High performance liquid chromatographic enantioseparation development and analytical method characterization of the carboxylate ester of evacetrapib using an immobilized chiral stationary phase with a non-conventional eluent system.

Using multiple HPLC chromatographic modes and various chiral columns in the context of an automated screening system, a potential separation was initially identified for the methyl ester of evacetrapib and its stereoisomers using an immobilized polysaccharide-based HPLC column. The bonded nature of this column, the Chiralpak(®) IC, allows for enhanced separation development with a diverse solvent range not amenable to standard coated chiral stationary phases. The ternary eluent system ultimately identified provided isomer resolutions not obtainable via the more established hexane/alcohol or polar organic chromatographic modes. A systematic separation development process is described, first for the resolution of the isomers, and later incorporating five potential impurities. A robust separation system was eventually developed that effectively resolves all compounds within a reasonable analysis time.

Metabolism of LY654322, a growth hormone secretagogue, to an unusual diimidazopyridine metabolite.

2-Methylalanyl-N-{1-[(1R)-1-(4-fluorophenyl)-1-methyl-2-oxo-2-pyrrolidin-1-ylethyl]-1H-imidazol-4-yl}-5-phenyl-D-norvalinamide (LY654322) was rapidly cleared in rats and dogs by renal excretion of parent and metabolism (oxidative and hydrolytic). Among the metabolites identified in the urine of rats and dogs was M25, which was structurally unusual. Indeed, the characterization of M25 and investigation into its disposition relied on the convergence of diverse analytical methodologies. M25 eluted after the parent on reverse-phase chromatography with an MH(+) at m/z 598 (parent + 35 Da). Given its increased lipophilicity and its mass difference compared with the parent, it was evident that M25 was not a phase 2 conjugate. Subsequent liquid chromatography with multiple-stage tandem mass spectrometry and accurate mass experiments identified the structure of M25 as having two replicates of the 1-(4-fluorophenyl)-1-methyl-2-oxo-2-pyrrolidinyl substructure flanking a central aromatic core of composition C(7)H(3)N(5) that was refractory to fragmentation. Compared with the UV spectrum of the parent (λ(max) = 213 nm), M25 displayed a bathochromic shift (λ(max) = 311 nm), which substantiated extensive conjugation within the central core. Subsequent NMR analysis of M25 isolated from dog urine coupled with molecular modeling revealed the structure to be consistent with a diimidazopyridine core with two symmetrically substituted 1-(4-fluorophenyl)-1-methyl-2-oxo-2-pyrrolidinyl moieties. Using a structural analog with a chromophore similar to M25, LC-UV was used to quantitate M25 and determine its urinary disposition. The formation of M25 appears consistent with hydrolysis of LY654322 to an aminoimidazole, dimerization of the latter with the loss of NH(3), C-formylation, and subsequent ring closure and aromatization with loss of H(2)O.

Selective reduction of N-oxides to amines: application to drug metabolism.

Phase I oxidative metabolism of nitrogen-containing drug molecules to their corresponding N-oxides is a common occurrence. There are instances where liquid chromatography/tandem mass spectometry techniques are inadequate to distinguish this pathway from other oxidation processes, including C-hydroxylations and other heteroatom oxidations, such as sulfur to sulfoxide. Therefore, the purpose of the present study was to develop and optimize an efficient and practical chemical method to selectively convert N-oxides to their corresponding amines suitable for drug metabolism applications. Our results indicated that efficient conversion of N-oxides to amines could be achieved with TiCl(3) and poly(methylhydrosiloxane). Among them, we found TiCl(3) to be a facile and easy-to-use reagent, specifically applicable to drug metabolism. There are a few reports describing the use of TiCl(3) to reduce N-O bonds in drug metabolism studies, but this methodology has not been widely used. Our results indicated that TiCl(3) is nearly as efficient when the reductions were carried out in the presence of biological matrices, including plasma and urine. Finally, we have shown a number of examples where TiCl(3) can be successfully used to selectively reduce N-oxides in the presence of sulfoxides and other labile groups.