Copper-Mediated N-Cyclopropylation of Azoles, Amides, and Sulfonamides by Cyclopropylboronic Acid

Stereospecific Enzymatic Conversion of Boronic Acids to Amines

Boronic acids and esters are highly regarded for their safety, unique reactivity, and versatility in synthesizing a wide range of small molecules, bioconjugates, and materials. They are not exploited in biocatalytic synthesis, however, because enzymes that can make, break, or modify carbon-boron bonds are rare. We wish to combine the advantages of boronic acids and esters for molecular assembly with biocatalysis, which offers the potential for unsurpassed selectivity and efficiency. Here, we introduce an engineered protoglobin nitrene transferase that catalyzes the new-to-nature amination of boronic acids using hydroxylamine. Initially targeting aryl boronic acids, we show that the engineered enzyme can produce a wide array of anilines with high yields and total turnover numbers (up to 99% yield and >4000 TTN), with water and boric acid as the only byproducts. We also demonstrate that the enzyme is effective with bench-stable boronic esters, which hydrolyze in situ to their corresponding boronic acids. Exploring the enzyme's capacity for enantioselective catalysis, we found that a racemic alkyl boronic ester affords an enantioenriched alkyl amine, a transformation not achieved with chemocatalysts. The formation of an exclusively unrearranged product during the amination of a boronic ester radical clock and the reaction's stereospecificity support a two-electron process akin to a 1,2-metallate shift mechanism. The developed transformation enables new biocatalytic routes for synthesizing chiral amines.

Metal-Free Hydroxymethylation of Indole Derivatives with Formic Acid as an Alternative Way to Indirect Utilization of CO2

The selective N-alkylation of indole substrates remains an ongoing research challenge for the relative attenuated nucleophilicity toward nitrogen. Herein, we developed the hydroxymethylation of indole derivatives to afford N-alkylated indole products with formic acid. This metal-free process was promoted by the organic base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) using phenylsilane as the reductant under mild conditions. Besides, this strategy represents an alternative way for indirect utilization of CO₂, considering the facile hydrogenation of CO₂ to produce HCOOH.

Copper-catalyzed three-component N-alkylation of quinazolinones and azoles

A Cu-catalyzed three-component N-alkylated coupling reaction of N-heteroarenes with methyl ketones and one carbon source has been developed. Using methyl ketones as alkylation reagent and DMPA (N,N’-dimethylpropionamide) as one carbon...

Formation of the Tertiary Sulfonamide C(sp3)-N Bond Using Alkyl Boronic Ester via Intramolecular and Intermolecular Copper-Catalyzed Oxidative Cross-Coupling

A synthetic strategy for the formation of C(sp³)-N bonds, particularly through a copper-catalyzed oxidative cross-coupling, is rare. Herein, we report a novel synthetic approach for the preparation of tertiary sulfonamides via copper-catalyzed intra- and intermolecular oxidative C(sp³)-N cross-coupling reactions. This method allows the utilization of the readily available C(sp³)-based pinacol boronate as a substrate and the tolerance of a wide range of functional groups under mild reaction conditions. The success of this strategy relies on the unprecedented additive effects of silanol and NaIO₄.

Chan-Lam Amination of Secondary and Tertiary Benzylic Boronic Esters

We report a Chan-Lam coupling reaction of benzylic and allylic boronic esters with primary and secondary anilines to form valuable alkyl amine products. Both secondary and tertiary boronic esters can be used as coupling partners, with mono-alkylation of the aniline occurring selectively. This is a rare example of a transition-metal-mediated transformation of a tertiary alkylboron reagent. Initial investigation into the reaction mechanism suggests that transmetalation from B to Cu occurs through a single-electron, rather than a two-electron process.

A General N-alkylation Platform via Copper Metallaphotoredox and Silyl Radical Activation of Alkyl Halides

The catalytic union of amides, sulfonamides, anilines, imines or N-heterocycles with a broad spectrum of electronically and sterically diverse alkyl bromides has been achieved via a visible light-induced metallaphotoredox platform. The use of a halogen abstraction-radical capture (HARC) mechanism allows for room temperature coupling of C(sp³ )-bromides using simple Cu(II) salts, effectively bypassing the prohibitively high barriers typically associated with thermally-induced S_N2 or S_N1 N-alkylation. This regio- and chemoselective protocol is compatible with >10 classes of medicinally-relevant N-nucleophiles, including established pharmaceutical agents, in addition to structurally diverse primary, secondary and tertiary alkyl bromides. Furthermore, the capacity of HARC methodologies to engage conventionally inert coupling partners is highlighted via the union of N-nucleophiles with cyclopropyl bromides and unactivated alkyl chlorides, substrates that are incompatible with nucleophilic substitution pathways. Preliminary mechanistic experiments validate the dual catalytic, open-shell nature of this platform, which enables reactivity previously unattainable in traditional halide-based N-alkylation systems.

Synthesis of aryl cyclopropyl sulfides through copper-promoted S-cyclopropylation of thiophenols using cyclopropylboronic acid

The copper-promoted S-cyclopropylation of thiophenols using cyclopropylboronic acid is reported. The procedure operates under simple conditions to afford the corresponding aryl cyclopropyl sulfides in moderate to excellent yields. The reaction tolerates substitution in ortho-, meta- and para-substitution as well as electron-donating and electron-withdrawing groups. The S-cyclopropylation of a thiophenol was also accomplished using potassium cyclopropyl trifluoroborate.

N,O-Bidentate ligand-tunable copper(ii) complexes as a catalyst for Chan-Lam coupling reactions of arylboronic acids with 1H-imidazole derivatives

An efficient procedure for Chan-Lam coupling reactions of arylboronic acids with 1H-imidazole derivatives using N,O-bidentate ligand-tunable copper(ii) complexes as a catalyst under base-free conditions has been developed. This protocol features mild reaction conditions, high yields and compatibility with different functional groups, providing a direct and facile strategy for the construction of C-N bonds and synthesis of heterocyclic compounds.

[3,3]-Sigmatropic Rearrangement of Cyclopropenylcarbinyl Cyanates: Access to Alkylidene(aminocyclopropane) Derivatives

Cyclopropenylcarbinyl cyanates, generated in situ by dehydration of the corresponding carbamates, underwent an efficient and stereoselective [3,3]-sigmatropic rearrangement leading to the corresponding alkylidene(isocyanatocyclopropanes), which could be converted into various alkylidene(aminocyclopropane) derivatives in a one-pot manner. This transformation complements the repertoire of sigmatropic rearrangements involving cyclopropenylcarbinol derivatives and in particular, the previously reported Overman rearrangement of cyclopropenylcarbinyl trichloroacetimidates.

AIEgen-Functionalized Mesoporous Silica Gated by Cyclodextrin-Modified CuS for Cell Imaging and Chemo-Photothermal Cancer Therapy

A novel multifunctional drug delivery system has been constructed by assembling per-6-thio-β-cyclodextrin-modified ultrasmall CuS nanoparticles (CD-CuS) onto fluorescent AIEgen-containing mesoporous silica nanoparticles (FMSN). The CD-CuS nanoparticles are anchored on the surface of benzimidazole-grafted FMSN, acting as a gatekeeper and photothermal agent. The prepared blue-emitting nanocomposite (FMSN@CuS) exhibits good biocompatibility and cell imaging capability. Anticancer drug doxorubicin hydrochloride (DOX) molecules are loaded into FMSN@CuS, and zero prerelease at physiological pH (7.4) and on-demand drug release at an acidic environment can be achieved due to the pH-responsive gate-opening of CD-CuS only at an acidic condition. The FMSN@CuS nanocomposite can generate obvious thermal effect after the exposure of 808 nm laser, which can also accelerate the DOX release. Meanwhile, the fluorescence intensity of DOX-loaded FMSN@CuS increases with the release of DOX, and the intracellular drug release process can be tracked according to the change of luminescence intensity. More importantly, DOX-loaded FMSN@CuS displays efficient anticancer effects in vitro upon 808 nm laser irradiation, demonstrating a good synergistic therapeutic effect via combining enhanced chemotherapy and photothermal therapy.

Discovery and Characterization of CD12681, a Potent RORγ Inverse Agonist, Preclinical Candidate for the Topical Treatment of Psoriasis

With possible implications in multiple autoimmune diseases, the retinoic acid receptor-related orphan receptor RORγ has become a sought-after target in the pharmaceutical industry. Herein are described the efforts to identify a potent RORγ inverse agonist compatible with topical application for the treatment of skin diseases. These efforts culminated in the discovery of N-(2,4-dimethylphenyl)-N-isobutyl-2-oxo-1-[(tetrahydro-2H-pyran-4-yl)methyl]-2,3-dihydro-1H-benzo[d]imidazole-5-sulfonamide (CD12681), a potent inverse agonist with in vivo activity in an IL-23-induced mouse skin inflammation model.

Copper-Catalyzed Amidation of Primary and Secondary Alkyl Boronic Esters

The oxidative copper-catalyzed cross-coupling of functionalized alkyl boronic esters with primary amides is reported. Through the identification of appropriate diketimine ligands, conditions for efficient coupling of both primary and secondary alkyl boronic esters with diverse primary amides, including acetamide, have been developed.

Direct N-cyclopropylation of secondary acyclic amides promoted by copper

The N-cyclopropylation of aromatic and aliphatic secondary acyclic amides, known to be poor nucleophiles, has been accomplished using a simple and cheap copper system. The corresponding tertiary acyclic amides, which constitute a wide family of biologically active compounds, have been obtained in good to excellent yields.

Selective formation of secondary amides via the copper-catalyzed cross-coupling of alkylboronic acids with primary amides

For the first time, a general catalytic procedure for the cross-coupling of primary amides and alkylboronic acids is demonstrated. The key to the success of this reaction was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the monoalkylation of amides.

Palladium-catalyzed α-arylation of 2-chloroacetates and 2-chloroacetamides

A method has been developed for the Pd-catalyzed synthesis of α-(hetero)aryl esters and amides through a Suzuki-Miyaura cross-coupling reaction. This method avoids the use of strong base, does not necessitate inert or low temperature formation of reagents, and does not require the use of a large excess of organometallic reagent. Utilization of organotrifluoroborate salts as nucleophilic partners allows a variety of functional groups and heterocyclic compounds to be tolerated.

C-N bond formation under Cu-catalysis: synthesis and in vitro evaluation of N-aryl substituted thieno[2,3-d]pyrimidin-4(3H)-ones against chorismate mutase

A series of novel N-aryl substituted thieno[2,3-d]pyrimidin-4(3H)-ones were designed and synthesized as potential inhibitors of chorismate mutase. Synthesis of this class of compounds was carried out by using Cu-mediated C-N bond forming reaction between thieno[2,3-d]pyrimidin-4(3H)-ones and aryl boronic acids. The reaction can be performed in an open flask as the conversion was found to be not sensitive to the presence of air or atmospheric moisture. A range of compounds were prepared by using this method and single crystal X-ray diffraction study was performed using a representative compound. In vitro pharmacological data of some of the compounds synthesized along with dose response studies using active molecules are presented. In silico interactions of these molecules with chorismate mutase are also presented.

Copper-mediated oxidative trifluoromethylation of boronic acids

A copper-mediated oxidative cross-coupling of aryl- and alkenylboronic acids with (trifluoromethyl)trimethylsilane (Me(3)SiCF(3)) under mild conditions has been developed. This method allows a wide range of functional group tolerant trifluoromethylated arenes and alkenes to be easily prepared. This oxidative trifluoromethylation has the potential to introduce trifluoromethyl groups into advanced, highly functionalized organic molecules.

Copper-promoted N-cyclopropylation of anilines and amines by cyclopropylboronic acid

Reaction of anilines, primary and secondary aliphatic amines with cyclopropylboronic acid in dichloroethane in the presence of Cu(OAc)(2) (1 equiv.), 2,2'-bipyridine (1 equiv.) and sodium carbonate or sodium bicarbonate (2 equiv.) under air atmosphere afforded the corresponding N-cyclopropyl derivatives in good to excellent yields.