Biomedical subjects

Oliver McConnell

Publications and source records attributed to Oliver McConnell.

9 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

Enhanced chromatographic resolution of amine enantiomers as carbobenzyloxy derivatives in high-performance liquid chromatography and supercritical fluid chromatography.

The carbobenzyloxy (cbz) protecting group is evaluated for it's potential to enhance the resolution of chiral amine enantiomers using high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). A series of cbz derivatives of commercially available racemates was prepared and analyzed by enantioselective chromatography using a variety of mobile phases and polysaccharide and Pirkle-type chiral stationary phases (CSPs). The cbz-derivatized product consistently demonstrated enhanced chiral resolution under HPLC and SFC conditions. Improved selectivity and resolution combined with an automated preparative HPLC or SFC system can lead to the rapid generation of highly purified enantiomers of desirable starting materials, intermediates or final products.

Amines↗

PubMed2005

Advantages of atmospheric pressure photoionization mass spectrometry in support of drug discovery.

The performance of the atmospheric pressure photoionization (APPI) technique was evaluated against five sets of standards and drug-like compounds and compared to atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The APPI technique was first used to analyze a set of 86 drug standards with diverse structures and polarities with a 100% detection rate. More detailed studies were then performed for another three sets of both drug standards and proprietary drug candidates. All 60 test compounds in these three sets were detected by APPI with an overall higher ionization efficiency than either APCI or ESI. Most of the non-polar compounds in these three sets were not ionized by APCI or ESI. Analysis of a final set of 201 Wyeth proprietary drug candidates by APPI, APCI and ESI provided an additional comparison of the ionization techniques. The detection rates in positive ion mode were 94% for APPI, 84% for APCI, and 84% for ESI. Combining positive and negative ion mode detection, APPI detected 98% of the compounds, while APCI and ESI detected 91%, respectively. This analysis shows that APPI is a valuable tool for day-to-day usage in a pharmaceutical company setting because it is able to successfully ionize more compounds, with greater structural diversity, than the other two ionization techniques. Consequently, APPI could be considered a more universal ionization method, and therefore has great potential in high-throughput drug discovery especially for open access liquid chromatography/mass spectrometry (LC/MS) applications.

Animals↗

PubMed2005

Integrity profiling of high throughput screening hits using LC-MS and related techniques.

Integrity profiling of HTS hits is valuable for verification of the hit identity and purity. This provides early discovery researchers with more confident SAR theories. Methodology for integrity profiling of HTS hits must be high throughput, consume little material, and selectively provide structure-based data. Analytical techniques that can be utilized for integrity profiling methods are reviewed for their appropriateness in sample preparation, component separation, detection, purity quantitation, identity confirmation, and follow-up.

Chromatography, Liquid↗

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↗

PubMed2004

Brain and plasma exposure profiling in early drug discovery using cassette administration and fast liquid chromatography-tandem mass spectrometry.

A method using reverse phase liquid chromatography-tandem mass spectrometry and cassette administration was developed for in vivo brain and plasma exposure profiling to assist early CNS drug discovery programs. Three to four compounds were grouped in cassettes for dosing and analysis. Compounds in the cassettes were selected to minimize possible analytical interference from each other, as well as from their potential metabolites. In order to improve the confidence of cassette administration, an analogue of the study compounds, with well-established brain penetration data, was included in each cassette as a "biological internal standard". Compounds were administered to rats by intraperitoneal injection and extracted from plasma or brain homogenate by simple protein precipitation. Fast chromatographic separation was achieved by using a short narrow-bore column at a flow rate of 1.0ml/min with a fast gradient. The brain penetration of the compounds was evaluated by comparing their C(max) and AUC values in brain and plasma. This approach rapidly provided early brain penetration and plasma exposure information, thus making more of this data available to teams. Comparing the brain exposures to the EC(50) values (i.e. in vitro potency) of series compounds in the same discovery program provided another dimension of information to select lead compounds for future in vivo assessment. The method described here has been used for providing early brain penetration information in several CNS exploratory and discovery programs.

Animals↗

PubMed2003

Pharmaceutical profiling method for lipophilicity and integrity using liquid chromatography-mass spectrometry.

A method is described for the simultaneous profiling of sample lipophilicity, integrity, and purity. The method is rapid and is applicable to high throughput profiling of pharmaceutical properties in drug discovery. A short Polaris C(18) column is used with a rapid, wide-polarity mobile phase gradient, UV detection, and MS analysis. The lipophilicity of each component is estimated from a calibration curve using six drug or organic compounds and plotting their respective measured retention time versus LogD(7.4) (literature). The correlation of LogD(7.4) (literature) to LogD(7.4) (HPLC) for 60 structurally diverse drugs has a correlation coefficient r(2) of 0.89. The method is applicable to compounds with MW>200 and retention time>1.5 min for rapid, initial pharmaceutical profiling in drug discovery.

Chromatography, High Pressure Liquid↗

PubMed2003

Relative hydrophobicity and lipophilicity of drugs measured by aqueous two-phase partitioning, octanol-buffer partitioning and HPLC. A simple model for predicting blood-brain distribution.

Relative hydrophobicity and lipophilicity of 63 compounds with known permeability through the blood-brain barrier (BBB) was examined by partitioning in aqueous dextran-poly(ethylene glycol) two-phase system and octanol-buffer system, and by gradient RP-HPLC at pH 7.4. Combination of the relative hydrophobicity estimates, N(CH(2)) obtained by aqueous two-phase partitioning and the lipophilicity (logD(exp) or logD(HPLC)) values obtained by the shake-flask technique or HPLC technique allows one to differentiate between compounds capable of crossing the BBB and those that cannot. A simple model for predicting blood-brain distribution is proposed.

Blood-Brain Barrier↗