µMap Photoproximity Labeling Enables Small Molecule Binding Site Mapping.

The characterization of ligand binding modes is a crucial step in the drug discovery process and is especially important in campaigns arising from phenotypic screening, where the protein target and binding mode are unknown at the outset. Elucidation of target binding regions is typically achieved by X-ray crystallography or photoaffinity labeling (PAL) approaches; yet, these methods present significant challenges. X-ray crystallography is a mainstay technique that has revolutionized drug discovery, but in many cases structural characterization is challenging or impossible. PAL has also enabled binding site mapping with peptide- and amino-acid-level resolution; however, the stoichiometric activation mode can lead to poor signal and coverage of the resident binding pocket. Additionally, each PAL probe can have its own fragmentation pattern, complicating the analysis by mass spectrometry. Here, we establish a robust and general photocatalytic approach toward the mapping of protein binding sites, which we define as identification of residues proximal to the ligand binding pocket. By utilizing a catalytic mode of activation, we obtain sets of labeled amino acids in the proximity of the target protein binding site. We use this methodology to map, in vitro, the binding sites of six protein targets, including several kinases and molecular glue targets, and furthermore to investigate the binding site of the STAT3 inhibitor MM-206, a ligand with no known crystal structure. Finally, we demonstrate the successful mapping of drug binding sites in live cells. These results establish µMap as a powerful method for the generation of amino-acid- and peptide-level target engagement data.

A Chiral Amine Transfer Approach to the Photocatalytic Asymmetric Synthesis of α-Trialkyl-α-tertiary Amines.

A long-standing challenge within radical chemistry is that of controlling the absolute stereochemistry of the products. Here, we report the stereocontrolled addition of α-amino radicals reductively generated from imines via visible-light-mediated photoredox-catalysis to alkenes, giving rise to enantioenriched α-trialkyl-α-tertiary amines. This process exploits a commercially available phenylglycinol derivative as a source of both nitrogen and chiral information. DFT studies support a stereochemical model whereby an intramolecular H-bond rigidifies the transition state of the enantiodetermining step.

Small molecule photocatalysis enables drug target identification via energy transfer.

Over half of new therapeutic approaches fail in clinical trials due to a lack of target validation. As such, the development of new methods to improve and accelerate the identification of cellular targets, broadly known as target ID, remains a fundamental goal in drug discovery. While advances in sequencing and mass spectrometry technologies have revolutionized drug target ID in recent decades, the corresponding chemical-based approaches have not changed in over 50 y. Consigned to outdated stoichiometric activation modes, modern target ID campaigns are regularly confounded by poor signal-to-noise resulting from limited receptor occupancy and low crosslinking yields, especially when targeting low abundance membrane proteins or multiple protein target engagement. Here, we describe a broadly general platform for photocatalytic small molecule target ID, which is founded upon the catalytic amplification of target-tag crosslinking through the continuous generation of high-energy carbene intermediates via visible light-mediated Dexter energy transfer. By decoupling the reactive warhead tag from the small molecule ligand, catalytic signal amplification results in unprecedented levels of target enrichment, enabling the quantitative target and off target ID of several drugs including (+)-JQ1, paclitaxel (Taxol), dasatinib (Sprycel), as well as two G-protein-coupled receptors-ADORA2A and GPR40.

Thiol-Mediated α-Amino Radical Formation via Visible-Light-Activated Ion-Pair Charge-Transfer Complexes.

Visible-light-activated electron donor-acceptor complexes offer distinct reaction pathways for the synthesis of complex molecules under mild conditions. Herein, we report a method for the reductive generation of α-amino radicals via the reaction of a visible-light-activated ion-pair charge-transfer complex formed between an in situ-generated alkyl-iminium ion and a thiophenolate. This distinct activation mode is demonstrated through the development of a multicomponent coupling reaction to form substituted aminomethyl-cyclopentanes from secondary amines, cyclopropyl aldehydes, and alkenes. The operationally straightforward transformation displays broad scope and provides a means to generate cyclic amine-containing scaffolds from readily available feedstocks.

Reactive intermediates for interactome mapping.

The interactions of biomolecules underpin all cellular processes, and the understanding of their dynamic interplay can lead to significant advances in the treatment of disease through the identification of novel therapeutic strategies. Protein-protein interactions (PPIs) in particular play a vital role within this arena, providing the basis for the majority of cellular signalling pathways. Despite their great importance, the elucidation of weak or transient PPIs that cannot be identified by immunoprecipitation remains a significant challenge, particularly in a disease relevant cellular environment. Recent approaches towards this goal have utilized the in situ generation of high energy intermediates that cross-link with neighboring proteins, providing a snapshot of the biomolecular makeup of the local area or microenvironment, termed the interactome. In this tutorial review, we discuss these reactive intermediates, how they are generated, and the impact they have had on the discovery of new biology. Broadly, we believe this strategy has the potential to significantly accelerate our understanding of PPIs and how they affect cellular physiology.

New Strategies for the Transition-Metal Catalyzed Synthesis of Aliphatic Amines.

Transition-metal catalyzed reactions that are able to construct complex aliphatic amines from simple, readily available feedstocks have become a cornerstone of modern synthetic organic chemistry. In light of the ever-increasing importance of aliphatic amines across the range of chemical sciences, this review aims to provide a concise overview of modern transition-metal catalyzed approaches to alkylamine synthesis and their functionalization. Selected examples of amine bond forming reactions include: (a) hydroamination and hydroaminoalkylation, (b) transition-metal catalyzed C(sp3)-H functionalization, and (c) transition-metal catalyzed visible-light-mediated light photoredox catalysis.

Rapid Syntheses of (-)-FR901483 and (+)-TAN1251C Enabled by Complexity-Generating Photocatalytic Olefin Hydroaminoalkylation.

We report a common strategy to facilitate the syntheses of the polycyclic alkaloids (-)-FR901483 (1) and (+)-TAN1251C (2). A divergent synthetic strategy provides access to both natural products through a pivotal spirolactam intermediate (3), which can be accessed on a gram-scale. A photocatalytic olefin hydroaminoalkylation brings together three readily available building blocks and forges the majority of the carbon framework present in 1 and 2 in a single operation, leading to concise total syntheses. The complexity-generating photocatalytic process also provides direct access to novel non-racemic spirolactam scaffolds that are likely to be of interest to early-stage drug discovery programs.

Streamlined Synthesis of C(sp3)-Rich N-Heterospirocycles Enabled by Visible-Light-Mediated Photocatalysis.

We report a general visible-light-mediated strategy that enables the construction of complex C(sp3)-rich N-heterospirocycles from feedstock aliphatic ketones and aldehydes with a broad selection of alkene-containing secondary amines. Key to the success of this approach was the utilization of a highly reducing Ir-photocatalyst and orchestration of the intrinsic reactivities of 1,4-cyclohexadiene and Hantzsch ester. This methodology provides streamlined access to complex C(sp3)-rich N-heterospirocycles displaying structural and functional features relevant to fragment-based lead identification programs.

Multicomponent synthesis of tertiary alkylamines by photocatalytic olefin-hydroaminoalkylation.

There is evidence to suggest that increasing the level of saturation (that is, the number of sp3-hybridized carbon atoms) of small molecules can increase their likelihood of success in the drug discovery pipeline1. Owing to their favourable physical properties, alkylamines have become ubiquitous among pharmaceutical agents, small-molecule biological probes and pre-clinical candidates2. Despite their importance, the synthesis of amines is still dominated by two methods: N-alkylation and carbonyl reductive amination3. Therefore, the increasing demand for saturated polar molecules in drug discovery has continued to drive the development of practical catalytic methods for the synthesis of complex alkylamines4-7. In particular, processes that transform accessible feedstocks into sp3-rich architectures provide a strategic advantage in the synthesis of complex alkylamines. Here we report a multicomponent, reductive photocatalytic technology that combines readily available dialkylamines, carbonyls and alkenes to build architecturally complex and functionally diverse tertiary alkylamines in a single step. This olefin-hydroaminoalkylation process involves a visible-light-mediated reduction of in-situ-generated iminium ions to selectively furnish previously inaccessible alkyl-substituted α-amino radicals, which subsequently react with alkenes to form C(sp3)-C(sp3) bonds. The operationally straightforward reaction exhibits broad functional-group tolerance, facilitates the synthesis of drug-like amines that are not readily accessible by other methods and is amenable to late-stage functionalization applications, making it of interest in areas such as pharmaceutical and agrochemical research.

Selective Palladium(II)-Catalyzed Carbonylation of Methylene ß-C-H Bonds in Aliphatic Amines.

Palladium(II)-catalyzed C-H carbonylation reactions of methylene C-H bonds in secondary aliphatic amines lead to the formation of trans-disubstituted ß-lactams in excellent yields and selectivities. The generality of the C-H carbonylation process is aided by the action of xantphos-based ligands and is important in securing good yields for the ß-lactam products.

The α-tertiary amine motif drives remarkable selectivity for Pd-catalyzed carbonylation of ß-methylene C-H bonds.

The selective C-H carbonylation of methylene bonds in the presence of traditionally more reactive methyl C-H and C(sp2)-H bonds in α-tertiary amines is reported. The exceptional selectivity is driven by the bulky α-tertiary amine motif, which we hypothesise orientates the activating C-H bond proximal to Pd in order to avoid an unfavourable steric clash with a second α-tertiary amine on the Pd centre, promoting preferential cyclopalladation at the methylene position. The reaction tolerates a range of structurally interesting and synthetically versatile functional groups, delivering the corresponding ß-lactam products in good to excellent yields.

Synthesis of cis-C-iodo-N-tosyl-aziridines using diiodomethyllithium: reaction optimization, product scope and stability, and a protocol for selection of stationary phase for chromatography.

The preparation of C-iodo-N-Ts-aziridines with excellent cis-diastereoselectivity has been achieved in high yields by the addition of diiodomethyllithium to N-tosylimines and N-tosylimine-HSO2Tol adducts. This addition-cyclization protocol successfully provided a wide range of cis-iodoaziridines, including the first examples of alkyl-substituted iodoaziridines, with the reaction tolerating both aryl imines and alkyl imines. An ortho-chlorophenyl imine afforded a ß-amino gem-diiodide under the optimized reaction conditions due to a postulated coordinated intermediate preventing cyclization. An effective protocol to assess the stability of the sensitive iodoaziridine functional group to chromatography was also developed. As a result of the judicious choice of stationary phase, the iodoaziridines could be purified by column chromatography; the use of deactivated basic alumina (activity IV) afforded high yield and purity. Rearrangements of electron-rich aryl-iodoaziridines have been promoted, selectively affording either novel α-iodo-N-Ts-imines or α-iodo-aldehydes in high yield.