Vundavilli Jagadeesh Kumar

Identification, isolation and characterization of process related impurities in ezetimibe

During the synthesis of ezetimibe, two process related impurities were detected were HPLC analysis at levels ranging from 0.05 to 0.8%. These two impurities were isolated by column chromatography and co-injected with ezetimibe sample to confirm the retention times in HPLC. These two impurities were characterized as 2-(4-hydroxybenzyl)-N,5-bis(4-fluorophenyl) pentanamide (impurity-I) and 1-(4-fluorophenyl)-3(3-(4-fluorophenyl)propyl)-4-(4-hydroxyphenyl)azetidin-2-one (impurity-II). Isolation, structural elucidation of these impurities by spectral data ((1)H NMR, (13)C NMR, MS and IR) and probable mechanism of their formation have been discussed.

Stability indicating ion chromatography method for the simultaneous determination of ibandronate sodium drug substance and its impurities.

A simple and sensitive ion chromatography method has been developed for the simultaneous assay of ibandronate sodium drug substance and the determination of its impurities. The separation was achieved on Allsep™ anion column 150 mm × 4.6 mm, 7 μm particle diameter. The mobile phase consisted of 1% (v/v) aqueous formic acid and acetone 98:2% (v/v); flow rate 1.0 ml min(-1) at ambient temperature. The analytes were monitored by conductometric detector. The drug substance was subjected to stress conditions of hydrolysis, oxidation, photolytic, thermal and humidity degradation. Considerable degradation was achieved only under oxidative conditions. Mass balance was demonstrated in all stress conditions. The method was validated for specificity, precision, linearity, solution stability and accuracy. The limits of detection (LOD) and limits of quantification (LOQ) for impurities were in the range of 0.36-0.80 μg ml(-1) and 1.00-2.40 μg ml(-1), respectively. For ibandronate LOD was 38 μg ml(-1) and LOQ was 113 μg ml(-1). The average recoveries for impurities and ibandronate were in the range of 99.0-103.1% and the method can be successfully applied for the routine analysis of ibandronate sodium drug substance.

X-ray K-absorption edge shifts due to chemical combination

A possible explanation is given of the chemical shifts of x-ray K-absorption edges of metals when they undergo a chemical combination and form compounds. It is proposed that when a metal forms a compound its Fermi edge changes. It explains the numerical order as well as the nature of the chemical shifts. A fairly good agreement between the calculated and observed values has been obtained.

Identification, isolation and characterization of a new degradation product in sultamicillin drug substance

A new degradant of sultamicillin drug substance was found during the gradient reverse phase HPLC analysis of stability storage samples. The level of this degradant impurity was observed up to 1.0%. The impurity (formaldehyde adduct with 5-oxo-4-phenylimidazolidin-1-yl moiety) was identified by LC/MS and was characterized by ((1)H NMR, (13)C NMR, 2D-NMR ((1)H-(1)H COSY, NOESY, HSQC and HMBC), LC/MS/MS, MS/TOF, elemental analysis and IR. This impurity was prepared by isolation and co-injected into HPLC system to confirm the retention time.

Identification, isolation and characterization of a new impurity in cefoxitin drug substance resulting from stress stability studies

A new unknown impurity of cefoxitin formed during a gradient reverse phase high performance liquid chromatography (HPLC) analysis of stress stability samples of the drug substance cefoxitin, and the level of this impurity was found at up to 0.9%. This impurity was identified by LC-MS and characterized by (1H NMR, 13C NMR, LC/MS/MS, elemental analysis and FT-IR). Based on the spectral data, the impurity was named as, 3-[[(2R,3S)-[3-methoxy-3-N-[2-(thiophen-2-yl)acetamido]]-4-oxoazetidin-2-ylthio]-2-[(carbamoyloxy)methyl]]-acrylic acid. The structure of this impurity was also established unambiguously, prepared by isolation and co-injected into HPLC to confirm the retention time. To the best of our knowledge, this impurity has not been reported elsewhere. Structural elucidation of the impurity by spectral data is discussed in detail.