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Publications (17)
A concept of a systematic approach to the development of phase appropriate RP-HPLC methods for quantifying organic impurities in Active Pharmaceutical Ingredients (APIs) is presented. This dynamic and practical approach emphasizes the utilization of comprehensive chromatographic knowledge gained throughout the lifecycle of drug development based on...
Many pharmaceutical genotoxic impurities are neutral molecules. Trace level analysis of these neutral analytes is hampered by their poor ionization efficiency in mass spectrometry (MS). Two analytical approaches including chemical derivatization and coordination ion spray-MS were developed to enhance neutral analyte detection sensitivity. The chemi...
Pharmaceutical regulatory agencies are increasingly concerned with trace-level genotoxic impurities in drug substances, requiring manufacturers to deliver innovative approaches for their analysis and control. The need to control most genotoxic impurities in the low ppm level relative to the active pharmaceutical ingredient (API), combined with the...
3-Alkylthio- (or 3-arylthio-)pyridines and 3,5-bis(alkylthio)pyridine can be conveniently prepared by the reaction of 3-thiocyanato- or 3,5-bis(thiocyanato)pyridines with tri-n-butylphosphine in the presence of alcohol.
Derivatization LC/MS methodology has been developed for the determination of a group of commonly encountered alkyl esters of sulfonates or sulfates in drug substances at low ppm levels. This general method uses trimethylamine as the derivatizing reagent for ethyl/propyl/isopropyl esters and triethylamine for methyl esters. The resulting quaternary...
Evaporative light scattering detection (ELSD) is an inexpensive “universal” mode of optical detection for LC. We report here on ELSD as a useful adjunct to UV detection for the RP-HPLC peptide mapping of proteins. We use peptide mapping as a “finger-printing” technique to detect post-translational modifications and other small changes to recombinan...
Using a 10 m×0.1 mm I.D. DB-624 capillary column, fast separation of 40 commonly used solvents can be achieved in a single analysis in less than 4.9 min. For typical determination of trace solvents in drug substance, the analysis time can further be shortened to less than 1.5 min using combined temperature and pressure programming. The technique wa...
Using dual detection with UV and evaporative light scattering detectors, a gradient LC-MS-compatible method was successfully developed for the separation and identification of impurity and degradates in mupirocin in a complex matrix containing 98% (w/w) of polyethylene glycol (PEG) 400 and PEG 3350. The method enabled the eluent containing the PEGs...
Racemic SK&F 106203 and its homologues can be directly separated on Chiralcel OD, Chiralpak AD and AS columns. The corresponding dimethyl esters, however, can only be resolved on the Chiralcel OD column. Hydrogen bonding between the carboxylic acid proton of the analyte and the chiral stationary phase appears critical for chiral recognition on Chir...
Enantiomeric peptidoleukotriene antagonists, SK&F R-106203 and SK&F S-106203 can be effectively separated on a cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase. The utility of this chiral high-performance liquid chromatographic method in assigning absolute stereochemistry to SK&F S-106203-Z2, a non-crystalline amorphous compound...
A method for the chromatographic separation and detection of 3-methyl-4,5-dihydro-1,2,3-oxadiazolium (MDO) ion has been developed. Convenient retention times were obtained on a reversed-phase LC column by using the ion-pairing reagent 1-octanesulfonic acid in phosphate buffer as the mobile phase. The cyclic voltammogram of the analyte showed an irr...
Dihydrohalide salts of pharmaceutical compounds effect reduction of dimethyl sulfoxide to give dimethyl sulfide under mild conditions. The reduction was initiated by the facile dissociation of HCl or HBr from the dihydrohalide salts and involved α-chloromethyl (or α-bromomethyl) methyl sulfide and α-chloromethyl (or α-bromomethyl) methyl sulfoxide...
An ammonia gas sensor was used to determine 5′-nucleotidase in serum through the ammonia produced from the coupled reactions of 5′-nucleotidase and adenosine deaminase. Nonspecific hydrolysis of the substrate 5′-adenosine monophosphate by serum alkaline phosphatase was corrected for by using the inhibitor concanavalin A. The present method is fast...
2-Chloro-3-thiocyanatopyridine reacted with thioacetic acid and thiobenzoic acid to yield 2-acetylimino-1,3-dithiolo[4,5-b]pyridine and 2-benzoylimino-1,3-dithiolo[4,5-b]pyridine respectively. 2,5,6-Trihalo-3-thiocyanatopyridine under the same conditions gave only the corresponding 3-S-acetyl-3-thio or 3-S-benzoyl-3-thiopyridine.
Six triterpenoids have been isolated from leaves of the tropical tree Cordia alliodora (Boraginaceae) and assigned structures on the basis of spectral and crystallographic data and chemical interconversions. All six compounds, 3α-hydroxyolean-12-en-27-oic acid and five oxidized derivatives, were found to be significantly ant repellent in a bioassay...
Controlled chlorination of 2,6-diaminopyridine (1) affords 2,6-diamino-3,5-dichloropyridine (2a) which is then bis(diazotised) to give 2,3,5,6-tetrachloropyridine (3a); similarly prepared are other 2,3,5,6-tetra(chloro/bromo)pyridines and 2,6-dichloro-3,5-bis(thiocyanato)pyridine (3h), from which 3,5-bis(alkylthio)pyridines are easily obtained.