Mechanistic study of enantiomeric recognition with native gamma-cyclodextrin by capillary electrophoresis, reversed-phase liquid chromatography, nuclear magnetic resonance spectroscopy, electrospray mass spectrometry and circular dichroism techniques.

The possible mechanisms for the chiral recognition of 2(S)-(3,5-bis-trifluoromethyl-phenyl)-2-[3(S)-(4-fluorophenyl)-4-(1H-[1,2,4]triazol-3-ylmethyl)-morpholin-2(R)-yloxy]-ethanol (compound A) and its enantiomer with native gamma-cyclodextrin (gamma-CD) were investigated using capillary electrophoresis (CE), reversed-phase liquid chromatography (RPLC), proton (1H), fluorine (19F) and carbon (13C) nuclear magnetic resonance spectroscopy (NMR), electrospray mass spectrometry (ESI-MS) and circular dichroism (CD). All experiments provided clear evidence of the formation of diastereomeric complexes between the enantiomers and gamma-CD. Proton, fluorine and carbon NMR spectra suggested that both aromatic rings, with mono-fluoro and bis-tri-fluoro functional groups, on the guest molecule were partially included into the cavity of the gamma-CD. ESI-MS spectra indicated that the diastereomeric complexes have a 1:1 stoichiometric ratio. The binding constants of the diastereomeric complexes obtained by CE, RPLC and CD were compared. The effects of the gamma-CD concentration, organic modifiers and temperature on the CE-chiral separation were also investigated.

Examination of rofecoxib solution decomposition under alkaline and photolytic stress conditions.

Rofecoxib is a highly active and selective cyclo-oxygenase II inhibitor. A stability-indicating method for the assay of rofecoxib has been developed using reverse-phase high-performance liquid chromatography (HPLC). Stress testing of rofecoxib was conducted during the method development and validation. HPLC analysis of rofecoxib solutions stressed under alkaline and photolytic conditions revealed the presence of several degradates. Two main degradates were determined to be the cyclization product formed by photo-cyclization and the dicarboxylate formed by ring opening in the presence of base and oxygen. The identities of these degradates were confirmed by comparison of UV spectra and HPLC retention time with the independently synthesized products. The mechanistic pathways for the formation of these degradates are discussed. Further improvement of the HPLC method's ruggedness has been made based on these studies.