The rotational preferences of the hydroxymethyl group in pyranosides is known to depend on the local environment, whether in solid, solution, or gas phase. By combining molecular dynamics (MD) simulations with NMR spectroscopy the rotational preferences for the ω angle in methyl 2,3-di-O-methyl-α-D-glucopyranoside (3) and methyl 2,3-di-O-methyl-α-D-galactopyranoside (6) in a variety of solvents, with polarities ranging from 80 to 2.3 D have been determined. The effects of solvent polarity on intramolecular hydrogen bonding have been identified and quantified. In water, the internal hydrogen bonding networks are disrupted by competition with hydrogen bonds to the solvent. When the internal hydrogen bonds are differentially disrupted, the rotamer populations associated with the ω angle may be altered. In the case of 3 in water, the preferential disruption of the interaction between HO6 and O4 destabilizes the tg rotamer, leading to the observed preference for gauche rotamers. Without the hydrogen bond enhancement offered by a low polarity environment, both 3 and 6 display rotamer populations that are consistent with expectations based on the minimization of repulsive intramolecular oxygenoxygen interactions. In a low polarity environment, HO6 prefers to interact with O4, however, in water these interactions are markedly weakened, indicating that HO6 acts as a hydrogen bond donor to water.Key words: carbohydrate, rotamer, molecular dynamics simulation, MD, NMR.
众所周知,吡喃糖苷中羟甲基的旋转偏好取决于固相、溶液相或气相的局部环境。通过将分子动力学(MD)模拟与核磁共振光谱相结合,确定了甲基 2,3-二-O-甲基-α-D-吡喃葡萄糖苷(3)和甲基 2,3-二-O-甲基-α-D-吡喃半乳糖苷(6)在极性为 80 到 2.3 D 的各种溶剂中的ω角旋转偏好。确定并量化了溶剂极性对分子内氢键的影响。在水中,内部氢键网络因与溶剂氢键的竞争而被破坏。当内部氢键受到不同程度的破坏时,与 ω 角相关的转子群可能会发生变化。就 3 在水中的情况而言,HO6 和 O4 之间相互作用的优先破坏会破坏 tg 转子的稳定性,从而导致观察到的偏好高切转子。如果没有低极性环境提供的氢键增强作用,3 和 6 显示的转子群与基于分子内氧氧排斥性相互作用最小化的预期一致。在低极性环境中,HO6 更喜欢与 O4 相互作用,但在水中,这些相互作用明显减弱,这表明 HO6 是水的氢键供体。