Oxidative Degradation Products Research Articles

Development and validation of a stability-indicating HPLC assay method for determination of ethacrynic acid in solution formulation. HPLC-MS identification of hydrolytic and oxidative degradation products

An isocratic stability-indicating HPLC assay method was developed to quantitate ethacrynic acid in solution formulations. Utilizing the method, the main hydrolytic, and one of the oxidative degradation products could be separated. The structure of the separated degradation products was confirmed by negative ion-mode HPLC-MS. The hydrolytic results confirmed the previously reported sequence of the formation of the dimeric Michael adduct. One new oxidative metabolite has been identified. The validated analytical method can be used to quantitate ethacrynic acid in a solution formulation in the 0.5-500 µg/ml concentration range.

Methemoglobin determination by multi-component analysis in coho salmon (Oncorhynchus kisutch) possessing unstable hemoglobin

Hemoglobin derivatives are often quantified in blood to establish cardio-respiratory status and possible causes of impaired oxygen transport. The derivative known as methemoglobin results from oxidation of hemoglobin and is pathologically relevant because it cannot transport oxygen. In species and individuals possessing unstable methemoglobin, methemoglobin formation leads to rapid hemichrome formation and precipitation. Oxidizing reagents in standard methemoglobin analysis techniques therefore prevent accurate quantification of hemoglobin oxidative degradation products in species possessing unstable hemoglobin. In this study, we demonstrated that individual coho salmon (Oncorhynchus kisutch) possess unstable methemoglobin. Because molar absorptivities of coho methemoglobin, hemichrome and carboxyhemoglobin were significantly different from humans, the use of previous standard methods leads to an overestimation of methemoglobin in coho. Spontaneous conversion of methemoglobin to hemichrome was also demonstrated in Chinook (O. tshawytscha), pink (O. gorbuscha) and chum salmon (O. keta), but not steelhead (O. mykiss), indicating there may be a frequent need to account for unstable hemoglobin when quantifying methemoglobin in salmonids.•Our method builds upon multi-component analysis (MCA) by using a multivariate modeling technique to derive the coho-specific molar absorptivities of major hemoglobin derivatives•This approach fills a current need for the accurate quantification of methemoglobin in fishes possessing unstable hemoglobin

Identification and Characterization of Forced Degradation Products for Dofetilide using Rapid and Sensitive UPLC-MS/MS Method and HRMS Studies

A simple, rapid and efficient method has been developed and validated using ultra UPLC combined with Q-ToF MS system for recognition and characterization of forced degradation products obtained from dofetilide degradation studies. The dofetilide drug is an antiarrhythmic and belongs to Class III and it was treated with various stress conditions like acidic, basic, oxidative, photolytic and thermal conditions as per ICH guidelines. The main drug shows extensive degradation towards oxidative degradation conditions and single degradation product was identified through chromatogram. The chromatographic separation among main and its impurities were attained through 2.1 × 150, 1.8 μm column from gradient elution using UPLC and its detection at wavelength 230 nm. The validation was performed for the developed method using various parameters like specificity, linearity and robustness studies. Waters Synapt G2 Q TOF system was used and performed MSn studies to establish mass spectral fragmentation pathway for drug and its degradation products and determined accurate masses study. The efficiency of this method was helpful to identify and characterize the drug and degradation products using LC/MSn techniques.

Stress Degradation Studies of Riociguat, Development of Validated Stability Indicating Method, Identification, Isolation and Characterization of Degradation Products by LC-HR-MS/MS and NMR Studies

Abstract: Aim: The present study reports the degradation behavior of new antihypertensive drug Riociguat under various stress conditions as per International Conference on Harmonization guidelines ICH, Q2(R1). Materials and Methods: Riociguat was subjected to stress degradation under hydrolytic (acidic, alkaline and neutral), oxidative, photolytic and thermal stress conditions to investigate the inherent stability. A rapid, accurate, precise and robust HPLC method was developed on Waters Symmetry C18 Column (150mm X 4.6 mm, 5μ) using isocratic elution of 10 mm ammonium acetate buffer pH 5.7 and acetonitrile in the ratio of 70:30 with the flow rate at 1.0 mL/min.The detection was performed at 254nm. Results: The drug was found to be degraded in alkaline and oxidative condition whereas it was stable under acidic, neutral hydrolytic, thermal and photolytic conditions. Two degradation products (DP1, DP2) under alkaline condition and one under oxidative condition (DP3) were characterized by LC-HR-MS/MS with accurate mass measurements. Degradation products (DP1, DP2 and DP3) were isolated by preparative HPLC and were characterized by 1H NMR, 13C NMR, APT and IR Techniques. Conclusion: Using spectral data analysis, alkaline degradation product DP1 wascharacterized as 2-(1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl)-N5-methylpyrimidine-4,5,6-triamine and DP2 was characterized as 2-(1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl)- 6-amino-7-methyl-7H-purin-8(9H)-one while oxidative degradation product DP3was characterized as methyl 2-(1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl)-4,6- diaminopyrimidin-5-ylmethylcarbamate-N-oxide.The developed chromatographic method was validated in terms of specificity, linearity, accuracy, precision as per ICH guidelines. The robustness of the method was studied with 2-level fractional factorial design 2^4-1. Key words: Riociguat, Stress degradation, RP-HPLC, LC-HR-MS/MS, Preparative HPLC, NMR.

Stress Degradation Studies on Bimatoprost and Development of Validated Stability Indicating Densitometric RP-TLC and HPLC Methods

Simple, sensitive and accurate stability-indicating densitometric RP-TLC and RP HPLC-UV methods were developed and validated for analysis of Bimatoprost (BMT). Stress stability studies were performed using hydrolytic (acid & alkai) and oxidative degradation products and conformed using LC-MS. Structure elucidation and pathway of degradation were presented. Both methods were based on reversed phase thin-layer and liquid chromatographic separation of BMT from hydrolytic and oxidative degradation products. Acetonitrile, water and 33% ammonia (4:5:1, by volume) and acetonitrile –water (40:60, v/v) at 30◦C were used as mobile phases for separation of BMT from degradation products using RP TLC and HPLC methods respectively. Quantification was achieved at 220 nm for both methods. The linear ranges were 0.5-6.0 μg/band and 5 – 100 μg /mL with mean recoveries ± RSD%, of 98.72 ± 0. 31% and 99.25 ± 0.59% for the two methods respectively. The specificity of HPLC method was further assured by peak purity. The proposed methods are rapid with retention time less than 6 min. The methods met ICH regulatory requirements. The two methods were successfully applied for the quantification of BMT in drug substance and ophthalmic solution with acceptable accuracy and precisions; the label claim percentages were 93.145 ± 0.89 and 95.35 + 0.65 for densitometric RP-TLC and RP HPLC-UV methods respectively. The research work has a great value for quality control and stability studies of BMT.

Curcumin induces secretion of glucagon-like peptide-1 through an oxidation-dependent mechanism

Curcumin shows antiglycemic effects in animals. Curcumin is chemically unstable at physiological pH, and its oxidative degradation products were shown to contribute to its anti-inflammatory effects. Since the degradation products may also contribute to other effects, we analyzed their role in the antiglycemic activity of curcumin. We quantified curcumin-induced release of glucagon-like peptide 1 (GLP-1) from mouse STC-1 cells that represent enteroendocrine L-cells as a major source of this anti-diabetic hormone. Curcumin induced secretion of GLP-1 in a dose-dependent manner. Two chemically stable analogues of curcumin that do not readily undergo degradation, were less active while two unstable analogues were active secretagogues. Chromatographically isolated spiroepoxide, an unstable oxidative metabolite of curcumin with anti-inflammatory activity, also induced secretion of GLP-1. Stable compounds like the final oxidative metabolite bicyclopentadione, and the major plasma metabolite, curcumin-glucuronide, were inactive. GLP-1 secretion induced by curcumin and its oxidative degradation products was associated with activation of PKC, ERK, and CaM kinase II. Since activity largely correlated with instability of curcumin and the analogues, we tested the extent of covalent binding to proteins in STC-1 cells and found it occurred with similar affinity as N-ethylmaleimide, indicating covalent binding occurred with nucleophilic cysteine residues. These results suggest that oxidative metabolites of curcumin are involved in the antiglycemic effects of curcumin. Our findings support the hypothesis that curcumin functions as a pro-drug requiring oxidative activation to reveal its bioactive metabolites that act by binding to target proteins thereby causing a change in function.

Determination of flibanserin in the presence of confirmed degradation products by a third derivative emission spectrofluorometric method: Application to pharmaceutical formulation.

Flibanserin is a new drug used for the treatment of hypoactive sexual desire disorder. This work is considered the first study concerning the fluorimetric behaviour of flibanserin and its new florescent degradation products. A fast, cost-effective, stability-indicating spectrofluorometric method was developed and validated for the determination of flibanserin in the presence of oxidative degradation products. Stability studies are performed to predict the behaviour of substances under various harsh conditions. Thus, flibanserin was subjected to degradation using hydrogen peroxide. The stability-indicating method was developed and validated per ICH guidelines; it was linear in the range of 0.1-3 μg/mL. The method was accurate and precise as it showed good recoveries between 98.50 and 100.90% and relative standard deviation less than 2%, respectively, and no significant differences were found after statistical comparison with the in-house HPLC method. In addition, the structures of the oxidative degradation products were confirmed using infrared spectroscopy and mass spectrometry, and the proposed degradation pathway was predicted.

Validated Stability Indicating HPTLC, UHPLC and UV-Spectrophotometric Techniques for the Determination of Bepotastine Besilate in Presence of Its Oxidative Degradate

The study is aimed at developing methods which have a complete validation as stipulated in the ICH guidelines and to be applied for the determination of Bepotastine besilate (BB) in pure form and in pharmaceutical formulations in the presence of its oxidative degradation product. High performance thin layer chromatography (HPTLC), Ultra high performance liquid chromatography (UHPLC) and different spectrophotometric methods (first derivative, first derivative of ratio spectra and ratio difference are developed for simultaneous determination of bepotastine besilate in laboratory-prepared mixtures of bepotastine besilate with its oxidative degradate and in pharmaceutical formulations were used in the study design. Firstly, HPTLC was performed and separation occurred on silica gel 60 F254 plates, with butanol: ammonia (8:2, v/v) as a developing system. UHPLC in which separation occurred on a Kinetex C 18 column using methanol- 0.1% O-phosphoric acid - acetonitrile (70:20:10, by volume) as mobile phase, followed. And lastly was UV/Vis spectrophotometry which included first derivative determination of the drug at 252.6 nm, first derivative of ratio of peak amplitudes at 233.4, 250 and 275.6 nm and the ratio difference with the amplitude difference between (240 nm and 260 nm). Result showed that HPTLC method was applicable over the concentration range of 0.5-5 μg / band, while UHPLC method was linear over the concentration 2- 12 μg/mL and spectrophotometric methods were linear over the concentration range 20-120 μg/mL for bepotastine besilate. The proposed three techniques are quite accurate and precise. They can be used for routine analysis of bepotastine besilate in pharmaceutical formulation and stability indicating methods.

Utility of a green fluorone-based turn-off fluorescence probe for submicromolar determination and stability testing of two macrolides. Insights into reaction thermodynamics, quenching mechanism, and identification of the oxidative degradation products by ESI+-MS

A smart, sensitive, and green turn-off fluorescence probe was developed and validated for the determination of two macrolides; spiramycin (SPM) and josamycin (JSM) at submicromolar concentration levels. The probe is based on the fluorone-based dye, eosin Y that efficiently interacts with the two compounds through ground-state ion-pair complex formation with quenching of its native fluorescence (λex/λem of 524/548 nm). The Stern-Volmer relationship confirmed the static fluorescence quenching mechanism. Furthermore, the thermodynamic parameters of the reaction were explored via the van't Hoff plot. The values of the fluorescence quenching were linearly correlated to the drug concentration over the ranges of 0.12–5.93 and 0.30–9.66 μM (0.1–5.0 and 0.25–8.0 μg/mL) for SPM and JSM, respectively. Therefore, the probe was utilized for quality control of the two compounds in their tablets with mean %recoveries of 98.12 ± 1.72 and 97.22 ± 1.51% for SPM and JSM, respectively. Statistical analysis of the results by t- and F-tests showed excellent agreement with the results of the comparison methods. Moreover, the developed probe was applied for stability testing of the two compounds under oxidative condition along with ESI+-MS identification of the potential degradants. Besides, the greenness of the developed probe was ensured by different assessment metrics. Hence, the developed method is the first stability-indicating fluorimetric assay for the two compounds, and its chief merits include effortlessness, rapidness, sensitivity, cheapness and harmony with the green chemistry rules.

Waste of Optical Fiber — Raw Material Base of Secondary Germany

Utilization of optical fiber involves two problems: the use of a protective shell (mainly various types of plastics) and the actual optical fibersquartz filaments with an admixture of germanium dioxide coated with a protective layer of polyethylene. The aim of the work was to study the physical and chemical properties of samples of optical fiber wastes. The behavior of the components of this material has been studied by thermography: a quartz germanium-containing glass and a polyethylene sheath during heat treatment. It has been established that in the temperature range from 20 to 700 °С in the atmosphere of the air quartz fiber does not undergo changes, and the polyethylene shell of the optical fiber passes through the stages of sorption of water vapor and air oxygen at 125 and 200 °С during melting, and above 300 °С – destruction with a mass loss of up to 55 % and the release into the gas of products of oxidative degradation.

Stability Indicating Spectrophotometric and Chemometric Methods for Determination of Aripiprazole in Presence of its Degradation Products, A Comparative Study

Simple, accurate, selective and validated stability indicating UV spectrophotometric univariate and multivariate methods were developed for determination of Aripiprazole in presence of its alkaline and oxidative degradation products. The developed univariate methods; derivative ratio spectra-zero crossing, successive derivatives of ratio spectra and mean centering of ratio spectra. The first one used the amplitude of the first derivative ratio signals at 303.0 nm, the second method depended on the successive derivative of ratio spectra in two steps and measuring the absorbance of Aripiprazole at 281.0 nm and the third one measured the mean centered values oat 294.0 nm. Two chemometric multivariate methods were applied; principal component regression (PCR) and partial least-squares regression (PLS). The selectivity of the proposed methods was confirmed using laboratory-prepared mixtures. The obtained results were statistically compared with those obtained with the manufacturer HPLC method, showing no significant difference with in accuracy and precision. These methods could be applied as stability indicating methods for the determination of Aripiprazole in presence of its degradation products, in bulk powder or in pharmaceutical formulations.

Direct screening of food packaging materials for post-polymerization residues, degradation products and additives by liquid extraction surface analysis nanoelectrospray mass spectrometry (LESA-nESI-MS)

Materials in direct contact with food should be monitored for the presence of species able to migrate into food. A direct method based on liquid extraction surface analysis nanoelectrospray mass spectrometry (LESA-nanoESI-MS) was developed for the analysis of the migrating species from a polymer film. Different types of molecules: post-polymerization residues, degradation products (oligomers resulting from polymer recycling, products of polymer oxidative degradation) and anti-oxidant additives (vitamin E) were demonstrated to be detected and identified, and determined quantitatively if relevant calibration standards are available. The method was validated by a comparison a standard method based on with bulk extraction mass spectrometry. It offers considerable advantages over the latter in terms of drastically reduced analysis time and solvent consumption. Also, LESA-nanoESI-MS produced simpler spectra (limited to compounds able to migrate into food) than Direct Analysis in Real Time (DART).

Serum Oxidative-Antioxidative Status in Patients With Alkaptonuria

BackgroundAlkaptonuria (AKU) is a rare genetic disease associated with the deposition of melanin-like pigments (ochronosis) in connective tissues. However, data regarding the effect of oxidative stress products on disease pathogenesis are limited. The purpose of this study was to investigate oxidative stress and related factors in patients with alkaptonuria and compare the findings with those in healthy control subjects.MethodsThe study sample comprised of 21 AKU patients and 19 age- and sex-matched healthy controls. Serum samples were obtained to detect the total antioxidative capacity (TAC), and oxidation degradation products of thiobarbituric acid-reactive substances, protein carbonyls, advanced oxidation protein products, and homogentisic acid levels in urine were determined.ResultsSerum TAC, oxidation degradation products of thiobarbituric acid-reactive substances, and protein carbonyl levels in the AKU group were higher than those measured for the control subjects, and the difference was statistically significant (P < 0.05). Moreover, a positive correlation was found between the patient’s serum protein carbonyl, patient’s age and AKU severity score (r = 0.492 and 0.746, respectively; P < 0.05). Furthermore, the protein carbonyl serum levels can be used to predict the disease severity score in alkaptonuria patients (P < 0.05).ConclusionsIn sum, the study results provide further support for the role of oxidation in the pathogenesis of alkaptonuria, suggesting presence of a more complex relationship than what has been previously assumed. Thus, further studies are needed to clarify these conflicting results.

Degradation kinetics and mechanism of 3-Chlorobenzoic acid in anoxic water environment using graphene/TiO2 as photocatalyst

ABSTRACT Degradation kinetics and mechanism of 3-Chlorobenzoic acid (3-CBA) in anoxic water environment using graphene/TiO2 (GR/TiO2) as photocatalyst had been investigated. The effects of various parameters such as catalyst dosage, pH, initial concentration, catalyst reuse and dissolved oxygen (DO) on 3-CBA photocatalytic degradation kinetics were studied. The qualitative and quantitative analysis for degradation intermediate products and parent compound were studied by using HPLC, HPLC/MS/MS and IC technologies. The results show that the residual concentration of 3-CBA has a good linear relationship and its correlation coefficient R 2 are all greater than 0.985 by Langmuir–Hinshelwood (L–H) dynamic model under different photocatalytic degradation conditions. Some oxidative degradation products such as 3-chlorophenol, resorcinol, and hydroxyquinol are generated, and some reductive degradation products such as 3-chlorobenzaldehyde, 3-hydroxybenzaldehyde, 3-hydroxybenzyl alcohol, and cyclohexanediol are produced, and part of 3-CBA are mineralized to generate CO2 when DO is in the range of 0.5–1.0 mg/L; When DO is less than 0.28 mg/L, photocatalytic reduction mainly occurs. The results provide a theoretical basis for photocatalytic in situ remediation of pollutants in anoxic water environment.

Diabetes and obesity during pregnancy are associated with oxidative stress genotoxicity in newborns.

Objective To compare the level of oxidative deoxyribonucleic acid (DNA) damage (genotoxicity) between the offspring of mothers with and without diabetes diagnosed during pregnancy and its association with maternal body mass index (BMI). Methods We measured 8-hydroxy-deoxyguanosine (8-OH-dG), a marker of DNA oxidative damage, in venous umbilical cord plasma from newborns of mothers with (n=34) and without (n=56) diabetes diagnoses obtained during pregnancy. Two markers of oxidative stress - namely, nitric oxide degradation products (NOx) and total glutathione (GSH) - were quantified in both mothers and newborns. The effects of BMI, glycated hemoglobin (HbA1c), age and delivery mode were also analyzed. Results Newborns of mothers with diabetes during pregnancy exhibited higher levels of 8-OH-dG than those of mothers without diabetes (P<0.001). The other markers of oxidative stress were also higher in both mothers with diabetes and their newborns, with the exception of NOx in the mothers. The association of diabetes with 8-OH-dG was independent of other analyzed factors. Conclusion The offspring of mothers with diabetes during pregnancy are born with increased genotoxicity than the offspring of mothers without diabetes. BMI and HbA1c display an independent association with 8-OH-dG, particularly in the offspring of mothers not diagnosed with diabetes.

Enzymatic and non-enzymatic pathways of kynurenines' dimerization: the molecular factors for oxidative stress development.

Kynurenines, the products of tryptophan oxidative degradation, are involved in multiple neuropathologies, such as Huntington's chorea, Parkinson's disease, senile dementia, etc. The major cause for hydroxykynurenines's neurotoxicity is the oxidative stress induced by the reactive oxygen species (ROS), the by-products of L-3-hydroxykynurenine (L-3HOK) and 3-hydroxyanthranilic acid (3HAA) oxidative self-dimerization. 2-aminophenol (2AP), a structural precursor of L-3HOK and 3HAA, undergoes the oxidative conjugation to form 2-aminophenoxazinone. There are several modes of 2AP dimerization, including both enzymatic and non-enzymatic stages. In this study, the free energies for 2AP, L-3HOK and 3HAA dimerization stages have been calculated at B3LYP/6-311G(d,p)//6-311+(O)+G(d) level, both in the gas phase and in heptane or water solution. For the intermediates, ionization potentials and electron affinities were calculated, as well as free energy and kinetics of molecular oxygen interaction with several non-enzymatically formed dimers. H-atom donating power of the intermediates increases upon the progress of the oxidation, making possible generation of hydroperoxyl radical or hydrogen peroxide from O2 at the last stages. Among the dimerization intermediates, 2-aminophenoxazinole derivatives have the lowest ionization potential and can reduce O2 to superoxide anion. The rate for O-H homolytic bond dissociation is significantly higher than that for C-H bond in non-enzymatic quinoneimine conjugate. However, the last reaction passes irreversibly, reducing O2 to hydroperoxyl radical. The inorganic ferrous iron and the heme group of Drosophila phenoxazinone synthase significantly reduce the energy cost of 2AP H-atom abstraction by O2. We have also shown experimentally that total antioxidant capacity decreases in Drosophila mutant cardinal with L-3HOK excess relative to the wild type Canton-S, and lipid peroxidation decreases in aged cardinal. Taken together, our data supports the conception of hydroxykynurenines' dual role in neurotoxicity: serving as antioxidants themselves, blocking lipid peroxidation by H-atom donation, they also can easily generate ROS upon dimerization, leading to the oxidative stress development.

Different Mathematical Spectrophotometric Methods for Determination of Lesinurad in the Presence of its Oxidative Degradation Product

Lesinurad is a novel selective uric acid reabsorption inhibitor which has been recently approved for the treatment of the chronic gout. Four simple mathematical spectrophotometric methods have been developed for the quantitative and selective determination of lesinurad in the presence of its oxidative degradation product. Complete oxidative degradation of lesinurad to its degradation product has been done. The developed methods namely, ratio difference spectrophotometric, first derivative of the ratio spectra, mean centering of the ratio spectra and continuous wavelet transform spectrophotometric methods. These methods have been developed and optimized to resolve the existed overlapping between the zero order UV absorption spectra of lesinurad and its oxidative degradation product. The described spectrophotometric methods have achieved selective determination of lesinurad without any interference from the oxidative degradation product. Also, they have been validated and applied for quantitative analysis of the studied drug in its new pharmaceutical preparation.

Enrichment of Relevant Oxidative Degradation Products in Pharmaceuticals With Targeted Chemoselective Oxidation

The ability to produce and isolate relatively pure amounts of relevant degradation products is key to several aspects of drug product development: (a) aid in the unambiguous structural identification of such degradation products, fulfilling regulatory requirements to develop safe formulations (International Conference on Harmonization Q3B and M7); (b) pursue as appropriate safety evaluations with such material, such as chronic toxicology or Ames testing; (c) for a specified degradation product in a late-stage regulatory filing, use pure and well-characterized material as the analytical standard. Producing such materials is often a resource- and time-intensive activity, either relying on the isolation of slowly formed degradation products from stressed drug product or by re-purposing the drug substance synthetic route. This problem is exacerbated if the material of interest is an oxidative degradation product, because typical oxidative stressing (H2O2 and radical initiators) tends to produce a myriad of irrelevant species beyond a certain stress threshold, greatly complicating attempts for isolating the relevant degradation product. In this article, we present reagents and methods that may allow the rapid and selective enrichment of active pharmaceutical ingredient with the desired oxidative degradation product, which can then be isolated and used for purposes described above.

Stress Degradation Studies of Anagliptin, Development of Validated Stability Indicating Method, Degradation Kinetics Study, Identification and Isolation of Degradation Products

A gradient-specific stability indicating HPLC method was developed and validated for the determination of the antidiabetic agent anagliptin in laboratory mixtures. Reversed-phase chromatography was performed using a Shimadzu LC-20 AD pump (binary), Shimadzu PDA M-20A diode array detector, and Waters Symmetry C-18 column (150 × 4.6 mm, 3.5 µm) maintained at a column oven temperature of 40 °C with UV detection at 247 nm. A gradient program was run at flow rate of 1 mL min−1. Mobile phase A consisted of a mixture of acetate buffer(10 mm) pH 5/methanol/acetonitrile in the ratio of 90:5:5. Mobile phase B consisted of a mixture of acetate buffer (10 mm) pH 5/methanol/acetonitrile in the ratio of 50:25:25. The method was validated according International Conference of Harmonization (ICH) guidelines. Linearity was observed in the concentration range of 10–120 µg/mL with regression coefficient r2(0.999). The LOD was found to be 7.8 µg/mL and LOQ was found to be 22.68 µg/mL. Anagliptin was subjected to stresses such as acidic, alkali, oxidation, photolysis, and thermal conditions. The proposed method was validated as per ICH guidelines and was found to be accurate, precise, and specific. The drug showed significant degradation in alkaline and oxidative conditions. Alkaline and oxidative degradation followed first-order kinetics. Degradation rate constant and half-lives were determined. Degradation products in alkaline and oxidative conditions were identified by LC–MS. One major degradation product was isolated from each condition by preparative HPLC. These degradation products were characterized by 1H NMR, 13C NMR, DEPT, D2O exchange, MS/MS, HRMS, and IR techniques. From the spectral data the alkaline degradation product was characterized as 1-{2-[1-(2-methylpyrazolo[1,5-a]pyrimidine-6-carboxamido)-methyl-propan-2-yl-amino]acetyl}pyrrolidine-2-carboxamide. The oxidative degradation product was characterized as N-[2-({2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl}amino)-2-methylpropyl]-2-methylpyrazolo-[1,5-a]pyrimidine-N-oxido-6-carboxamide.

Epoxy Composites Filled with Sodium Bicarbonate: Thermal and Mechanical Properties

The epoxy composites filled with 5 and 10 mass % of sodium bicarbonate were prepared. Sodium bicarbonate at the heating decomposes into sodium carbonate, carbon dioxide and water. As a result, sodium bicarbonate is able to slow down the combustion process when it used as polymer filler. The thermal stability of the prepared samples was investigated at the heating in air using thermal analysis. The mechanical characteristics of epoxy composites were also studied. The gaseous products of thermal oxidative degradation were studied using mass spectrometric analysis. It was found that sodium bicarbonate accelerates the process of thermal oxidative degradation of the epoxy composites in the initial stage, but enhances thermal stability in the final stage. The addition of boric acid to sodium bicarbonate as filler is recommended to improve the thermal stability of the epoxy polymer.