Biomedical subjects

Yingru Zhang

Publications and source records attributed to Yingru Zhang.

6 recordsLinked to original sources

PubMed2006

NMR characterization of an S-linked glucuronide metabolite of the potent, novel, nonsteroidal progesterone agonist tanaproget.

Tanaproget is a first-in-class nonsteroidal progesterone receptor agonist that is being investigated for use in contraception. A major in vitro and in vivo metabolite of tanaproget formed in humans was initially characterized as a glucuronide of tanaproget. However, whether the glucuronide was linked to the nitrogen or sulfur of the benzoxazine-2-thione group in tanaproget could not be determined by liquid chromatography/mass spectrometry (LC/MS) and LC-tandem mass spectrometry analysis. To obtain additional structural details for this metabolite, additional quantities were generated from rat liver microsomal incubations and purified by high-performance liquid chromatography (HPLC) for NMR analysis. The NMR data for the metabolite confirmed that the glucuronide was covalently bound to either the sulfur or the nitrogen of the benzoxazine-2-thione moiety. The lack of key through-bond (scalar) and through-space (dipolar) one-dimensional (1D) and two-dimensional (2D) NMR couplings and correlations in the metabolite spectra (due primarily to low sample concentration) precluded an unambiguous structure elucidation. Subsequent synthesis of the S- and N-glucuronides of tanaproget from tanaproget facilitated the unambiguous regio- and stereochemical assignment of the metabolite by comparison of 1D NMR chemical shifts and scalar coupling constants, 2D NMR correlations, and HPLC and LC/MS characteristics between the synthetic compounds and the metabolite. From extensive comparison of the spectral and chromatographic data of the microsomally derived metabolite and the synthetic compounds, the metabolite has been determined to be the S-(beta)-D-glucuronide of tanaproget.

Animals↗

PubMed2005

Preparative separation and identification of derivatized beta-methylphenylalanine enantiomers by chiral SFC, HPLC and NMR for development of new peptide ligand mimetics in drug discovery.

A direct preparative purification of all four isomers of the unnatural amino acid beta-methylphenylalanine was achieved using supercritical fluid chromatography (SFC) with stacked-injection. Final purification of the Cbz-methyl ester derived isomers was performed on a Daicel Chiralpak AD-H column (20 mm x 250 mm), using 50:50 methanol/ethanol as the organic modifier and resulted in purification of over 3.4 g of material in 6.25 h with >90% total recovery. The absolute stereochemical assignment of the purified amino acids was determined through a combination of chiral HPLC, NMR and optical rotation studies. To our knowledge, this is the first reported preparative approach that has yielded all four compounds in a single chromatographic run.

Aminobutyrates↗

PubMed2005

Absolute configuration of C2-symmetric spiroselenurane: 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole.

The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound.

Journal Article↗

PubMed2005

Enantioselective chromatography in drug discovery.

Molecular chirality is a fundamental consideration in drug discovery, one necessary to understand and describe biological targets as well as to design effective pharmaceutical agents. Enantioselective chromatography has played an increasing role not only as an analytical tool for chiral analyses, but also as a preparative technique to obtain pure enantiomers from racemates quickly from a wide diversity of chemical structures. Different enantioselective chromatography techniques are reviewed here, with particular emphasis on the most widespread high performance liquid chromatography (HPLC) and the rapidly emerging supercritical fluid chromatography (SFC) techniques. This review focuses on the dramatic advances in the chiral stationary phases (CSPs) that have made HPLC and SFC indispensable techniques for drug discovery today. In addition, screening strategies for rapid method development and considerations for laboratory-scale preparative separation are discussed and recent achievements are highlighted.

Amylose↗

PubMed2004

Rapid method development for chiral separation in drug discovery using multi-column parallel screening and circular dichroism signal pooling.

A novel strategy for rapid chiral method development has been developed using multi-column parallel screening and circular dichroism (CD) signal pooling. Described is the first use of a customized HPLC system that integrates an HPLC auto-sampler, one pump and five divided channels with five columns and five UV detectors to screen five chiral stationary phases (CSPs) simultaneously in parallel. A high-pressure semi-prep on-line pre-filter, a six-port manifold and five individually adjusted backpressure restrictors were installed in the system which allowed the sample and mobile phase to be evenly distributed over the five columns and UV detectors. The five CSPs, namely Chiralpak AD and AS, Chiralcel OJ and OD and Whelk-O1, were screened. The system guarantees a five-fold increase in speed for chiral column scouting compared with the widely used automated sequential column switching approach, and does not have the limitations of the coupled column screening approach for enantiomers whose elution order could be reversed on CSPs. Furthermore, the five channels after the UV detectors were recombined using a reversed flow splitter into a CD detector. The pooled CD signal from the five channels was recorded to track the elution order of the resolved enantiomers and to determine their sign, positive or negative. The signal pooling allows for the effective use of a single CD detector for multiple columns since unresolved racemate has little CD signal, and observing the sign of CD signal for one of the two enantiomer UV peaks is sufficient for tracking the enantiomeric elution order.

Chromatography, High Pressure Liquid↗

PubMed2004

Simulated moving columns technique for chiral liquid chromatography.

Enantioselectivity of chiral selectors is often relatively low in chiral HPLC. For difficult chiral separations, often only partial resolution is obtained rather quickly by column and mobile phase screening, and, by trial-and-error, additional method optimization is required to achieve complete resolution. This paper describes the development of a novel column-switching technique called "simulated moving columns" (SMC) to quickly achieve complete chiral resolution on columns with limited enantioselectivity. The simulated moving columns (SMC) technique uses two (2) or three (3) short chiral HPLC columns connected in series, and forces the unresolved enantiomers to recycle exclusively through the columns until sufficient resolution is attained. In effect, SMC helps to achieve chiral resolution by virtually multiplying the column length, thus enhancing separation efficiency and resolution, without increasing backpressure. Comparison of the standard non-SMC approach with SMC, and selected applications of chiral separations of pharmaceutical drug molecules are presented. Through measurement and calculation, evaluation of off-column band broadening resulting from a two-column SMC system is provided. The results clearly indicate that SMC eliminates the significant band broadening that is inevitable in the closed-loop recycling techniques currently used in preparative chromatography. Furthermore, SMC is not only useful to enhance resolution for analytical and preparative chiral separation, but also has great potential to enhance recovery and purity for difficult chiral preparative chromatography.

Algorithms↗