Microscale Purification with Direct Charged Aerosol Detector Quantitation Using Selective Online One- or Two-Dimensional Liquid Chromatography.

The pharmaceutical industry is increasingly faced with challenging separations of complex crude reaction mixtures at the microscale that require the adoption of new platforms for rapid target isolation, impurity determination, and quantitation. In this study, we describe an online microscale one- or two-dimensional liquid chromatography (1D/2D-LC) system with heart-cutting and multi (triple) detector triggering in either dimension to address this need. The advantages of charged aerosol detection (CAD) are discussed for the direct quantitation of limited quantity samples, without utilizing a second analytical instrument or gradient compensation pump. In addition to the significant time and cost savings, there is no minimum recovery requirement that exists when compared to gravimetric methods for accurate microscale quantitation. This platform has been successfully used to purify 0.5-5.0 mg scale reactions in 96- or 384-well reaction plates with a gradient time of 4 min per sample. Separations performed in both dimensions are complete in less than 12 min, including trapping and column equilibration time. The isolated arrays of small-quantity investigational compounds at a high purity enable rapid exploration of chemical reaction parameters and synthetic route scouting for biological target validation.

Synthesis of HDAC Inhibitor Libraries via Microscale Workflow.

An integrated workflow has been established that enables the synthesis, purification, and subsequent biological testing of compound libraries on a microgram scale. This approach utilizes mass directed preparative HPLC in conjunction with charged aerosol detection (CAD) to generate solutions of investigational compounds at high purity and standardized concentrations, facilitating high fidelity biological testing. This new workflow successfully delivered libraries of histone deacetylase (HDAC) inhibitors that afforded biological data consistent with that obtained from standard scale parallel medicinal chemistry techniques. The advantages of this new approach to library synthesis include greatly reduced material requirements and amenability to high-throughput experimentation.

Site-Selective Synthesis of Insulin Azides and Bioconjugates.

A synthetic method to access novel azido-insulin analogs directly from recombinant human insulin (RHI) was developed via diazo-transfer chemistry using imidazole-1-sulfonyl azide. Systematic optimization of reaction conditions led to site-selective azidation of amino acids B1-phenylalanine and B29-lysine present in RHI. Subsequently, the azido-insulin analogs were used in azide-alkyne [3 + 2] cycloaddition reactions to synthesize a diverse array of triazole-based RHI bioconjugates that were found to be potent human insulin receptor binders. The utility of this method was further demonstrated by the concise and controlled synthesis of a heterotrisubstituted insulin conjugate.

Protecting group free radical C-H trifluoromethylation of peptides.

Two radical-based approaches have been developed to effect the trifluoromethylation of aryl C-H bonds in native peptides either using stoichiometric oxidant or visible light photoredox catalysis. The reported methods are able to derivatize tyrosine and tryptophan sidechains under biocompatible conditions, and a number of examples are reported involving fully unprotected peptides with up to 51 amino acids. The development of this chemistry adds to the growing array of chemical methods for selectively modifying amino acid residues in the context of complex peptides. The direct incorporation of trifluoromethyl groups into biopolymers enables the study of a range of biological and biochemical systems, and preliminary results indicate this method can be extended to the incorporation of other fluoroalkyl groups for bioconjugation applications.

Photoredox-Catalyzed Hydroxymethylation of Heteroaromatic Bases.

We report the development of a method for room-temperature C-H hydroxymethylation of heteroarenes. A key enabling advance in this work was achieved by implementing visible light photoredox catalysis that proved to be applicable to many classes of heteroarenes and tolerant of diverse functional groups found in druglike molecules.

Chemistry informer libraries: a chemoinformatics enabled approach to evaluate and advance synthetic methods.

Major new advances in synthetic chemistry methods are typically reported using simple, non-standardized reaction substrates, and reaction failures are rarely documented. This makes the evaluation and choice of a synthetic method difficult. We report a standardized complex molecule diagnostic approach using collections of relevant drug-like molecules which we call chemistry informer libraries. With this approach, all chemistry results, successes and failures, can be documented to compare and evolve synthetic methods. To aid in the visualization of chemistry results in drug-like physicochemical space we have used an informatics methodology termed principal component analysis. We have validated this method using palladium- and copper-catalyzed reactions, including Suzuki-Miyaura, cyanation and Buchwald-Hartwig amination.

Remote Meta-C-H Activation Using a Pyridine-Based Template: Achieving Site-Selectivity via the Recognition of Distance and Geometry.

The pyridyl group has been extensively employed to direct transition-metal-catalyzed C-H activation reactions in the past half-century. The typical cyclic transition states involved in these cyclometalation processes have only enabled the activation of ortho-C-H bonds. Here, we report that pyridine is adapted to direct meta-C-H activation of benzyl and phenyl ethyl alcohols through engineering the distance and geometry of a directing template. This template takes advantage of a stronger σ-coordinating pyridine to recruit Pd catalysts to the desired site for functionalization. The U-shaped structure accommodates the otherwise highly strained cyclophane-like transition state. This development illustrates the potential of achieving site selectivity in C-H activation via the recognition of distal and geometric relationship between existing functional groups and multiple C-H bonds in organic molecules.

Correction to "Remote Meta-C-H Activation Using a Pyridine-Based Template: Achieving Site-Selectivity via the Recognition of Distance and Geometry".

[This corrects the article DOI: 10.1021/acscentsci.5b00312.].

High-throughput purification platform in support of drug discovery.

The application of parallel synthesis is an efficient approach to explore the chemical space and to rapidly develop meaningful structure activity relationship (SAR) data for drug discovery programs. However, the effectiveness of the parallel synthesis requires a high throughput purification workflow that can process a large number of crude samples within a meaningful time frame. This paper describes a high throughput purification platform that has been adopted at Merck's Rahway research site. The platform includes the evaluation of crude samples, mass-directed HPLC purification, fraction analysis, compound registration, final compound purity assessment and assay distribution. Assisting with the sample tracking and the data management is the internally designed laboratory information management system, Light Automation Framework (LAF). Using this process and the tools described herein, the group has successfully achieved purities of 95% or greater for 90% of samples.

Design of a novel pyrrolidine scaffold utilized in the discovery of potent and selective human ß3 adrenergic receptor agonists.

A novel class of human ß(3)-adrenergic receptor agonists was designed in effort to improve selectivity and metabolic stability versus previous disclosed ß(3)-AR agonists. As observed, many of the ß(3)-AR agonists seem to need the acyclic ethanolamine core for agonist activity. We have synthesized derivatives that constrained this moiety by introduction of a pyrrolidine. This unique modification maintains human ß(3) functional potency with improved selectivity versus ancillary targets and also eliminates the possibility of the same oxidative metabolites formed from cleavage of the N-C bond of the ethanolamine. Compound 39 exhibited excellent functional ß(3) agonist potency across species with good pharmacokinetic properties in rat, dog, and rhesus monkeys. Early de-risking of this novel pyrrolidine core (44) via full AMES study supports further research into various new ß(3)-AR agonists containing the pyrrolidine moiety.

Heterocyclic acetamide and benzamide derivatives as potent and selective beta3-adrenergic receptor agonists with improved rodent pharmacokinetic profiles.

A series of amide derived beta(3)-adrenergic receptor (AR) agonists is described. The discovery and optimization of several series of compounds derived from 1, is used to lay the SAR foundation for second generation beta(3)-AR agonists for the treatment of overactive bladder.

A cascade approach to cyclic aminonitrones: reaction discovery, mechanism, and scope.

Treatment of omega-epoxynitriles with hydroxylamine affords cyclic aminonitrones in a single step and with high stereoselectivity. The scope of this novel transformation was explored in a series of examples. The aminonitrone products were shown to be useful substrates for further selective elaboration.

Synthesis and study of alendronate derivatives as potential prodrugs of alendronate sodium for the treatment of low bone density and osteoporosis.

Alendronate derivatives were evaluated as potential prodrugs for the osteoporosis drug alendronate sodium in an attempt to enhance the systemic exposure after oral administration. An investigation of the chemical behavior of alendronate derivatives led to development of practical synthetic strategies and prediction of each structural class's prodrug potential. Pharmacokinetic studies of N-myristoylalendronic acid revealed that 25% have been converted in vivo after i.v. administration in rat, providing an important proof-of-concept for this strategy.