Synthesis of Benzoisoselenazolones via Rh(III)-Catalyzed Direct Annulative Selenation by Using Elemental Selenium

Assembly of Selenadiazine Scaffolds via Rh(III)-Catalyzed Amidine-Directed Cascade C-H Selenylation/[5 + 1] Annulation with Elemental Selenium

By employing elemental selenium as the selenium source, we have realized the amidine-directed Rh(III)-catalyzed cascade C-H selenylation/[5 + 1] annulation for the direct construction of structurally novel selenadiazine, benzoselenadiazine, and benzoselenazol-3-amine frameworks with specific site selectivity and good functional group tolerance. Besides, the obtained products can serve as fundamental platforms for subsequent chemical transformations, and thus, the feasible SeNEx reaction, SeNEx/Michael addition, and simple conversion of the selenadiazine product into diverse other organoselenium molecules were demonstrated accordingly. Taken together, the developed methodology efficiently expands the chemical space of organoselenium species.

Highly Electrophilic Intermediates in the Bypass Mechanism of Glutathione Peroxidase: Synthesis, Reactivity, and Structures of Selenocysteine-Derived Cyclic Selenenyl Amides

Selenocysteine (Sec)-derived cyclic selenenyl amides, formed by the intramolecular cyclization of Sec selenenic acids (Sec-SeOHs), have been postulated to function as protective forms in the bypass mechanism of glutathione peroxidase (GPx). However, their chemical properties have not been experimentally elucidated in proteins or small-molecule systems. Recently, we reported the first nuclear magnetic resonance observation of Sec-SeOHs and their cyclization to the corresponding cyclic selenenyl amides by using selenopeptide model systems incorporated in a molecular cradle. Herein, we elucidate the structures and reactivities of Sec-derived cyclic selenenyl amides. The crystal structures and reactions toward a cysteine thiol or a 1,3-diketone-type chemical probe indicated the highly electrophilic character of cyclic selenenyl amides. This suggests that they can serve not only as protective forms to suppress the inactivation of Sec-SeOHs in GPx but also as highly electrophilic intermediates in the reactions of selenoproteins.

Introduction of Methyl Group in Substituted Isoselenazolones: Catalytic and Mechanistic Study

Copper-catalyzed direct selenation of substituted 2-bromo-N-phenylbenzamide substrates with elemental selenium powder provided a series of methoxy-substituted isoselenazolones via the C-Se and Se-N bond formations. Phenolic substituted isoselenazolones have been obtained by O-demethylation of the corresponding methoxy-substituted analogues using boron tribromide. Some isoselenazolones have been structurally characterized by X-ray single-crystal analysis. The glutathione peroxidase (GPx)-like antioxidant activity of isoselenazolones has been evaluated both in thiophenol and coupled-reductase assays. All isoselenazolones showed good GPx-like activities in the coupled-reductase assay. The ferric-reducing antioxidant power of phenolic antioxidants has also been evaluated. The best phenolic antioxidants were found to be good ferric-reducing antioxidant power agents. The single electron transfer, hydrogen atom transfer, and proton-coupled electron transfer mechanisms for the antioxidant properties of all catalysts have been supported by density functional theory calculations. The catalytic cycle was proposed for one of the phenolic isoselenazolones involving diselenide, selenenyl sulfide, selenol, and selenenic acid as intermediates using ⁷⁷Se{¹H} NMR spectroscopy.