The quantitative analysis of reaction products showed that the reaction of 6A,6D-di-O-trityl-α-cyclodextrin (CD), AD-isomer, with trityl chloride in pyridine at 55 °C gave 6A,6B,6E-tri-O-trityl-α-CD, the amount of which was only 25% of that of simultaneously formed 6A,6B,6D-tri-O-trityl-α-CD. This indicates that the bulky trityl groups of glucopyranose-A and -D (Glu-A and -D, respectively) in the AD-isomer mainly retard the additional tritylation of the C(6)-OH of the adjacent glucopyranoses in a counter-clockwise direction (Glu-F and -C, respectively). 1H NMR spectra of the AD-isomer showed that the O(6)-H and C(6)-H signals of Glu-C and -F are shifted upfield due to the ring current of the trityl groups. Thus, it is concluded that the bulky trityl groups on Glu-A and Glu-D are oriented to Glu-F and Glu-C, respectively, and sterically retard additional tritylation on Glu-F and Glu-C. Similar steric hindrance was also observed in the additional tritylations of mono-6-O-trityl-α-CD, 6A,6B-di- and 6A,6C-di-O-trityl-α-CD’s.
反应产物的定量分析表明,在55℃的
吡啶中,6A,6D-双O-三苯基甲基-α-
环糊精(CD),AD异构体,与三苯基
氯化物反应,生成了仅为同时生成的6A,6B,6D-三O-三苯基甲基-α-CD的25%的6A,6B,6E-三O-三苯基甲基-α-CD。这表明AD异构体中
葡萄糖吡喃-A和-D(Glu-A和-D)的笨重三苯基甲基基团主要在逆时针方向(分别为Glu-F和-C)上阻碍相邻
葡萄糖吡喃的C(6)-OH的附加三苯基化反应。AD异构体的1H NMR光谱表明,由于三苯基甲基基团的环电流,Glu-C和-F的O(6)-H和C(6)-H信号向上移动。因此,可以得出结论,Glu-A和Glu-D上的笨重三苯基甲基基团定向到Glu-F和Glu-C,分别在Glu-F和Glu-C上立体阻碍了附加的三苯基化反应。在单6-O-三苯基甲基-α-CD、6A,6B-双和6A,6C-双O-三苯基甲基-α-CD的附加三苯基化反应中也观察到类似的立体位阻。