Bonas G, Vignon M R, Pérez S
Centre de Recherches sur les Macromolécules Végétales, C.N.R.S., Grenoble, France.
Carbohydr Res. 1991 Apr 24;211(2):191-205. doi: 10.1016/0008-6215(91)80091-z.
The conformational properties of a cyclic trisaccharide: [O-beta-D-glucopyranosyl-(1----6)]3 1,6"-anhydride nonacetate (C36H48O24, 1) have been established by high-resolution 1H- and 13C-n.m.r. spectroscopy in conjunction with potential-energy and molecular-mechanics calculations. The n.m.r. parameters used were nuclear Overhauser enhancements (n.O.e.) and coupling constants. From theoretical models of the trisaccharide, a statistical-mechanics approach was used to compute an ensemble average-relaxation matrix from which the n.O.e. were calculated. The observed nuclear Overhauser enhancements as measured by n.m.r. spectroscopy may be satisfactorily modelled if averaging over two conformational states is considered. In solution, both conformations of the molecule exhibit three-fold symmetry; the beta-linked glucopyranose rings have the 4C1 conformation. In one conformer, the orientation about the (1----6) linkage is characterized by torsion angles phi = 79.5 degrees, psi = 143.5, and omega = -64.3. For the other conformer, these values are phi = -137.7, psi = 68.2, and omega = 45.6. The existence of such a conformer shows that solution behaviour is not dominated by the stabilizing influence of the exoanomeric effect.
[O-β-D-吡喃葡萄糖基-(1→6)]3 1,6''-酐非乙酸酯（C36H48O24, 1）的构象性质已通过高分辨率1H和13C核磁共振光谱结合势能和分子力学计算得以确定。所使用的核磁共振参数为核Overhauser增强效应（n.O.e.）和耦合常数。从三糖的理论模型出发，采用统计力学方法计算了一个系综平均弛豫矩阵，并据此计算了n.O.e.。如果考虑对两种构象状态进行平均，那么通过核磁共振光谱测量得到的观测核Overhauser增强效应就能得到令人满意的模拟。在溶液中，该分子的两种构象均呈现三重对称性；β-连接的吡喃葡萄糖环具有4C1构象。在一种构象异构体中，(1→6)键的取向由扭转角φ = 79.5°、ψ = 143.5°和ω = -64.3°表征。对于另一种构象异构体，这些值分别为φ = -137.7°、ψ = 68.2°和ω = 45.6°。这种构象异构体的存在表明，溶液行为并非由端基异构效应的稳定作用主导。
