Synthesis, NMR spectroscopy and conformational studies of the four anomeric methyl glycosides of the trisaccharide D-Glcp-(1→3)-[D-Glcp-(1→4)]-α-D-Glcp
作者:Peter Söderman、Per-Erik Jansson、Göran Widmalm
DOI:10.1039/a707346a
日期:——
The four anomeric methyl glycosides of the vicinally disubstituted trisaccharide D-Glcp-(1â3)-[D-Glcp-(1â4)]-α-D-Glcp have been synthesized using silver trifluoromethanesulfonate mediated glycosylations. The 1H and 13C NMR resonances have been assigned and used for extraction of glycosylation shifts, i.e. the differences between chemical shifts for signals from the trisaccharides and those of the respective monomers, as well as those derived by addition of the glycosylation shifts for each disaccharide element. Glycosylation shifts are up to 0.5 ppm for proton and 10 ppm for carbon. Deviations from additivity are â0.2â0.1 ppm for proton and â4.5â2.3 ppm for carbon, usually confined to the atoms at the linkage positions. The conformational space spanned for the trisaccharides, and the constituent disaccharides, has been investigated by Metropolis Monte Carlo simulations using the HSEA force field. The α-linked glucosyl groups show larger conformational changes with multiple energy minima, whereas the β-linked glucosyl groups have a single energy minimum, close to that identified for the constituent disaccharide.
四种脱氧间位二取代的三糖D-Glcp-(1→3)-[D-Glcp-(1→4)]-α-D-Glcp的异构体甲基糖苷已通过三氟甲磺酸银催化的糖苷化反应合成。已对其1H和13C NMR谱峰进行了赋值,并用于提取糖苷化位移,即三糖信号与各自单体信号的化学位移之间的差异,以及对每个二糖单元的糖苷化位移的累加。糖苷化位移的变化范围为质子最多可达0.5 ppm,碳可达10 ppm。偏离加性规律的值则为-0.2至-0.1 ppm(质子)和-4.5至-2.3 ppm(碳),通常集中在连接位置的原子上。通过使用HSEA力场的Metropolis Monte Carlo模拟,研究了三糖及其组成的二糖所涵盖的构象空间。α-链接的葡萄糖基显示出较大的构象变化和多个能量最小点,而β-链接的葡萄糖基则只有一个能量最小点,接近于其组成的二糖所识别的能量最低点。