Stortz Carlos A
Departamento de Química Orgánica-CIHIDECAR, Facultad de Ciencias Exactas y Naturales, UBA, Pab 2 Ciudad Universitaria, 1428 Buenos Aires, Argentina.
Carbohydr Res. 2002 Nov 19;337(21-23):2311-23. doi: 10.1016/s0008-6215(02)00173-8.
The adiabatic conformational surfaces of several beta-linked disaccharides, which correspond to the repeating structures of carrageenans, were calculated using the MM3 force-field. The studies were carried out on the disaccharide beta-D-Galp-(1 --> 4)-alpha-D-Galp and eight sulfated derivatives, as well as on carrabiose (beta-D-Galp-(1 --> 4)-3,6-An-alpha-D-Galp) and five sulfated derivatives. The presence of 3,6-anhydrogalactose does not change the main features of the maps, although it increases the flexibility of the glycosidic linkage. Sulfation neither produces a striking effect on the map shape, nor a shift on the global minimum, which always remains with psi (theta(C-1'-O-4-C-4C-5)) in trans orientation, and phi (theta(O-5'-C-1'-O-4-C-4)) with a value close to -80 degrees. This effect differs from that occurring on the alpha linkage of equivalent disaccharides, for which the sulfation pattern on the beta-galactose unit shifts the global minima to different positions. A reduction in the flexibility (originated in a deepening of the global minimum well) is observed by sulfation on position 2 of the beta-D-galactose unit, and by sulfation of position 6 of the alpha-D-galactose unit (when the beta-D-galactose unit is 4-sulfated). Within the compounds containing 3,6-anhydrogalactose, the effect of sulfation is even less noticeable. The calculated low-energy regions on carrabiose derivatives agree with X-ray diffraction data on carrageenan fibers and on peracetylated carrabiose dimethyl acetal, and with NOE calculations carried out on kappa-carrabiose.
使用MM3力场计算了几种与角叉菜胶重复结构相对应的β-连接二糖的绝热构象表面。研究对象为二糖β-D-吡喃半乳糖-(1→4)-α-D-吡喃半乳糖及其八种硫酸化衍生物，以及卡拉比糖（β-D-吡喃半乳糖-(1→4)-3,6-脱水-α-D-吡喃半乳糖）及其五种硫酸化衍生物。3,6-脱水半乳糖的存在虽增加了糖苷键的灵活性，但并未改变图谱的主要特征。硫酸化既未对图谱形状产生显著影响，也未使全局最小值发生偏移，全局最小值处的ψ（θ(C-1'-O-4-C-4C-5)）始终处于反式构象，φ（θ(O-5'-C-1'-O-4-C-4)）的值接近-80°。这种效应与等效二糖α-连接上的情况不同，在β-半乳糖单元上的硫酸化模式会使等效二糖的全局最小值移至不同位置。通过对β-D-吡喃半乳糖单元的2位进行硫酸化，以及对α-D-吡喃半乳糖单元的6位进行硫酸化（当β-D-吡喃半乳糖单元为4-硫酸化时），可观察到灵活性降低（源于全局最小值阱的加深）。在含有3,6-脱水半乳糖的化合物中，硫酸化的影响甚至更不明显。卡拉比糖衍生物上计算出的低能区域与角叉菜胶纤维和全乙酰化卡拉比糖二甲基缩醛的X射线衍射数据以及对κ-卡拉比糖进行的NOE计算结果相符。
