Solvent Effects on the Chemo- and Site-Selectivity of Transition Metal-Catalyzed Nitrene Transfer Reactions: Alternatives to Chlorinated Solvents.

Transition metal-catalyzed, non-enzymatic nitrene transfer (NT) reactions to selectively transform C-H and C=C bonds to new C-N bonds are a powerful strategy to streamline the preparation of valuable amine building blocks. However, many catalysts for these reactions use environmentally unfriendly solvents that include dichloromethane, chloroform, 1,2-dichloroethane and benzene. We developed a high-throughput experimentation (HTE) protocol for heterogeneous NT reaction mixtures to enable rapid screening of a broad range of solvents for this chemistry. Coupled with the American Chemical Society Pharmaceutical Roundtable (ACSPR) solvent tool, we identified several attractive replacements for chlorinated solvents. Selected catalysts for NT were compared and contrasted using our HTE protocol, including silver supported by N-dentate ligands, dinuclear Rh complexes and Fe/Mn phthalocyanine catalysts.

Readily Accessible High-Throughput Experimentation: A General Protocol for the Preparation of ChemBeads and EnzyBeads.

Chemical- and enzyme-coated beads (ChemBeads and EnzyBeads) were introduced recently as a universal strategy for the accurate dispensing of various solids in submilligram quantities using automated instrumentation or manual dispensing. The coated beads are prepared using a resonant acoustic mixer (RAM)-an instrument that may be available only to well-established facilities. In this study, we evaluated alternative coating methods for preparing ChemBeads and EnzyBeads without the use of a RAM. We also evaluated the effects of bead sizes on loading accuracy using 4 coating methods and 12 solids (9 chemicals and 3 enzymes) as test subjects. While our original RAM coating method is the most versatile for the broadest range of solids, high-quality ChemBeads and EnzyBeads that are suitable for high-throughput experimentation can be prepared using alternative methods. These results should make ChemBeads and EnzyBeads readily accessible as the core technology for setting up high-throughput experimentation platforms.

ChemBeads-Enabled Photoredox High-Throughput Experimentation Platform to Improve C(sp2)-C(sp3) Decarboxylative Couplings.

Enthusiasm surrounding nickel/photoredox C(sp2)-C(sp3) cross-couplings is very high; however, these methods are sometimes challenged by complex drug-like substrates in discovery chemistry. In our hands this has been especially true of the decarboxylative coupling, which has lagged behind other photoredox couplings in internal adoption and success. Herein, the development of a photoredox high-throughput experimentation platform to optimize challenging C(sp2)-C(sp3) decarboxylative couplings is described. Chemical-coated glass beads (ChemBeads) and a novel parallel bead dispenser are used to expedite the high-throughput experimentation process and identify improved coupling conditions. In this report, photoredox high-throughput experimentation is utilized to dramatically improve low-yielding decarboxylative C(sp2)-C(sp3) couplings, and libraries, using conditions not previously identified in the literature.

High-Throughput Reaction Screening with Nanomoles of Solid Reagents Coated on Glass Beads.

Technologies that enable rapid screening of diverse reaction conditions are of critical importance to methodology development and reaction optimization, especially when molecules of high complexity and scarcity are involved. The lack of a general solid dispensing method for chemical reagents on micro- and nanomole scale prevents the full utilization of reaction screening technologies. We herein report the development of a technology in which glass beads coated with solid chemical reagents (ChemBeads) enable the delivery of nanomole quantities of solid chemical reagents efficiently. By exploring the concept of preferred screening sets, the flexibility and generality of this technology for high-throughput reaction screening was validated.

Integrated Platform for Expedited Synthesis-Purification-Testing of Small Molecule Libraries.

The productivity of medicinal chemistry programs can be significantly increased through the introduction of automation, leading to shortened discovery cycle times. Herein, we describe a platform that consolidates synthesis, purification, quantitation, dissolution, and testing of small molecule libraries. The system was validated through the synthesis and testing of two libraries of binders of polycomb protein EED, and excellent correlation of obtained data with results generated through conventional approaches was observed. The fully automated and integrated platform enables batch-supported compound synthesis based on a broad array of chemical transformations with testing in a variety of biochemical assay formats. A library turnaround time of between 24 and 36 h was achieved, and notably, each library synthesis produces sufficient amounts of compounds for further evaluation in secondary assays thereby contributing significantly to the shortening of medicinal chemistry discovery cycles.

An Automated Microwave-Assisted Synthesis Purification System for Rapid Generation of Compound Libraries.

A novel methodology for the synthesis and purification of drug-like compound libraries has been developed through the use of a microwave reactor with an integrated high-performance liquid chromatography-mass spectrometry (HPLC-MS) system. The strategy uses a fully automated synthesizer with a microwave as energy source and robotic components for weighing and dispensing of solid reagents, handling liquid reagents, capper/crimper of microwave reaction tube assemblies, and transportation. Crude reaction products were filtered through solid-phase extraction cartridges and injected directly onto a reverse-phase chromatography column via an injection valve. For multistep synthesis, crude products were passed through scavenger resins and reintroduced for subsequent reactions. All synthetic and purification steps were conducted under full automation with no handling or isolation of intermediates, to afford the desired purified products. This approach opens the way to highly efficient generation of drug-like compounds as part of a lead discovery strategy or within a lead optimization program.

An automated synthesis-purification-sample-management platform for the accelerated generation of pharmaceutical candidates.

A flexible and integrated flow-chemistry-synthesis-purification compound-generation and sample-management platform has been developed to accelerate the production of small-molecule organic-compound drug candidates in pharmaceutical research. Central to the integrated system is a Mitsubishi robot, which hands off samples throughout the process to the next station, including synthesis and purification, sample dispensing for purity and quantification analysis, dry-down, and aliquot generation.

Ultrasound-assisted click chemistry in continuous flow.

We present a study on ultrasound-promoted click chemistry reactions in a meso-flow reactor synthesis system with a copper reactor and a custom sonication piezoelectric transducer. Copper catalyzed Huisgen 1,3-dipolar cycloadditions were studied in flow with this system. Our results demonstrate that 1,4-disubstituted 1,2,3-triazole products can be generated at low temperatures and with short reaction time in good yield, due to the rate enhancement effect of sonication.

Purification of high-throughput organic synthesis libraries by counter-current chromatography.

Experiments were performed to evaluate whether counter-current chromatography (CCC) could function as an alternative purification method to reversed-phase high-performance liquid chromatography (RP-HPLC) and normal-phase supercritical fluid chromatography (SFC). RP-HPLC and SFC are the routine methods currently used in our high-throughput purification (HTP) facility for the purification of high-throughput organic synthesis (HTOS) libraries and medicinal chemistry reaction mixtures. Pre-equilibration of the solvent mixture layers was not mandatory for effective chromatography when hexanes-ethyl acetate-methanol-water (HEMW) solvent mixtures were used. Key to the use of CCC for high-throughput applications is the ability to effectively select a solvent system appropriate to each library member. Pilot-scale CCC elution time was used to estimate a starting solvent ratio and RP-HPLC retention time was then used to adjust solvent ratios within a particular library. It was also found that dimethyl sulfoxide (DMSO) and DMSO-methanol were suitable as sample injection solvents when using the HEMW solvent systems.