Study for stereoselective synthesis of oligosaccharides by new glycosylation methods

在四（五氟苯基）硼酸的催化作用下，糖基受体与α-甘露糖基6-硝基-2-苯并噻唑酸供体的高选择性甘露糖基化反应顺利进行，得到相应的高收率双糖。用原位形成的糖基供体——苯基保护的糖基甲基二苯基碘化磷，对几种糖基受体进行了温和的、高选择性的糖基化反应，在室温下，在CH2Cl2中高产出相应的α-二糖，而不需要任何酸启动子的帮助。F1a抗原是肿瘤相关的o -粘蛋白糖基氨基酸的一个成员，我们尝试通过一锅顺序糖基化来聚合全合成F1a抗原。采用三氟甲磺酸三甲酯与n -碘丁二酰亚胺相结合的方法，成功地进行了氨基酸与巯基糖苷的高选择性糖基化反应，获得了高收率的糖基氨基酸。其次，通过促进三烷基四（五氟苯）硼酸盐或三氟甲烷磺酸，尝试了巯基糖苷与半乳糖基碳酸苯或氟的糖基化；进一步添加糖基氨基酸和NIS，保护F1a的总产量分别为80%和89%。去除保护基团后，得到了高收率所需的三糖。

Highly p-selective mannnosylations of glycosyl acceptors with an α-mannosyl 6-nitro-2-benzothiazoate donor were carried out smoothly in the presence of a catalytic amount of tetrakis(pentafluorophenyl)boric acid to afford the corresponding disaccharides in good to high yields.A mild and highly a-selective glycosylation of several glycosyl acceptors was performed with an in situ formed glycosyl donor, benzyl-protected glycosyl methyldiphenylphosphonium iodide, to afford the corresponding α-disaccharides in high yields in CH2Cl2 at room temperature without any assistance of acid promoters.A convergent total synthesis of F1a antigen, a member of the tumor-associated O-linked mucin glycosyl amino acid, was tried by one-pot sequential glycosylation. Highly a-selective glycosylation of amino acid with thioglycoside was successfully carried out by combining trityl trifluoromethanesulfonate and N-iodosuccinimide which gave glycosyl amino acid in high yield. Next, the glycosylation of thioglycoside with galactosyl phenyl carbonate or fluoride was tried by the promotion of trityl tetrakis(pentafluorophenyl)borate or trifluoromethanesulfonic acid ; protected F1a was afforded in 80 or 89% overall yield, respectively, by the further addition of glycosyl aminoacid and NIS. The desired trisaccharide was obtained in high yield after removal of the protecting groups.