Quantitation of five nevirapine oxidative metabolites in human plasma using liquid chromatography-tandem mass spectrometry.

A multiple-reaction-monitoring LC/MS/MS method for the analysis of nevirapine oxidative metabolites, 2-hydroxynevirapine, 3-hydroxynevirapine, 8-hydroxynevirapine, 12-hydroxynevirapine, and 4-carboxynevirapine, in human plasma was developed and validated. The metabolites were isolated from 50 microL heparinized plasma by enzymatic hydrolysis of the glucuronide conjugates to the free metabolite followed by protein precipitation with acetonitrile. Peaks were quantitated at 3.03 min for the 4-carboxynevirapine metabolite, at 3.72, 4.27, 5.27, and 5.73 min for the positional 2-hydroxynevirapine, 12-hydroxynevirapine, 3-hydroxynevirapine, and 8-hydroxynevirapine metabolites, respectively, and 2.30 min for the internal standard, pirenzepine. The assay was accurate and precise based on assay validation controls over the nominal range of 0.010-1.0 mg/L. The average accuracy at the lowest concentration quality control (QC) sample was 16% (difference from theoretical value) for 8-hydroxynevirapine, all others were closer to their known respective standards. Within- and between-day precisions were within 12% for quality control samples for all five metabolites. Repetitive thawing and freezing did not have an effect on any metabolite through a minimum of three cycles. Thawed samples, remaining in plasma for 4 h before extraction, were within 5% of theoretical value. Stability of the extracted samples on the autosampler at room temperature was evaluated for 48 h and was observed to be within 12% of a fresh analytical sample for 2-hydroxynevirapine and 3-hydroxynevirapine; other metabolites were within 6% of theoretical value. The utility of the analytical method was demonstrated using trough steady-state plasma samples collected from 48 patients in a hepatic impairment study.

A scalable and regioselective synthesis of 2-difluoromethyl pyridines from commodity chemicals.

A scalable de novo synthesis of difluoromethyl pyridines from inexpensive materials is reported. The pyridyl subunit is built around the difluoromethyl group rather than a late stage introduction of this moiety. This user-friendly approach allows access to a diverse range of substitution patterns on all positions on the ring system and on the difluoromethyl group.

Probing the cation binding modes of macrocyclic HCV protease inhibitor BILN 2061 by multinuclear NMR.

The ability of the macrocyclic HCV protease inhibitor BILN 2061 to bind different classes of cations has been studied by (15)N, (13)C, and (1)H NMR. (15)N NMR experiments were performed at natural abundance or with isotopically labeled materials. Three classes of cations: alkali metals, alkaline earth metals, and transition metals, were examined, using two members of each class. The behavior of each cation class was found to be different, and provided insight into how metal ions interact with the molecular scaffold. These specific interactions were uncovered by examining coordination shifts, NOE correlations, and line broadening across all three nuclei.

Electronic control of chiral quaternary center creation in the intramolecular asymmetric heck reaction.

The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems.