Sensitive detection of topiramate degradation products by high-performance liquid chromatography/electrospray ionization mass spectrometry using ion-pairing reagents and polarity switching

RATIONALE

The chromatographic analysis of topiramate and its degradation products is challenging due to the absence of chromophoric moieties in their structures, the wide polarity range of the compounds and their ionization differences. This work proposes two new mass spectrometry approaches for evaluating these analytes.

METHODS

Based on the calculated experimental limit of detection (LOD), a highly sensitive high-performance liquid chromatography (HPLC) paired-ion electrospray ionization mass spectrometry (PIESI-MS) method was developed for the determination of topiramate inorganic degradation products. The influence of different solvent systems on the LODs for topiramate and its main degradation products was determined in both positive/negative ionization modes. In addition, a HPLC method to analyze both organic and inorganic degradation products was proposed by mass spectrometry with positive/negative ion switching electrospray ionization.

RESULTS

A sensitive HPLC/PIESI-MS method was achieved for the efficient separation of topiramate inorganic degradation products. Both sulfate and sulfamate were detected in the positive selected ion monitoring (SIM) mode with an increased sensitivity compared with the negative SIM mode. The HPLC/ESI-MS analysis with positive/negative ion switching allowed the simultaneous separation and detection of the major degradation products of topiramate in a 10-min run using a single column and a single detector.

CONCLUSIONS

Two new alternative MS approaches for analyzing the main degradation products of topiramate were developed. The proposed methods are considered advantageous over the existing methods and can be applied to quality control studies of topiramate.

Mass spectrometric approaches for the identification of anthracycline analogs produced by actinobacteria

Anthracyclines are a well-known chemical class produced by actinobacteria used effectively in cancer treatment; however, these compounds are usually produced in few amounts because of being toxic against their producers. In this work, we successfully explored the mass spectrometry versatility to detect 18 anthracyclines in microbial crude extract. From collision-induced dissociation and nuclear magnetic resonance spectra, we proposed structures for five new and identified three more anthracyclines already described in the literature, nocardicyclins A and B and nothramicin. One new compound 8 (4-[4-(dimethylamino)-5-hydroxy-4,6-dimethyloxan-2-yl]oxy-2,5,7,12-tetrahydroxy-3,10-dimethoxy-2-methyl-3,4-dihydrotetracene-1,6,11-trione) was isolated and had its structure confirmed by (1) H nuclear magnetic resonance. The anthracyclines identified in this work show an interesting aminoglycoside, poorly found in natural products, 3-methyl-rhodosamine and derivatives. This fact encouraged to develop a focused method to identify compounds with aminoglycosides (rhodosamine, m/z 158; 3-methyl-rhodosamine, m/z 172; 4'-O-acethyl-3-C-methyl-rhodosamine, m/z 214). This method allowed the detection of four more anthracyclines. This focused method can also be applied in the search of these aminoglycosides in other microbial crude extracts. Additionally, it was observed that nocardicyclin A, nothramicin and compound 8 were able to interact to DNA through a DNA-binding study by mass spectrometry, showing its potential as anticancer drugs. Copyright © 2016 John Wiley & Sons, Ltd.

Topiramate: A Review of Analytical Approaches for the Drug Substance, Its Impurities and Pharmaceutical Formulations

An important step during the development of high-performance liquid chromatography (HPLC) methods for quantitative analysis of drugs is choosing the appropriate detector. High sensitivity, reproducibility, stability, wide linear range, compatibility with gradient elution, non-destructive detection of the analyte and response unaffected by changes in the temperature/flow are some of the ideal characteristics of a universal HPLC detector. Topiramate is an anticonvulsant drug mainly used for the treatment of different types of seizures and prophylactic treatment of migraine. Different analytical approaches to quantify topiramate by HPLC have been described because of the lack of chromophoric moieties on its structure, such as derivatization with fluorescent moieties and UV-absorbing moieties, conductivity detection, evaporative light scattering detection, refractive index detection, chemiluminescent nitrogen detection and MS detection. Some methods for the determination of topiramate by capillary electrophoresis and gas chromatography have also been published. This systematic review provides a description of the main analytical methods presented in the literature to analyze topiramate in the drug substance and in pharmaceutical formulations. Each of these methods is briefly discussed, especially considering the detector used with HPLC. In addition, this article presents a review of the data available regarding topiramate stability, degradation products and impurities.

Zwitterionic sulfonates as m/z shift reagents for 5-methylcytosine detection in deoxyribonucleic acids (DNA) using flow injection analysis and electrospray ionization mass spectrometry

5-Methylcytosine (5-MC) is an important epigenetic modification of DNA. Abnormally high concentrations of this substance appear because of the hypermethylation of cytosine. Therefore, the measurement of the quantity of this compound in mammals is of great importance. Recently, we reported that several imidazolium-based zwitterionic sulfonates form complexes with 5-MC in solution, which can be studied by electrospray ionisation mass spectrometry (ESI-MS). It is shown in this paper that such an association can be utilised for the detection of 5-MC in a DNA sample using high-throughput a flow injection analysis ESI-MS method. A variety of the sulfonate zwitterions have been tested as m/z shift reagents to increase the selectivity of the analysis. It is shown that either of the zwitterions can be used without the loss of sensitivity. The performance of the method was tested in terms of linearity range, sensitivity, intra- and between-day precision and accuracy, matrix effect and carryover. The method described is characterised by simplicity, a good limit of quantitation (1 pg injected) and low run times (at least 50 injections per hour). In addition, high-performance liquid chromatography and tandem mass spectrometry are not required. The possibility exists to widen the scope of the method to other amidine-containing compounds present in more complicated matrices.