Xiaodong Bu

Rapid catalyst identification for the synthesis of the pyrimidinone core of HIV integrase inhibitors.

A microscale chemistry improvement engine: a pre-dosed microscale high-throughput experimentation additives platform enables rapid, serendipitous reaction improvement. This platform allowed one chemist to set up 475 experiments and analyze the results using MISER chromatography in a single day, thus resulting in two high-quality catalytic systems for the construction of the title compound 1. Support for a single-electron transfer mechanism was obtained.

A competitive and reversible deactivation approach to catalysis-based quantitative assays

Catalysis-based signal amplification makes optical assays highly sensitive and widely useful in chemical and biochemical research. However, assays must be fine-tuned to avoid signal saturation, substrate depletion and nonlinear performance. Furthermore, once stopped, such assays cannot be restarted, limiting the dynamic range to two orders of magnitude with respect to analyte concentrations. In addition, abundant analytes are difficult to quantify under catalytic conditions due to rapid signal saturation. Herein, we report an approach in which a catalytic reaction competes with a concomitant inactivation of the catalyst or consumption of a reagent required for signal generation. As such, signal generation proceeds for a limited time, then autonomously and reversibly stalls. In two catalysis-based assays, we demonstrate restarting autonomously stalled reactions, enabling accurate measurement over five orders of magnitude, including analyte levels above substrate concentration. This indicates that the dynamic range of catalysis-based assays can be significantly broadened through competitive and reversible deactivation.

Macrocyclic glycopeptide chiral selectors bonded to core-shell particles enables enantiopurity analysis of the entire verubecestat synthetic route

Verubecestat is an inhibitor of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) being evaluated in clinical trials for the treatment of Alzheimers disease. Synthetic route development involves diastereoselective transformations with a need for enantiomeric excess (ee) determination of each intermediate and final active pharmaceutical ingredient (API). The analytical technical package of validated methods relies on enantioselective SFC and RPLC separations using multiple 3 and 5 μm coated polysaccharide-based chiral stationary phases (CSPs) and mobile phases combinations. Evaluation of recently developed chiral columns revealed a single chiral selector (Teicoplanin) bonded to 2.7 μm core-shell particles using H3PO4 in H2O/ACN and triethylammonium acetate: methanol based eluents at different isocratic compositions allowed good enatioseparation of all verubecestat intermediates. EE determination of verubecestat is easily performed on NicoShell, another macrocyclic glycopeptide chiral selector bonded to 2.7 μm superficially porous particles. This approach enables fast and reliable enantiopurity analysis of the entire verubecestat synthetic route using only two chiral columns and mobile phases on a conventional HPLC system, simplifying technical package preparation, method validation and transfer to manufacturing facilities.

Evaluation of a compact mass spectrometer for routine support of pharmaceutical chemistry.

The suitability of a recently introduced inexpensive, compact mass spectrometer detector is evaluated for supporting pharmaceutical chemistry investigations. While high performance/high cost MS detectors dominate the marketplace, there is growing recognition of the need for a small, inexpensive MS detector with reduced capabilities for supporting synthetic chemistry investigations, where reduced sensitivity and unit mass resolution are often suitable for solving routine problems. In this study, the fundamental performance characteristics of the recently introduced Advion compact mass spectrometer were evaluated, investigating the use of the instrument for routine product and impurity identification, reaction monitoring, evaluation of potential genotoxic impurities and study of high molecular weight biomolecules. In general, the results of the evaluation show this compact and inexpensive mass spectrometer to be well suited for providing reliable support for pharmaceutical chemistry investigations, with sub-nanogram limit of detection and impurity identification below 0.1% being possible in some instance.

9.02 High-Throughput Analysis for High-Throughput Experimentation in Organic Chemistry

As high-throughput experimentation (HTE) emerges as an important enabling technology in the field of organic synthesis, high-throughput analysis (HTA) becomes an integral component in these newly introduced HTE platforms. Without corresponding improvements in analytical throughput, HTE platforms would quickly be limited by backlogs in chemical analysis. This review covers high-throughput developments in traditional chromatographic techniques as well as spectroscopic and mass spectrometry methods including sensor-based approaches. Both high speed and multiparallel approaches to analysis are discussed.

Isolation and analysis of trace level of silicone oil in pharmaceutical bulk drug substance by ICP-AES

In order to evaluate the extent of silicone oil contamination in a drug substance derived from processing equipment, a novel extraction method was developed which uses a mixture of polar and non-polar solvents (toluene/acetonitrile). Unlike the majority of silicone oil extraction methods in the literature that yield very low recoveries, this procedure proved able to completely recover the silicone oil from this compound. The recovered silicone oil was rediluted in isopropanol alcohol (IPA)/toluene mixture and subsequently analyzed by an inductively coupled plasma atomic emission spectrometer (ICP-AES) coupled to an ultrasonic nebulizer (USN).

GC-FID method for high-throughput analysis of residual solvents in pharmaceutical drugs and intermediates

Gas Chromatography-Flame Ionization Detection (GC-FID) analysis for quantitation of residual solvents in drugs and synthetic intermediates is one of the most important and frequently used tests in the pharmaceutical industry. However, as currently practiced, the technique requires significant sample preparation time, in addition to having a very poor ‘green factor’ (Analytical Method Volume Intensity, or AMVI). In this study, a simple and fast protocol using multi-solvent standard mixtures combined with a seven minute universal GC-FID method (using either He or H2 as carrier gas) and Empower™ data analysis is presented. We demonstrate that standard mixtures containing solvents commonly used in process chemistry workflows can be stored in crimped HPLC vials at −10 °C for at least 31 months. The 31 months stability data showed over 97% recovery for all 25 solvents, with overall relative standard deviation below 5%. Our approach simplifies tremendously the tedious task of residual solvent quantitation, resulting in significantly less labor, greater reliability, faster time to result and at least a 290 fold reduction in solvent consumption and hazardous waste disposal.

Mechanistic insight into oxidized N,N-dimethylacetamide as a source of formaldehyde related derivatives

A hemiaminal derivative identified during preparation of the penultimate of ceftolozane 1, mandated a thorough investigation of the source of the impurity. N,N-Dimethylacetamide (DMAc) subjected to oxidation was found to be the culprit generating oxidized products that serve as sources of the hemiaminal derivative. Identification of DMAc as a source of formaldehyde derivatives and the mechanism of DMAc oxidation are elaborated.

Generic gas chromatography-flame ionization detection method for quantitation of volatile amines in pharmaceutical drugs and synthetic intermediates

Volatile amines are among the most frequently used chemicals in organic and pharmaceutical chemistry. Synthetic route optimization often involves the evaluation of several different amines requiring the development and validation of analytical methods for quantitation of residual amine levels. Herein, a simple and fast generic GC-FID method on an Agilent J&W CP-Volamine capillary column (using either He or H2 as the carrier gas) capable of separating over 25 volatile amines and other basic polar species commonly used in pharmaceutical chemistry workflows is described. This 16min method is successfully applied to the analysis and quantitation of volatile amines in a variety of pharmaceutically-related drugs and synthetic intermediates. Method validation experiments showed excellent analytical performance in linearity, recovery, repeatability, and limit of quantitation and detection. In addition, diverse examples for the application of this method to the simultaneous determination of other amine-related chemicals in reaction mixtures are illustrated, thereby indicating that these GC-FID method conditions can be effectively used as starting point during method development for the analysis of other basic polar species beyond the validated list of amines described in this study.

Study of hypochlorite-specific enhancement in ICP-AES and ICP-MS

Severe chlorine signal enhancement in ICP-AES (by a factor of 2.6 to 3) and ICP-MS (by a factor of about 2) was found in the determination of Cl in hypochlorite (ClO−) but not in the determination of Cl in four other chlorine-containing species (Cl−, ClO2−, ClO3−, and ClO4−). A near linear correlation between the extent of the enhancement and the hypochlorite concentration was established, and the enhancement can only be removed by converting hypochlorite into other chlorine-containing species.