney (6.88±3.52ng/g) after 28 days of oral clenbuterol administration in a growth-promoting dose (10µg/kg BW, twice daily) to food producing male pigs, with a high correlation coefficient between the two methods for all study matrices (r=0.8800-0.9999). In the liver as an alimentary tissue and regulatory matrix for the control of clenbuterol abuse, the maximal allowed concentration of 0.5ng/g was achieved in liver tissue (0.40±0.12ng/g) on day 14 and in the kidney (0.28±0.10ng/g) on day 7 after treatment withdrawal. In contrast, the concentration of residual clenbuterol in choroid/PRE (57.49±6.13ng/g) and hair (68.36±3.35ng/g) recorded on day 14 of withdrawal was 143- and 170-fold that measured in the liver, with a similar ratio persisting on day 35 of withdrawal (164:1 and 183:1, respectively). These findings indicated a high accumulation potential of clenbuterol residues in the hair and choroid/PRE as compared with the liver and kidney, pointing to the pig choroid/PRE and hair as useful new matrices in the control of clenbuterol abuse as a growth promotant in food production, especially after prolonged withdrawal.

The application of LC-NMR and LC-MS for the separation and rapid structure elucidation of an unknown impurity in 5-aminosalicylic acid.

This work has demonstrated the usefulness of combining liquid chromatography-nuclear magnetic resonance spectroscopy (LC-NMR) and liquid chromatography-mass spectrometry (LC-MS) methodologies for a rapid identification of an unknown impurity (N1) in the drug 5-aminosalycilic acid. Complementary information obtained from the two methods has revealed plenty of structural information and led to the fast on-line structure determination of N1 prior to its isolation and purification. The analysis of LC-NMR and LC-MS spectra revealed that N1 and 5-aminosalycilic acid are structurally closely related compounds. The structure of N1 was later confirmed by high-resolution NMR spectroscopy of the isolated compound and the atom assignment was made. The approach described here has potential for 5-aminosalycilic acid impurity profiling and monitoring the production process.

LC-NMR and LC-MS identification of an impurity in a novel antifungal drug icofungipen.

Successful use of LC-NMR and LC-MS for rapid identification of an impurity in a novel antifungal drug icofungipen has been demonstrated. Complementary information obtained from the two methods made it possible to determine the structure of A1 prior to its isolation and purification. Stop-flow LC-NMR ((1)H and DQFCOSY), LC-MS and LC-MS/MS spectra have shown that A1 is structurally related to icofungipen. It was later isolated and prepared synthetically and its structure was corroborated by high-resolution NMR spectroscopy.