- NHC-Catalyzed Dual Stetter Reaction: A Mild Cascade Annulation for the Syntheses of Naphthoquinones, Isoflavanones, and Sugar-Based Chiral Analogues
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The N-heterocycle carbene (NHC)-catalyzed dual Stetter cascade reaction is discovered through coupling of β-nitrostyrene with phthalaldehyde under mild conditions to furnish valuable aryl-naphthoquinones. The generality of the new reaction is validated through the development of a C-C and O-C bond forming Stetter cascade reaction using salicylaldehydes to obtain functionalized dihydroisoflavanones. The mild NHC organocatalysis is successfully employed for the construction of optically pure sugar-based naphthoquinones and dihydroisoflavanones. Herein, NHC is found as a unique and powerful organocatalyst to construct homoatomic C-C cross-coupling, heteroatomic O-C bond formation, and cascade cyclization utilizing NO2 as a leaving group at ambient temperature. A mechanistic pathway of the new metal-free catalysis is predicted on the basis of our ESI-MS study of the ongoing reaction and literature.
- Mitra, Rajendra N.,Show, Krishanu,Barman, Debabrata,Sarkar, Satinath,Maiti, Dilip K.
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- Exploiting Alkylquinone Tautomerization: Amine Benzylation
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A general protocol for the synthesis of benzylic amines via side-chain amination of alkylquinones is reported. The reactions are initiated by the tautomerization of an alkylquinone to the corresponding quinone methide, which is subsequently trapped in situ by an amine nucleophile. This process is promoted by tertiary amines in protic solvents under mild conditions and is compatible with many functional groups. 1,2- and 1,4-benzoquinones, as well as naphthoquinones, participate in this reaction using a wide range of primary and secondary amines/anilines. The synthetic utility of this transformation is also explored.
- Mori-Quiroz, Luis M.,Clift, Michael D.
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- Enantioselective Epoxidation of 2,3-Disubstituted Naphthoquinones by a Side Chain Truncated Guanidine-Urea Bifunctional Organocatalyst
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An organocatalytic enantioselective epoxidation of 2,3-disubstituted naphthoquinones with tert-butyl hydroperoxide as an oxidant was developed using a guanidine-urea bifunctional catalyst lacking C2 symmetry, which was designed based upon the insights obtained from the DFT calculation model for our previous C2 symmetric catalyst. The present organocatalytic reaction provides access to a variety of optically active naphthoquinone epoxides bearing aryl and methyl substituents at C2 and C3 in high yields with high enantioselectivities (up to 97:3 er).
- Orihara, Tatsuya,Kawaguchi, Masaki,Hosoya, Keisuke,Tsutsumi, Ryosuke,Yamanaka, Masahiro,Odagi, Minami,Nagasawa, Kazuo
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p. 15232 - 15240
(2020/12/02)
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- Comprehensive evaluation of antioxidant effects of Japanese Kampo medicines led to identification of Tsudosan formulation as a potent antioxidant agent
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Oxidative stress due to the overproduction of reactive oxygen species plays an important role in the pathogenesis of various diseases. In the present study, we comprehensively evaluated the antioxidant activities of 147 oral formulations of Japanese traditional herbal medicines (Kampo medicines), representing the entire panel of oral Kampo medicines listed in the Japanese National Health Insurance Drug List, using in vitro radical scavenging assays, including the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity assay, the superoxide anion scavenging activity assay, and the oxygen radical absorption capacity assay. Three of the formulations tested, namely, Tsudosan, Daisaikoto, and Masiningan, showed the most potent in vitro antioxidant activities and were selected for further investigation of their intracellular and in vivo antioxidant effects. The results of the 2′,7′-dichlorodihydrofluorescin diacetate assay demonstrated that all three Kampo medicines significantly inhibited hydrogen peroxide-induced oxidative stress in human hepatocellular liver carcinoma HepG2 cells. In addition, Tsudosan significantly increased the serum biological antioxidant potential values when orally administrated to mice, indicating that it also had in vivo antioxidant activity. The potent antioxidant activity of Tsudosan may be one of the mechanisms closely correlated to its clinical usage against blood stasis.
- Sato, Naoko,Li, Wei,Takemoto, Hiroaki,Takeuchi, Mio,Nakamura, Ai,Tokura, Emi,Akahane, Chie,Ueno, Kanako,Komatsu, Kana,Kuriyama, Noriko,Onoda, Toshihisa,Higai, Koji,Koike, Kazuo
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p. 163 - 172
(2018/11/06)
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