Michael Raymond Collins

Practical and innate carbon-hydrogen functionalization of heterocycles

Nitrogen-rich heterocyclic compounds have had a profound effect on human health because these chemical motifs are found in a large number of drugs used to combat a broad range of diseases and pathophysiological conditions. Advances in transition-metal-mediated cross-coupling have simplified the synthesis of such molecules; however, C–H functionalization of medicinally important heterocycles that does not rely on pre-functionalized starting materials is an underdeveloped area. Unfortunately, the innate properties of heterocycles that make them so desirable for biological applications—such as aqueous solubility and their ability to act as ligands—render them challenging substrates for direct chemical functionalization. Here we report that zinc sulphinate salts can be used to transfer alkyl radicals to heterocycles, allowing for the mild (moderate temperature, 50 °C or less), direct and operationally simple formation of medicinally relevant C–C bonds while reacting in a complementary fashion to other innate C–H functionalization methods (Minisci, borono-Minisci, electrophilic aromatic substitution, transition-metal-mediated C–H insertion and C–H deprotonation). We prepared a toolkit of these reagents and studied their reactivity across a wide range of heterocycles (natural products, drugs and building blocks) without recourse to protecting-group chemistry. The reagents can even be used in tandem fashion in a single pot in the presence of water and air.

A New Reagent for Direct Difluoromethylation

Molecular scaffolds containing alkylfluorine substituents are desired in many areas of chemical research from materials to pharmaceuticals. Herein, we report the invention of a new reagent (Zn(SO(2)CF(2)H)(2), DFMS) for the innate difluoromethylation of organic substrates via a radical process. This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols. Regiochemical comparisons suggest that the CF(2)H radical generated from the new reagent possesses nucleophilic character.

Discovery of (10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]-benzoxadiazacyclotetradecine-3-carbonitrile (PF-06463922), a macrocyclic inhibitor of anaplastic lymphoma kinase (ALK) and c-ros oncogene 1 (ROS1) with preclinical brain exposure and broad-spectrum potency against ALK-resistant mutations.

Although crizotinib demonstrates robust efficacy in anaplastic lymphoma kinase (ALK)-positive non-small-cell lung carcinoma patients, progression during treatment eventually develops. Resistant patient samples revealed a variety of point mutations in the kinase domain of ALK, including the L1196M gatekeeper mutation. In addition, some patients progress due to cancer metastasis in the brain. Using structure-based drug design, lipophilic efficiency, and physical-property-based optimization, highly potent macrocyclic ALK inhibitors were prepared with good absorption, distribution, metabolism, and excretion (ADME), low propensity for p-glycoprotein 1-mediated efflux, and good passive permeability. These structurally unusual macrocyclic inhibitors were potent against wild-type ALK and clinically reported ALK kinase domain mutations. Significant synthetic challenges were overcome, utilizing novel transformations to enable the use of these macrocycles in drug discovery paradigms. This work led to the discovery of 8k (PF-06463922), combining broad-spectrum potency, central nervous system ADME, and a high degree of kinase selectivity.

C–H Methylation of Heteroarenes Inspired by Radical SAM Methyl Transferase

A practical C–H functionalization method for the methylation of heteroarenes is presented. Inspiration from Nature’s methylating agent, S-adenosylmethionine (SAM), allowed for the design and development of zinc bis(phenylsulfonylmethanesulfinate), or PSMS. The action of PSMS on a heteroarene generates a (phenylsulfonyl)methylated intermediate that can be easily separated from unreacted starting material. This intermediate can then be desulfonylated to the methylated product or elaborated to a deuteriomethylated product, and can divergently access medicinally important motifs. This mild, operationally simple protocol that can be conducted in open air at room temperature is compatible with sensitive functional groups for the late-stage functionalization of pharmacologically relevant substrates.

Simple Sulfinate Synthesis Enables CH Trifluoromethylcyclopropanation

A simple method to convert readily available carboxylic acids into sulfinate salts by employing an interrupted Barton decarboxylation reaction is reported. A medicinally oriented panel of ten new sulfinate reagents was created using this method, including a key trifluoromethylcyclopropanation reagent, TFCS-Na. The reactivity of six of these salts towards C-H functionalization was field-tested using several different classes of heterocycles.

Strain-release amination

Opening one ring to tack on another Curious chemists have long sought to learn just how tightly carbon atoms can be bound together. For instance, its possible to form a bond between two opposite corners of an already strained four-membered ring to make an edge-sharing pair of triangles. Gianatassio et al. have now devised a general use for these and related molecular curiosities. They show that appropriately modified nitrogen centers can pop open the most highly strained bond, leaving the more modestly strained ring motif intact. In this way, small rings can emerge as a convenient diversifying element in compounds, including new pharmaceutical candidates. Science, this issue p. 241 Strained rings are appended to compounds of pharmaceutical interest through the use of even more highly strained precursors. To optimize drug candidates, modern medicinal chemists are increasingly turning to an unconventional structural motif: small, strained ring systems. However, the difficulty of introducing substituents such as bicyclo[1.1.1]pentanes, azetidines, or cyclobutanes often outweighs the challenge of synthesizing the parent scaffold itself. Thus, there is an urgent need for general methods to rapidly and directly append such groups onto core scaffolds. Here we report a general strategy to harness the embedded potential energy of effectively spring-loaded C–C and C–N bonds with the most oft-encountered nucleophiles in pharmaceutical chemistry, amines. Strain-release amination can diversify a range of substrates with a multitude of desirable bioisosteres at both the early and late stages of a synthesis. The technique has also been applied to peptide labeling and bioconjugation.

Design of Potent and Selective Inhibitors to Overcome Clinical Anaplastic Lymphoma Kinase Mutations Resistant to Crizotinib.

Crizotinib (1), an anaplastic lymphoma kinase (ALK) receptor tyrosine kinase inhibitor approved by the U.S. Food and Drug Administration in 2011, is efficacious in ALK and ROS positive patients. Under pressure of crizotinib treatment, point mutations arise in the kinase domain of ALK, resulting in resistance and progressive disease. The successful application of both structure-based and lipophilic-efficiency-focused drug design resulted in aminopyridine 8e, which was potent across a broad panel of engineered ALK mutant cell lines and showed suitable preclinical pharmacokinetics and robust tumor growth inhibition in a crizotinib-resistant cell line (H3122-L1196M).

Dihydroxylphenyl amides as inhibitors of the Hsp90 molecular chaperone.

Information from X-ray crystal structures were used to optimize the potency of a HTS hit in a Hsp90 competitive binding assay. A class of novel and potent small molecule Hsp90 inhibitors were thereby identified. Enantio-pure compounds 31 and 33 were potent in PGA-based competitive binding assay and inhibited proliferation of various human cancer cell lines in vitro, with IC(50) values averaging 20 nM.

Preparation and purification of zinc sulfinate reagents for drug discovery

The present protocol details the synthesis of zinc bis(alkanesulfinate)s that can be used as general reagents for the formation of radical species. The zinc sulfinates described herein are generated from the corresponding sulfonyl chlorides by treatment with zinc dust. The products may be used crude, or a simple purification procedure may be performed to minimize incorporation of water and zinc chloride. Although the synthesis of the zinc sulfinate salts can generally be completed within 3 h, workup can take up to 24 h and purification can take up to 3 h. Following the steps in this protocol would enable the user to generate a small toolkit of zinc sulfinate reagents over the course of 1 week.

A Simple Litmus Test for Aldehyde Oxidase Metabolism of Heteroarenes

The bioavailability of aromatic azaheterocyclic drugs can be affected by the activity of aldehyde oxidase (AO). Susceptibility to AO metabolism is difficult to predict computationally and can be complicated in vivo by differences between species. Here we report the use of bis(((difluoromethyl)sulfinyl)oxy)zinc (DFMS) as a source of CF2H radical for a rapid and inexpensive chemical “litmus test” for the early identification of heteroaromatic drug candidates that have a high probability of metabolism by AO.