We report a redox-neutral method for nucleophilic fluorination of N-hydroxyphthalimide esters using an Ir photocatalyst under visible light irradiation. The method provides access to a broad range of ...aliphatic fluorides, including primary, secondary, and tertiary benzylic fluorides as well as unactivated tertiary fluorides, that are typically inaccessible by nucleophilic fluorination due to competing elimination. In addition, we show that the decarboxylative fluorination conditions are readily adapted to radiofluorination with 18FKF. We propose that the reactions proceed by two electron transfers between the Ir catalyst and redox-active ester substrate to afford a carbocation intermediate that undergoes subsequent trapping by fluoride. Examples of trapping with O- and C-centered nucleophiles and deoxyfluorination via N-hydroxyphthalimidoyl oxalates are also presented, suggesting that this approach may offer a general blueprint for affecting redox-neutral SN1 substitutions under mild conditions.
The advent of antibody-drug conjugates as pharmaceuticals has fuelled a need for reliable methods of site-selective protein modification that furnish homogeneous adducts. Although bioorthogonal ...methods that use engineered amino acids often provide an elegant solution to the question of selective functionalization, achieving homogeneity using native amino acids remains a challenge. Here, we explore visible-light-mediated single-electron transfer as a mechanism towards enabling site- and chemoselective bioconjugation. Specifically, we demonstrate the use of photoredox catalysis as a platform to selectivity wherein the discrepancy in oxidation potentials between internal versus C-terminal carboxylates can be exploited towards obtaining C-terminal functionalization exclusively. This oxidation potential-gated technology is amenable to endogenous peptides and has been successfully demonstrated on the protein insulin. As a fundamentally new approach to bioconjugation this methodology provides a blueprint toward the development of photoredox catalysis as a generic platform to target other redox-active side chains for native conjugation.
We report here a catalytic method for the modular ring expansion of cyclic aliphatic alcohols. In this work, proton-coupled electron transfer activation of an allylic alcohol substrate affords an ...alkoxy radical intermediate that undergoes subsequent C–C bond cleavage to furnish an enone and a tethered alkyl radical. Recombination of this alkyl radical with the revealed olefin acceptor in turn produces a ring-expanded ketone product. The regioselectivity of this C–C bond-forming event can be reliably controlled via substituents on the olefin substrate, providing a means to convert a simple N-membered ring substrate to either n+1 or n+2 ring adducts in a selective fashion.
Bioconjugation technologies have revolutionized the practice of biology and medicine by allowing access to novel biomolecular scaffolds. New methods for residue-selective bioconjugation are highly ...sought to expand the toolbox for a variety of bioconjugation applications. Herein we report a site-selective methionine bioconjugation protocol that uses photoexcited lumiflavin to generate open-shell intermediates. This reduction-potential-gated strategy enables access to residues unavailable with traditional nucleophilicity-based conjugation methods. To demonstrate the versatility and robustness of this new protocol, we have modified various proteins and further utilized this functional handle to append diverse biological payloads.
Controlling site selectivity of C–H activation without using a directing group remains a significant challenge. While Pd(II) catalysts modulated by a mutually repulsive pyridine-type ligand have ...been shown to favor the relatively electron-rich carbon centers of arenes, reversing the selectivity to favor palladation at the relatively electron-deficient positions has not been possible. Herein we report the first catalytic system that effectively performs meta C–H arylation of a variety of alkoxy aromatics including 2,3-dihydrobenzofuran and chromane with exclusive meta site selectivity, thus reversing the conventional site selectivity governed by native electronic effects. The identification of an effective ligand and modified norbornene (NBE-CO2Me), as well as taking advantage of the statistics, are essential for achieving the exclusive meta selectivity.
Pd-catalyzed C(sp3)–H activation of alcohol typically shows β-selectivity due to the required distance between the chelating atom in the attached directing group and the targeted C–H bonds. Herein ...we report the design of a hemilabile directing group which exploits the chelation of a readily removable benzyl ether moiety to direct γ- or δ-C–H carbonylation and olefination of alcohols. The utility of this approach is also demonstrated in the late-stage C–H functionalization of β-estradiol to rapidly prepare desired analogues that required multi-step syntheses with classical methods.
AbstactThe growing prevalence of synthetically modified proteins in pharmaceuticals and materials has exposed the need for efficient strategies to enable chemical modifications with high ...site-selectivity. While genetic engineering can incorporate non-natural amino acids into recombinant proteins, regioselective chemical modification of wild-type proteins remains a challenge. Herein, we use photoredox catalysis to develop a site-selective tyrosine bioconjugation pathway that incorporates bioorthogonal formyl groups, which subsequently allows for the synthesis of structurally defined fluorescent conjugates from native proteins. A water-soluble photocatalyst, lumiflavin, has been shown to induce oxidative coupling between a previously unreported phenoxazine dialdehyde tag and a single tyrosine site, even in the presence of multiple tyrosyl side chains, through the formation of a covalent C–N bond. A variety of native proteins, including those with multiple tyrosines, can successfully undergo both tyrosine-specific and single-site-selective labelling. This technology directly introduces aldehyde moieties onto native proteins, enabling rapid product diversification using an array of well-established bioorthogonal functionalization protocols including the alkyne–azide click reaction.Regioselective chemical modification of wild-type proteins remains challenging. Now, by harnessing the varied SOMOphilicity of native tyrosine residues through photoredox catalysis, a site-selective bioconjugation method has been developed. This technology directly incorporates bioorthogonal formyl groups in one step, forming structurally defined fluorescent conjugates that can be rapidly diversified to biorelevant products.
L,X-Type transient directing groups (TDGs) based on a reversible imine linkage have emerged as broadly useful tools for C–H activation of ketones and free amines. However, competitive binding ...interactions among multiple reaction components (TDG itself, substrate, and substrate–TDG adduct) with the palladium catalyst often lead to the formation of multiple unreactive complexes, rendering ligand development extremely challenging. Herein, we report the finding of versatile 2-pyridone ligands that addresses these problems and significantly improves the γ-methylene arylation of alkyl amines, extending the coupling partners to a wide range of medicinally important heteroaryl iodides and even previously unreactive heteroaryl bromides. The combination of an appropriate transient directing group and pyridone ligand has also enabled the δ-arylation of alkyl amines. Notably, our transient directing group design reveals the importance of matching the size of the Pd-chelation with different transient directing groups and the size of palladacycles generated from γ- and δ-C–H bonds: TDGs that coordinate with Pd(II) to form a six-membered chelate are selective toward γ-C–H bonds, whereas TDGs that coordinate with Pd(II) via a five-membered chelate tend to activate δ-C–H bonds. These findings provide an avenue for developing protecting group free and selective C–H functionalization using the transient directing group strategy.
Fluorine is known to promote ortho‐C−H metalation. Based upon this reactivity, we employed an activated norbornene that traps the ortho‐palladation intermediate and is then relayed to the meta ...position, leading to meta‐selective C−H arylation of fluoroarenes. Deuterium experiment suggests that this meta‐arylation is initiated by ortho C−H activation and the catalytic cycle is terminated by C‐2 protonation. A dual‐ligand system is crucial for the observed high reactivity and site selectivity. Applying this approach to simple benzene or other arenes also affords arylation products with good yield and site selectivity.
meta‐Selective C−H arylation: An activated norbornene traps the ortho‐palladation intermediate in the ortho‐C−H metalation of fluoroarenes and is then relayed to the meta position, leading to meta‐selective C−H arylation. A dual‐ligand system is crucial for the observed high reactivity and selectivity. Applying this approach to simple benzene or other arenes also affords arylation products with good yields and site selectivity.
Background
Milvexian (BMS‐986177/JNJ‐70033093) is an orally bioavailable factor XIa (FXIa) inhibitor currently in phase 2 clinical trials.
Objectives
To evaluate in vitro properties and in vivo ...characteristics of milvexian.
Methods
In vitro properties of milvexian were evaluated with coagulation and enzyme assays, and in vivo profiles were characterized with rabbit models of electrolytic‐induced carotid arterial thrombosis and cuticle bleeding time (BT).
Results
Milvexian is an active‐site, reversible inhibitor of human and rabbit FXIa (Ki 0.11 and 0.38 nM, respectively). Milvexian increased activated partial thromboplastin time (APTT) without changing prothrombin time and potently prolonged plasma APTT in humans and rabbits. Milvexian did not alter platelet aggregation to ADP, arachidonic acid, or collagen. Milvexian was evaluated for in vivo prevention and treatment of thrombosis. For prevention, milvexian 0.063 + 0.04, 0.25 + 0.17, and 1 + 0.67 mg/kg+mg/kg/h preserved 32 ± 6*, 54 ± 10*, and 76 ± 5%* of carotid blood flow (CBF) and reduced thrombus weight by 15 ± 10*, 45 ± 2*, and 70 ± 4%*, respectively (*p < .05; n = 6/dose). For treatment, thrombosis was initiated for 15 min and CBF decreased to 40% of control. Seventy‐five minutes after milvexian administration, CBF averaged 1 ± 0.3, 39 ± 10, and 66 ± 2%* in groups treated with vehicle and milvexian 0.25 + 0.17 and 1 + 0.67 mg/kg+mg/kg/h, respectively (*p < .05 vs. vehicle; n = 6/group). The combination of milvexian 1 + 0.67 mg/kg+mg/kg/h and aspirin 4 mg/kg/h intravenous did not increase BT versus aspirin monotherapy.
Conclusions
Milvexian is an effective antithrombotic agent with limited impact on hemostasis, even when combined with aspirin in rabbits. This study supports inhibition of FXIa with milvexian as a promising antithrombotic therapy with a wide therapeutic window.
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