Decarboxylative Amination: Diazirines as Single and Double Electrophilic Nitrogen Transfer Reagents.

The ubiquity of nitrogen-containing small molecules in medicine necessitates the continued search for improved methods for C-N bond formation. Electrophilic amination often requires a disparate toolkit of reagents whose selection depends on the specific structure and functionality of the substrate to be aminated. Further, many of these reagents are challenging to handle, engage in undesired side reactions, and function only within a narrow scope. Here we report the use of diazirines as practical reagents for the decarboxylative amination of simple and complex redox-active esters. The diaziridines thus produced are readily diversifiable to amines, hydrazines, and nitrogen-containing heterocycles in one step. The reaction has also been applied in fluorous phase synthesis with a perfluorinated diazirine.

Strain-Release Heteroatom Functionalization: Development, Scope, and Stereospecificity.

Driven by the ever-increasing pace of drug discovery and the need to push the boundaries of unexplored chemical space, medicinal chemists are routinely turning to unusual strained bioisosteres such as bicyclo[1.1.1]pentane, azetidine, and cyclobutane to modify their lead compounds. Too often, however, the difficulty of installing these fragments surpasses the challenges posed even by the construction of the parent drug scaffold. This full account describes the development and application of a general strategy where spring-loaded, strained C-C and C-N bonds react with amines to allow for the "any-stage" installation of small, strained ring systems. In addition to the functionalization of small building blocks and late-stage intermediates, the methodology has been applied to bioconjugation and peptide labeling. For the first time, the stereospecific strain-release "cyclopentylation" of amines, alcohols, thiols, carboxylic acids, and other heteroatoms is introduced. This report describes the development, synthesis, scope of reaction, bioconjugation, and synthetic comparisons of four new chiral "cyclopentylation" reagents.

A unified approach to ent-atisane diterpenes and related alkaloids: synthesis of (-)-methyl atisenoate, (-)-isoatisine, and the hetidine skeleton.

A unified approach to ent-atisane diterpenes and related atisine and hetidine alkaloids has been developed from ent-kaurane (-)-steviol (1). The conversion of the ent-kaurane skeleton to the ent-atisane skeleton features a Mukaiyama peroxygenation with concomitant cleavage of the C13-C16 bond. Conversion to the atisine skeleton (9) features a C20-selective C-H activation using a Suárez modification of the Hofmann-Löffler-Freytag (HLF) reaction. A cascade sequence involving azomethine ylide isomerization followed by Mannich cyclization forms the C14-C20 bond in the hetidine skeleton (8). Finally, attempts to form the N-C6 bond of the hetisine skeleton (7) with a late-stage HLF reaction are discussed. The synthesis of these skeletons has enabled the completion of (-)-methyl atisenoate (3) and (-)-isoatisine (4).

Methyl 1-benzyl-5-methyl-2,4-diphenyl-1H-pyrrole-3-carboxyl-ate.

In the title compound, C26H23NO2, the dihedral angles between the pyrrole ring and the two phenyl rings are 58.1 (6) and 71.5 (5)°. The mean planes of the 5-methyl-benzene ring and the carboxyl group are twisted by 89.5 (3) and 22.1 (9)°, respectively, from the pyrrole ring. In the crystal, weak C-H⋯O inter-actions lead to supra-molecular layers in the ab plane.

Divergent synthesis of complex withanolides enabled by a scalable route and late-stage functionalization.

Withanolides are a group of naturally occurring C28 steroids based on an ergostane skeleton. They have a high degree of polyoxygenation, and the abundance of O-functional groups has enabled various natural alterations to both the carbocyclic skeleton and the side chain. Consequently, these molecules have intricate structural features that lead to their highly varied display of biological activities including anticancer, anti-inflammatory, and immunomodulating properties. Despite being intriguing leads for further discovery research, synthetic access to the withanolides remains highly challenging-compounds for current biological research are mainly isolated from plants, often inefficiently. Here, we report the divergent synthesis of 11 withanolides in 12 to 20 steps, enabled by a gram-scale route and a series of late-stage functionalizations, most notably a bioinspired photooxygenation-allylic hydroperoxide rearrangement sequence. This approach enables further biological research disconnected from a reliance on minute quantities of the parent natural products or their simple derivatives.

Regioselective hydroamination of unactivated olefins with diazirines as a diversifiable nitrogen source.

Nitrogen-containing compounds, such as amines, hydrazines, and heterocycles, play an indispensable role in medicine, agriculture, and materials. Alkylated derivatives of these compounds, especially in sterically congested environments, remain a challenge to prepare. Here we report a versatile method for the regioselective hydroamination of readily available unactivated olefins with diazirines. Over fifty examples are reported, including the protecting group-free amination of fourteen different natural products. A broad functional group tolerance includes alcohols, ketones, aldehydes, and epoxides. The proximate products of these reactions are diaziridines, which, under mild conditions, are converted to primary amines, hydrazines, and heterocycles. Five target- and diversity-oriented syntheses of pharmaceutical compounds are shown, along with the preparation of a bis-15N diazirine validated in the late-stage isotopic labeling of an RNA splicing modulator candidate. In this work, we report using diazirine (1) as an electrophilic nitrogen source in a regioselective hydroamination reaction, and the diversification of the resulting diaziridines.

Asymmetric synthesis of sulfoximines, sulfonimidoyl fluorides and sulfonimidamides enabled by an enantiopure bifunctional S(VI) reagent.

An increased interest to expand three-dimensional chemical space for the design of new materials and medicines has created a demand for isosteric replacement groups of commonly used molecular functionality. The structural and chemical properties of chiral S(VI) functional groups provide unique spatial and electronic features compared with their achiral sulfur- and carbon-based counterparts. Manipulation of the S(VI) centre to introduce structural variation with stereochemical control has remained a synthetic challenge. The stability of sulfonimidoyl fluorides and the efficiency of sulfur fluorine exchange chemistry has enabled the development of the enantiopure bifunctional S(VI) transfer reagent t-BuSF to overcome current synthetic limitations. Here, we disclose a reagent platform that serves as a chiral sulfur fluorine exchange template for the rapid asymmetric synthesis of over 70 sulfoximines, sulfonimidoyl fluorides and sulfonimidamides with excellent enantiomeric excess and good overall yields. Furthermore, the practical utility of the bifunctional S(VI) transfer reagent was demonstrated in the syntheses of enantiopure pharmaceutical intermediates and analogues.

Direct catalytic photodecarboxylative amination of carboxylic acids with diazirines for divergent access to nitrogen-containing compounds.

Amines, hydrazines, and nitrogen-containing heterocycles are pivotal species in medicine, agriculture, fine chemicals, and materials. Diazirines have been recently reported to serve as versatile electrophilic amination reagents for the synthesis of building blocks or late-stage C-N bond formation. Here, we report the catalytic photodecarboxylative amination of carboxylic acids with diazirines under mild conditions. The substrate scope includes broad functional group tolerance, such as ketones, esters, olefins, and alcohols, along with the late-stage amination of naproxen, ibuprofen, gemfibrozil, and gibberellic acid. Synthetic applications leverage the versatility of the intermediate diaziridines and include the regioselective preparation of a suite of 1H-indazoles, 2H-indazoles, and fluoroquinolones.

Strain-release driven reactivity of a chiral SuFEx reagent provides stereocontrolled access to sulfinamides, sulfonimidamides, and sulfoximines.

Efforts aimed at enriching the chemical and structural diversity of small molecules have invigorated synthetic exploration in the last two decades. Spatially defined molecular functionality serves as the foundation to construct unique chemical space to further advance discovery science. The chiral SuFEx reagent t-BuSF provides a modular platform for the stereocontrolled bifunctionalization of sulfur. Here we report a third functional feature of t-BuSF enabled by carbamoyl torsional strain-release that further expands the S(IV) and S(VI) chemical space accessible as showcased in over seventy examples, multiple applications in medicinal chemistry, organocatalysis, and diversity-oriented synthesis. The methods presented herein allow for rapid asymmetric diversification around a stereodefined sulfur center with readily available building blocks, improving upon the current state-of-the-art for sulfinyl and sulfonimidoyl synthesis.

Bruceolline D: 3,3-dimethyl-1H,4H-cyclo-penta-[b]indol-2(3H)-one.

The title compound, C13H13NO, crystallizes with four independent mol-ecules in the asymmetric unit. The 12-membered penta-[b]indole rings are essentially planar, with maximum deviations ranging from 0.034 (4) to 0.036 (4) Šin the four unique mol-ecules. In the crystal, weak C-H⋯O inter-actions are observed, which link the mol-ecules into chains along [010].

Bruceolline J: 2-hy-droxy-3,3-dimethyl-2,3-di-hydro-cyclo-penta-[b]indol-1(4H)-one.

The 12-membered cyclo-penta-[b]indole ring system in the title compound, C13H13NO2, deviates only slightly from planarity (r.m.s. deviation = 0.051 Å). In the crystal, N-H⋯O and O-H⋯O hydrogen bonds link the mol-ecules into sheets parallel to (100). The five-membered cyclopentanone ring is in slightly distorted envelope conformation with the C atom bearing the hydroxy substituent as the flap.

Stereospecific α-(hetero)arylation of sulfoximines and sulfonimidamides.

The occurrence of sulfoximines and sulfonimidoyl groups in biologically active molecules within pharmaceuticals and agrochemicals has notably increased in the past decade. This increase has prompted a wave of discovery of methods to install S(VI) functionality into complex organic molecules. Traditional synthetic methods to form α-substituted sulfonimidoyl motifs rely on S-C bond disconnections and typically require control of the stereogenic S-centre or late-stage modification at sulfur, and comprise multistep routes. Here, we report the development of a stereospecific, modular SNAr approach for the introduction of sulfonimidoyl functional groups into heterocyclic cores. This strategy has been demonstrated across 85 examples, in good to excellent yield, of complex and diverse heterocycles. Sulfoximines, sulfonimidamides and sulfondiimines are all compatible nucleophiles in the SNAr reaction and hence, the methodology was applied to the synthesis of four sulfoximine-containing pharmaceuticals. Of these synthetic applications, most notably ceralasertib, an ATR inhibitor currently in clinical trials, was synthesized in an eight-step procedure on a gram-scale.

Discovery of Dual TAF1-ATR Inhibitors and Ligand-Induced Structural Changes of the TAF1 Tandem Bromodomain.

Bromodomains regulate chromatin remodeling and gene transcription through recognition of acetylated lysines on histones and other proteins. Bromodomain-containing protein TAF1, a subunit of general transcription factor TFIID, initiates preinitiation complex formation and cellular transcription. TAF1 serves as a cofactor for certain oncogenic transcription factors and is implicated in regulating the p53 tumor suppressor. Therefore, TAF1 is a potential target to develop small molecule therapeutics for diseases arising from dysregulated transcription, such as cancer. Here, we report the ATR kinase inhibitor AZD6738 (Ceralasertib) and analogues thereof as bona fide inhibitors of TAF1. Crystallographic and small-angle X-ray scattering studies established that newly identified and previously reported inhibitors stabilize distinct structural states of the TAF1 tandem bromodomain through "open-closed" transitions and dimerization. Combined with functional studies on p53 signaling in cancer cell lines, the data provide new insights into the feasibility and challenges of TAF1 inhibitors as chemical probes and therapeutics.

New synthetic triterpenoids: potent agents for prevention and treatment of tissue injury caused by inflammatory and oxidative stress.

We review the original rationale for the development and the chemistry of a series of new synthetic oleanane triterpenoids (SO), based on oleanolic acid (1) as a starting material. Many of the new compounds that have been made, such as 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid ("CDDO", 8), are highly potent (activities found at levels below 1 nM) anti-inflammatory agents, as measured by their ability to block the cellular synthesis of the enzyme inducible nitric oxide synthase (iNOS) in activated macrophages. Details of the organic synthesis of new SO and their chemical mechanisms of biological activity are reviewed, as is formation of biotin conjugates for investigation of protein targets. Finally, we give a brief summary of important biological activities of SO in many organ systems in numerous animal models. Clinical investigation of a new SO (methyl 2-cyano-3,12-dioxooleana-1,9(11)dien-28-oate, "CDDO-Me", bardoxolone methyl, 13) is currently in progress.

Photodecarboxylative Amination of Redox-Active Esters with Diazirines.

Diazirines have been recently demonstrated to serve as electrophilic amination reagents that afford diaziridines, versatile heterocycles that are readily transformed into amines, hydrazines, and nitrogen-containing heterocycles. Here, we report the photodecarboxylative amination of redox-active esters with diazirines using inexpensive photoactivators under mild conditions with an enhanced scope for primary substrates. The stability of diazirines to blue light is demonstrated, paving the way for further research into other photochemical amination methods with these unique heterocycles.

Organic chemistry. Strain-release amination.

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.

What controls regiochemistry in 1,3-dipolar cycloadditions of münchnones with nitrostyrenes?

The distinct experimentally observed regiochemistries of the reactions between mesoionic münchnones and ß-nitrostyrenes or phenylacetylene are shown by DFT/BDA/ETS-NOCV analyses of the transition states to be dominated by steric and reactant reorganization factors, rather than the orbital overlap considerations predicted by Frontier Molecular Orbital (FMO) Theory.

A short, protecting group-free total synthesis of bruceollines D, E, and J.

A short, protecting group-free total synthesis of bruceollines D, E, and J has been achieved. The enantioselective reduction of bruceolline E with ß-chlorodiisopinocampheylborane delivers both the natural and unnatural enantiomers of bruceolline J in excellent yields and enantioselectivities. Reduction with baker's yeast and sucrose was shown to provide the unnatural enantiomer of bruceolline J in 98% ee.