Xiaoyi Gong

Systematic evaluation of new chiral stationary phases for supercritical fluid chromatography using a standard racemate library.

A systematic approach to the evaluation of new chiral stationary phases (CSPs) for supercritical fluid chromatography (SFC) using a standard library of racemic analytes is described. A standard library of racemic analytes representing a variety of functional group classes was assembled from a mixture of proprietary and commercial compounds. The library is dispensed and stored in a convenient 96-well microplate format to facilitate ease of use, and to minimize the amount of analyte required for analysis. Automated SFC screening was performed on both established CSPs in common use, as well as a group of six recently commercialized CSPs. Screening results were archived in a structure-searchable database that allows convenient comparison of performance data to determine which CSPs shows the best performance.

Performance to burn? Re-evaluating the choice of acetonitrile as the platform solvent for analytical HPLC

Acetonitrile is by far the preferred organic solvent for use in Reversed Phase High Performance Liquid Chromatography (RP-HPLC) today, owing to an excellent combination of physical properties of this solvent that are favorable for chromatography (viscosity, UV absorbance cutoff, boiling point). In recent years, improvements in both instrument and stationary phase technologies have greatly enhanced the performance of routine laboratory HPLC, leading to an excess of performance for many users. In this study we re-examine the choice of acetonitrile as the platform organic solvent for HPLC, addressing the question of whether greener solvents such as ethanol could potentially replace acetonitrile in some instances.

Improved chiral SFC screening for analytical method development.

In this study we describe the evaluation of a recently developed supercritical fluid chromatography (SFC) instrument for automated chiral SFC method development. The greatly improved gradient dwell volume and liquid flow control of the new instrument in combination with the use of shorter columns containing smaller stationary phase particles affords chiral SFC method development that is faster and more universal than previous systems.

Supercritical fluid chromatography for GMP analysis in support of pharmaceutical development and manufacturing activities.

Supercritical fluid chromatography (SFC) has long been a preferred method for enantiopurity analysis in support of pharmaceutical discovery and development, but implementation of the technique in regulated GMP laboratories has been somewhat slow, owing to limitations in instrument sensitivity, reproducibility, accuracy and robustness. In recent years, commercialization of next generation analytical SFC instrumentation has addressed previous shortcomings, making the technique better suited for GMP analysis. In this study we investigate the use of modern SFC for enantiopurity analysis of several pharmaceutical intermediates and compare the results with the conventional HPLC approaches historically used for analysis in a GMP setting. The findings clearly illustrate that modern SFC now exhibits improved precision, reproducibility, accuracy and robustness; also providing superior resolution and peak capacity compared to HPLC. Based on these findings, the use of modern chiral SFC is recommended for GMP studies of stereochemistry in pharmaceutical development and manufacturing.

Development of LC chiral methods for neutral pharmaceutical related compounds using reversed phase and normal phase liquid chromatography with different types of polysaccharide stationary phases

The enantioselectivity of a collection of neutral pharmaceutical compounds on six different types of polysaccharide chiral stationary phases (CSPs), Chiralpak AD (and AD-RH), Chiralcel OD (and OD-RH), Chiralpak OJ (and OJ-R), Chiralcel AS (and AS-RH), Sepapak-2 and Sepapak-4 are compared using reversed phase (RPLC) and normal phase liquid chromatography (NPLC). Screening strategies for maximizing the probability of achieving an initial chiral separation hit for neutral compounds using both RPLC and NPLC are described. Further method optimizations are demonstrated by modifying parameters such as organic modifier composition, eluent pH or CSP particle size. Several practical examples of the application of chiral methods for the study of synthetic reaction mixtures are presented. The most critical validation aspects, including limit of detection, specificity, and ruggedness, are also briefly presented.

Systematic approach to conformational sampling for assigning absolute configuration using vibrational circular dichroism.

Systematic methods that speed-up the assignment of absolute configuration using vibrational circular dichrosim (VCD) and simplify its usage will advance this technique into a robust platform technology. Applying VCD to pharmaceutically relevant compounds has been handled in an ad hoc fashion, relying on fragment analysis and technical shortcuts to reduce the computational time required. We leverage a large computational infrastructure to provide adequate conformational exploration which enables an accurate assignment of absolute configuration. We describe a systematic approach for rapid calculation of VCD/IR spectra and comparison with corresponding measured spectra and apply this approach to assign the correct stereochemistry of nine test cases. We suggest moving away from the fragment approach when making VCD assignments. In addition to enabling faster and more reliable VCD assignments of absolute configuration, the ability to rapidly explore conformational space and sample conformations of complex molecules will have applicability in other areas of drug discovery.

Analysis of volatile bases by high performance liquid chromatography with aerosol-based detection

The development and performance of two methods are described whereby low levels of volatile bases are quantified by HPLC using either a charged aerosol detector (CAD) or a nano-quantity analyte detector (NQAD). A test set of 12 volatile bases (ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, isobutylamine, N,N-diisopropylethylamine, morpholine, piperazine, ethylenediamine, and 1,4-diazabicyclo[2.2.2]octane) were analyzed. The studied compounds all exhibit poor UV chromophores and are typically undetectable by aerosol-based detection when using conventional volatile mobile phases. The ability to detect these analytes by CAD or NQAD depended on their propensity towards formation of a low volatility salt between the target analyte and mobile phase modifier. Trifluoroacetic acid (TFA) was found to significantly improve detection of most volatile bases. A low concentration (0.2 mM) of hydrochloric acid was additionally needed to enable detection of ammonia. The compounds were separated under hydrophilic interaction liquid chromatography (HILIC) conditions on a zic-pHILIC column. For all analytes, limits of detection (LOD) were measured in the range of 1-27 ng on column, which is comparable to previously reported detection limits for non-volatile analytes.

Microscale HPLC enables a new paradigm for commercialization of complex chiral stationary phases

The small column size (0.3 mm i.d. x 15 cm) used in microscale HPLC contains only a small fraction (<1%) of the chromatographic packing material of a typical analytical HPLC column. Consequently, chromatographic stationary phases that are prohibitively expensive in conventional HPLC, owing either to synthetic complexity or costly starting materials, may become commercially viable in the microscale format. To illustrate this point, a previously described, synthetically complex, crown ether chiral stationary phase was prepared and evaluated in the microscale format, showing excellent separation of the enantiomers of underivatized amine analytes.

Discovery of Benzodiazepine Sulfonamide-Based Bombesin Receptor Subtype 3 Agonists and Their Unusual Chirality

We report herein the discovery of benzodiazepine sulfonamide-based bombesin receptor subtype 3 (BRS-3) agonists and their unusual chirality. Starting from a high-throughput screening lead, we prepared a series of BRS-3 agonists with improved potency and pharmacokinetic properties, of which compound 8a caused mechanism-based, dose-dependent food intake reduction and body weight loss after oral dosing in diet-induced obese mice. This effort also led to the discovery of a novel family of chiral molecules originated from the conformationally constrained seven-membered diazepine ring.

The design and synthesis of potent, selective benzodiazepine sulfonamide bombesin receptor subtype 3 (BRS-3) agonists with an increased barrier of atropisomerization.

Bombesin receptor subtype 3 (BRS-3) is an orphan G-protein coupled receptor expressed primarily in the hypothalamus which plays a role in the onset of both diabetes and obesity. We report herein our progress made towards identifying a potent, selective bombesin receptor subtype-3 (BRS-3) agonist related to the previously described MK-7725(1) Chobanian et al. (2012) that would prevent atropisomerization through the increase of steric bulk at the C-2 position. This would thereby make clinical development of this class of compounds more cost effective by inhibiting racemization which can occur over long periods of time at room/elevated temperature.