Three methods are utilized to synthesize a variety of 6,8-di-C-glycosylflavones bearing identical or distinct glycosyl moieties. Some C-glycosylation compounds are found to have better anti-inflammation activities than the parent flavones. Among them, 6,8-di-C-glucosylapigenin (known as vicenin-2) shows inhibition of TNF-alpha expression and NO production with IC(50) values of 6.8 and 5.2 muM, respectively.
7-Oxygenated aporphines 1-6 possessing anti-configurations have previously been reported. In order to explore their bioactivities, a synthesis was established by utilizing a diastereoselective reductive acid-mediated cyclization followed by palladium-catalyzed ortho-arylations. Moderate XPhos precatalyst loading (10 mol %) and short reaction times (30 min) were sufficient to mediate the arylations. Alkaloids 1-5 were successfully prepared, while (-)-artabonatine A was revised to syn-isomer 30. Consequently, (-)-artabonatine E likely also has a syn-configuration (31).
Dendrobium huoshanense is a valued herbal plant used in traditional Chinese medicine. Fractionation of the water-soluble part of D. huoshanense by repeated chromatography culminated in the isolation of four new 6,8-di-C-glycosyl flavones (1-4), in addition to seven known compounds, comprising malic acid, dimethyl malate, N-phenylacetamide, isopentyl butyrate, salicylic acid, shikimic acid, and isoschaftoside. By detailed spectroscopic analysis, the structures of 1-4 were determined to have a core of apigenin bearing pentoside (arabinoside or xyloside) and rhamnosyl-hexoside (glucoside or galactoside) substituents.
(-)-N-Methylguattescidine (3) is an alkaloid recently isolated from Fissistigma latifolium and assigned as a rare example of a 6a-alkyl aporphine. Herein, we report the synthesis of (±)-3 and the des-hydroxyl derivative 4 using our previously reported ortho-phenol arylation methodology mediated by the XPhos precatalyst as a key synthetic step. In addition, substituents on the aryl halide portion of the ortho-phenol arylation substrates significantly influenced the formation of an oxidized side product.
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