Recent Developments in Mass Spectrometry to Support Next-Generation Synthesis and Screening.

The complexity of new therapeutics continues to increase and the timeline for the discovery of these therapeutics continues to shrink. This creates demand for new analytical techniques to facilitate quicker discovery and development of novel drugs. Mass spectrometry is one of the most prolific analytical techniques that has been applied across the entire drug discovery pipeline. New mass spectrometers and the associated methods for sampling have been introduced at a rate that keeps pace with new chemistries, therapeutic types, and screening practices used by modern drug hunters. This microperspective covers application and implementation of new mass spectrometry workflows that enable current and future efforts in screening and synthesis for drug discovery.

Rearrangement of 3-Hydroxyazetidines into 2-Oxazolines.

A novel rearrangement sequence of 3-hydroxyazetidines via a Ritter initiated cascade provides highly substituted 2-oxazolines in high yields. The reaction conditions and substrate scope of the transformation have been studied demonstrating the generality of the process. The derived products can also be functionalized in order to undergo further intramolecular cyclization leading to a new class of macrocycle. The final cyclization step was shown to be a transformation amenable to continuous flow processing allowing for a dramatic reduction in the reaction time and simple scale-up.

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.

Electrochemical Aminoxyl-Mediated α-Cyanation of Secondary Piperidines for Pharmaceutical Building Block Diversification.

Secondary piperidines are ideal pharmaceutical building blocks owing to the prevalence of piperidines in commercial drugs. Here, we report an electrochemical method for cyanation of the heterocycle adjacent to nitrogen without requiring protection or substitution of the N-H bond. The reaction utilizes ABNO (9-azabicyclononane N-oxyl) as a catalytic mediator. Electrochemical oxidation of ABNO generates the corresponding oxoammonium species, which promotes dehydrogenation of the 2° piperidine to the cyclic imine, followed by addition of cyanide. The low-potential, mediated electrolysis process is compatible with a wide range of heterocyclic and oxidatively sensitive substituents on the piperidine ring and enables synthesis of unnatural amino acids.

De Novo Design, Synthesis, and Biological Evaluation of 3,4-Disubstituted Pyrrolidine Sulfonamides as Potent and Selective Glycine Transporter 1 Competitive Inhibitors.

The development of glycine transporter 1 (GlyT1) inhibitors may offer putative treatments for schizophrenia and other disorders associated with hypofunction of the glutaminergic N-methyl-d-aspartate (NMDA) receptor. Herein, we describe the synthesis and biological evaluation of a series of 3,4-disubstituted pyrrolidine sulfonamides as competitive GlyT1 inhibitors that arose from de novo scaffold design. Relationship of chemical structure to drug-drug interaction (DDI) and bioactivation was mechanistically investigated. Murine studies were strategically incorporated into the screening funnel to provide early assessments of in vivo target occupancy (TO) by ex vivo binding studies. Advanced compounds derived from iterative structure-activity relationship (SAR) studies possessed high potency in ex vivo binding studies and good brain penetration, promising preliminary in vivo efficacy, acceptable preclinical pharmacokinetics, and manageable DDI and bioactivation liabilities.

Selective C(sp3 )-H Aerobic Oxidation Enabled by Decatungstate Photocatalysis in Flow.

A mild and selective C(sp3 )-H aerobic oxidation enabled by decatungstate photocatalysis has been developed. The reaction can be significantly improved in a microflow reactor enabling the safe use of oxygen and enhanced irradiation of the reaction mixture. Our method allows for the oxidation of both activated and unactivated C-H bonds (30 examples). The ability to selectively oxidize natural scaffolds, such as (-)-ambroxide, pregnenolone acetate, (+)-sclareolide, and artemisinin, exemplifies the utility of this new method.

Are We There Yet? Applying Thermodynamic and Kinetic Profiling on Embryonic Ectoderm Development (EED) Hit-to-Lead Program.

It is advocated that kinetic and thermodynamic profiling of bioactive compounds should be incorporated and utilized as complementary tools for hit and lead optimizations in drug discovery. To assess their applications in the EED hit-to-lead optimization process, large amount of thermodynamic and kinetic data were collected and analyzed via isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR), respectively. Slower dissociation rates (koff) of the lead compounds were observed as the program progressed. Analysis of the kinetic data indicated that compound cellular activity correlated with both Ki and koff. Our analysis revealed that ITC data should be interpreted in the context of chiral purity of the compounds. The thermodynamic signatures of the EED aminopyrrolidine compounds were found to be mainly enthalpy driven with improved enthalpic contributions as the program progressed. Our study also demonstrated that significant challenges still exist in utilizing kinetic and thermodynamic parameters for hit selection.

Pd-PEPPSI-IPent-SiO2 : A Supported Catalyst for Challenging Negishi Coupling Reactions in Flow.

A silica-supported precatalyst, Pd-PEPPSI-IPent-SiO2 , has been prepared and evaluated for its proficiency in the Negishi cross-coupling of hindered and electronically deactivated coupling partners. The precatalyst Pd-PEPPSI-IPent loaded onto packed bed columns shows high catalytic activity for the room-temperature coupling of deactivated/hindered biaryl partners. Also for the first time, the flowed Csp3 -Csp2 coupling of secondary alkylzinc reagents to (hetero)aromatics has been achieved with high selectivity with Pd-PEPPSI-IPent-SiO2 . These couplings required residence times as short as 3 minutes to effect completion of these challenging transformations with excellent selectivity for the nonrearranged product.

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.

Synthesis of Fused Pyrimidinone and Quinolone Derivatives in an Automated High-Temperature and High-Pressure Flow Reactor.

Fused pyrimidinone and quinolone derivatives that are of potential interest to pharmaceutical research were synthesized within minutes in up to 96% yield in an automated Phoenix high-temperature and high-pressure continuous flow reactor. Heterocyclic scaffolds that are either hard to synthesize or require multisteps are readily accessible using a common set of reaction conditions. The use of low-boiling solvents along with the high conversions of these reactions allowed for facile workup and isolation. The methods reported herein are highly amenable for fast and efficient heterocycle synthesis as well as compound scale-ups.

Current status and future prospects for enabling chemistry technology in the drug discovery process.

This review covers recent advances in the implementation of enabling chemistry technologies into the drug discovery process. Areas covered include parallel synthesis chemistry, high-throughput experimentation, automated synthesis and purification methods, flow chemistry methodology including photochemistry, electrochemistry, and the handling of "dangerous" reagents. Also featured are advances in the "computer-assisted drug design" area and the expanding application of novel mass spectrometry-based techniques to a wide range of drug discovery activities.

Automated library synthesis of cyclopropyl boronic esters employing diazomethane in a tube-in-tube flow reactor.

The efficient synthesis of cyclopropyl boronic esters in library format using a diazomethane flow reactor has been achieved. A pivotal component of the system is a fully automated tube-in-tube reactor allowing for safe handling of hazardous diazomethane on repeated small scale and for the generation of larger quantities of product. The setup enables the repeated execution of Pd-catalyzed cyclopropanation reactions without compromising its operation over time.

High-Temperature Boc Deprotection in Flow and Its Application in Multistep Reaction Sequences.

A simplified Boc deprotection using a high-temperature flow reactor is described. The system afforded the qualitative yield of a wide variety of deprotected substrates within minutes using acetonitrile as the solvent and without the use of acidic conditions or additional workups. Highly efficient, multistep reaction sequences in flow are also demonstrated wherein no extraction or isolation was required between steps.