Synthesis, conformational analysis, and the glycosidic coupling reaction of substituted 2,7-dioxabicyclo[4.1.0]heptanes: 1,2-anhydro-3,4-di-O-benzyl-β-l- and β-d-rhamnopyranoses
作者:Qian Chen、Fanzuo Kong、Lingxiao Cao
DOI:10.1016/0008-6215(93)84176-7
日期:1993.2
were obtained in high yields. Conformational calculations, which were carried out using vicinal proton-proton coupling constants by the modified Karplus equation, suggested that the conformations of the pyranose rings of the title compounds were basically a half chair (4H5) with some flattening at C-4. Force-field calculations (MMP2) confirmed the experimental conformation with good agreement. The coupling
由L-鼠李糖合成1,2-脱水-3,4-二-O-苄基-α-鼠李吡喃糖,而D-对映异构体由甲基6-脱氧-2,3-O-异亚丙基-α合成-D-甘露吡喃糖苷。对于这两种合成,关键中间体是2-O-乙酰基-3,4-二-O-苄基-α-D-和-α-L-鼠李糖基吡喃糖基氯,它们是通过氯化从相应的二乙酸酯定量制备的。用叔丁醇钾在氧戊烷中容易地完成氯化物的闭环反应,并以高收率获得了结晶的1,2-脱水-3,4-二-O-苄基-β-D-和β-L-鼠李吡喃糖。 。通过改进的Karplus方程使用邻近质子-质子耦合常数进行的构象计算,这表明标题化合物的吡喃糖环的构象基本上是半椅(4H5),在C-4处有些展平。力场计算(MMP2)证实了实验构象,吻合得很好。1,2-脱水-L-鼠李糖醚与1,2; 3,4-二-O-异亚丙基-α-D-吡喃半乳糖的偶联反应是通过路易斯酸催化在环氧丙烷中进行的,只有α获得了连接的二糖。