The tetra-O-methyl ether of quercetin (QU) 3 (54%), 3,7,4′-tri-O-methyl ether 4 (30%), and a previously unreported 3,7,3-tri-O-methyl ether of QU 5 (7%) were obtained via methylation of QU by an excess of diazomethane in dioxane. Their structures were established using 2D NMR (¹H–¹H COSY, ¹H–¹H NOESY, ¹H–¹³C HSQC, ¹H–¹³C HMBC). Tetra-O-methyl ether of QU 3 exhibited pronounced hypoglycemic activity, reduced alloxan-induced hyperglycemia in rats by 44.5% compared to a control, and was 2.7 times more active than QU.

中文翻译：

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重氮甲烷对槲皮素的甲基化作用及其四-O-甲基醚的降血糖活性

槲皮素（QU）3（54％），3,7,4'-三-O-甲基醚4（30％）和以前未报道的3,7,3-tri- O的四-O-甲基醚通过用过量的重氮甲烷在二恶烷中使QU甲基化，获得QU 5的-甲基醚（7％）。它们的结构使用2D NMR（¹ H– ¹ H COSY，¹ H– ¹ H NOESY，¹ H– ¹³ C HSQC，¹ H– ¹³ C HMBC）建立。四ø -甲基QU的醚3 具有明显的降血糖活性，与对照相比，大鼠的四氧嘧啶诱导的高血糖症减少了44.5％，活性是QU的2.7倍。