Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. We report the synthesis of a well-defined Ni(I) complex, [(CO2Etbpy)NiCl]4 (1). Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a mechanism proceeding through an initial Ni(I) → Ni(III) oxidative addition. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.

Micellar photocatalysis enables divergent C-H arylation and N dealkylation of benzamides via N-acyliminium cations

Micellar photocatalysis has recently opened new avenues to activate strong carbon halide bonds. So far, however, it has mainly explored strongly reducing conditions restricting the available chemical space to radical or anionic reactivity. Here, we demonstrate a radical-polar crossover process involving cationic intermediates, which enables chemodivergent modification of chlorinated benzamide derivatives via either C H arylation or N dealkylation. The catalytic system operates under mild conditions employing methylene blue as a photocatalyst and blue LEDs as the light source. Factors determining the reactivity of substrates and preliminary mechanistic studies are presented.

Hepatocellular Carcinoma Is a Natural Target for Adeno-Associated Virus (AAV) 2 Vectors

Although therapeutic options are gradually improving, the overall prognosis for patients with hepatocellular carcinoma (HCC) is still poor. Gene therapy-based strategies are developed to complement the therapeutic armamentarium, both in early and late-stage disease. For efficient delivery of transgenes with antitumor activity, vectors demonstrating preferred tumor tropism are required. Here, we report on the natural tropism of adeno-associated virus (AAV) serotype 2 vectors for HCC. When applied intravenously in transgenic HCC mouse models, similar amounts of vectors were detected in the liver and liver tumor tissue. In contrast, transduction efficiency, as indicated by the level of transgene product, was moderate in the liver but was elevated up to 19-fold in mouse tumor tissue. Preferred transduction of HCC compared to hepatocytes was confirmed in precision-cut liver slices from human patient samples. Our mechanistic studies revealed that this preference is due to the improved intracellular processing of AAV2 vectors in HCC, resulting, for example, in nearly 4-fold more AAV vector episomes that serve as templates for gene transcription. Given this background, AAV2 vectors ought to be considered to strengthen current—or develop novel—strategies for treating HCC.

Nickel-Catalyzed Reductive Cross-Coupling of Benzylic Sulfonium Salts with Aryl Iodides

A nickel-catalyzed cross-electrophile coupling of benzylic sulfonium salts with aryl iodides has been developed, providing direct access to diarylalkanes from readily available and stable coupling partners. Preliminary mechanistic studies suggest that the C–S bond cleavage proceeds through a single-electron transfer process to generate a benzylic radical.

Head Removal Enhances Planarian Electrotaxis

Sensing electric fields is an ability that certain animal species utilize for communication, hunting, and spatial orientation. Freshwater planarians move toward the cathode in a static electric field (cathodic electrotaxis). First described by Raymond Pearl more than a century ago, planarian electrotaxis has received little attention and the underlying mechanisms and evolutionary significance remain unknown. We developed an apparatus and scoring metrics for automated quantitative and mechanistic studies of planarian behavior upon exposure to a static electric field. Using this automated setup, we characterized electrotaxis in the planarian Dugesia japonica and found that this species responds to voltage instead of to current, in contrast to results from previous studies using other species. Because longer planarians exhibited more robust electrotaxis than shorter planarians, we hypothesized that signals from the head impede cathodic electrotaxis. To test this hypothesis, we took advantage of the regenerative abilities of planarians and compared electrotaxis in head and tail fragments of various lengths. We found that tail and trunk fragments electrotaxed while head fragments did not, regardless of size. However, we could restore cathodic electrotaxis in head fragments via decapitation, demonstrating that the presence of the head impaired cathodic electrotaxis. This result is in stark contrast to other stimulated behaviors such as phototaxis, thermotaxis or chemotaxis, which are weaker or absent in headless fragments. Thus, electrotaxis may be an important ability of headless planarian fragments to support survival prior to head regeneration.

A combined experimental and theoretical study on the reactivity of nitrenes and nitrene radical anions

Nitrene transfer reactions represent one of the key reactions to rapidly construct new carbon-nitrogen bonds and typically require transition metal catalysts to control the reactivity of the pivotal nitrene intermediate. Herein, we report on the application of iminoiodinanes in amination reactions under visible light photochemical conditions. While a triplet nitrene can be accessed under catalyst-free conditions, the use of a suitable photosensitizer allows the access of a nitrene radical anion. Computational and mechanistic studies rationalize the access and reactivity of triplet nitrene and nitrene radical anion and allow the direct comparison of both amination reagents. We conclude with applications of both reagents in organic synthesis and showcase their reactivity in the reaction with olefins, which underline their markedly distinct reactivity. Both reagents can be accessed under mild reaction conditions at room temperature without the necessity to exclude moisture or air, which renders these metal-free, photochemical amination reactions highly practical.

Halogen-bonding-promoted Photo-induced C–X Borylation of Aryl Halide using Phenol Derivatives

This study investigates the photo-induced C–X borylation reaction of aryl halides by forming a halogen-bonding complex. The method employs 2-naphthol as a halogen-bonding acceptor and proceeds under mild conditions without a photoredox catalyst under 420 nm blue light irradiation. The method is highly chemoselective, broadly functional group tolerant, and provides concise access to corresponding boronate esters. Mechanistic studies reveal that forming the halogen-bonding complex between aryl halide and naphthol acts as an electron donor-acceptor complex to furnish aryl radicals through photo-induced electron transfer.