Pharmaceutical and related drugs

Raman and IR spectroscopic studies of fenamates--conformational differences in polymorphs of flufenamic acid, mefenamic acid and tolfenamic acid

Solid-state Raman and IR spectra of two polymorphic forms of each of three fenamates (flufenamic acid, mefenamic acid and tolfenamic acid) display subtle but highly reproducible differences. Many of these spectral differences can be ascribed to different conformations of these molecules, involving two of four possible orientations of one substituted benzene ring with respect to the other. Interpretation of the vibrational spectra in terms of conformational differences has been facilitated by DFT calculations at the B3LYP/cc-pVDZ level for each conformer. The calculated spectra are compared with the experimental spectra in order to identify the conformers present in two polymorphic forms in each case, and detailed band assignments are obtained from the DFT calculations.

Optimization of a multiresidual method for the determination of waterborne emerging organic pollutants using solid-phase extraction and liquid chromatography/tandem mass spectrometry and isotope dilution mass spectrometry

A high-throughput, liquid chromatography/tandem mass spectrometry (LC/MS-MS) method has been developed for the determination of 51 emerging organic pollutants (EOPs) in environmental waters. The method was validated for the analysis of 38 pharmaceutically active, 10 endocrine disrupting, and three perfluoroalkylated compounds. Method performance parameters, including sample preservatives, pH values used in the solid-phase extraction (SPE), sample storage, sample extract storage time, and matrix effects were discussed in detail for different aquatic matrices, including drinking water, wastewater, and surface water. Isotope-labeled compounds were used as injection internal standards (IIS) or isotope dilution quantitation standards (IDQS) to improve the data quality, investigate the behavior of matrix effects during SPE sample preparation and LC/MS-MS analysis, and to validate isotope dilution mass spectrometric (IDMS) determination of selected compounds. Method detection limits were determined to be in the low ng/L range forthe compounds evaluated. By application of this method to the analysis of effluents and samples downstream of a wastewater treatment plant, more than 35 target EOPs were quantified. We demonstrated method ruggedness by quality control and quality assurance (QC/QA) data, showed that matrix effects were dependent on modes of electrospray ionization, and could not be removed via SPE or cleanup procedures, exerting the same effect to target compounds in both raw and extracted samples. Both 13C- and 2H-labeled IDQS could be added to samples before sample extraction, and their recoveries used to correct matrix effects in LC/MS-MS EOP analyses.

Infrared studies of the polymorphic states of the fenamates

Infrared spectroscopy has been used to characterize the polymorphic purity as well as to study the thermal conversion of three of the more common fenamates between their different crystalline forms via measuring changes in the NH stretch region that occur between 3300 and 3350 wavenumbers. Shifts in band frequency for mefenamic acid result from differences in internal hydrogen bonding between the NH group and either the carbonyl or hydroxyl groups of the acid moiety. Due to out-of-plane rotations about the central N-C(ring2) bond additional polymorphic states have been suggested for flufenamic and tolfenamic acids. Rates of conversion are given for flufenamic, mefenamic, and tolfenamic acids at temperatures between 85 and 160 degrees C depending on the polymorphic transition for a particular analyte. Subsequently, these rates are used to calculate the activation energy for the observed polymorphic transition. Values of 71.6, 49.0, and 50.8 kcal/mol are obtained respectively for (1) the polymorph I to II transition of mefenamic acid, (2) the polymorph I to II transition of tolfenamic acid, and (3) the polymorph III to I transition of flufenamic acid.