CIHIDECAR, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina.
Carbohydr Res. 2011 Dec 27;346(18):2838-48. doi: 10.1016/j.carres.2011.10.004. Epub 2011 Oct 12.
Conformationally restricted 3,5-O-di-tert-butylsilylene-D-galactofuranosyl trichloroacetimidate donors were synthesized from allyl α-D-galactofuranoside for the construction of 1,2-cis α-D-galactofuranosyl linkages. Glycosylation reactions were performed with several acceptors, including D-galactono-1,4-lactone, D-rhamnopyranosyl, and D-mannopyranosyl derivatives. The influence of the temperature and the reaction solvents was evaluated, as well as the 6-O-substitution pattern of the donor. The higher α-selectivities were obtained at -78 °C in diethyl ether as solvent. 6-O-Acetyl substitution on constrained donor increased the α-selectivity compared to the 6-O-benzyl substitution. Almost no selectivities were observed in the non-participating solvent CH(2)Cl(2). In contrast, ethereal solvents enhanced the α-selectivity suggesting a participating effect in the reaction intermediate.
为了构建 1,2-顺式α-D-半乳糖苷键，我们合成了具有构象限制的 3,5-O-二叔丁基硅亚基-D-半乳糖呋喃糖基三氯乙酰亚胺供体，从烯丙基α-D-半乳糖呋喃糖苷开始。与几种受体（包括 D-半乳糖-1,4-内酯、D-鼠李吡喃糖苷和 D-甘露吡喃糖苷衍生物）进行了糖苷化反应。评估了温度和反应溶剂的影响，以及供体的 6-O-取代模式。在二乙醚溶剂中，在-78°C 下获得了更高的α选择性。与 6-O-苄基取代相比，受约束供体上的 6-O-乙酰基取代增加了α选择性。在非参与性溶剂 CH(2)Cl(2)中几乎没有观察到选择性。相比之下，醚类溶剂提高了α选择性，表明反应中间体存在参与效应。
