A systematic study is presented of the efficiency of the most common glycosylation methods using standard 2-deoxy-2-phthalimidogalactopyranosyl donors ethyl 4-O-acetyl-3,6-di-O- benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (3a), 4-O-Acetyl-3,6-di-O-benzyl- 2-deoxy-2-phthalimido-β-D-galactopyranosyl bromide (4), 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl fluoride (5b), O-(4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl) trichloroacetimidate (7) and ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (8), pent-4-enyl 3,6-di-O-benzyl- and 3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranoside (10a) and (10b) and pent-4-enyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-4-O-(trimethylsilyl)-β-D-galactopyranoside (11) as glycosyl acceptors in the synthesis of 2-amino-2-deoxy-β-D-galactopyranosyl-(1→4)-2-amino-2-deoxy-β-D-galactopyranosides 12, 16a and 17a. It was found that due to a low reactivity of the axial OH(4) group of glycosyl acceptors, disaccharides 16b and 17b with α(1→4) bond were also formed. The unexpected intermolecular migration of ethylsufanyl group from the reducing end of glycosyl acceptor 8 the reducing end of the activated form of glycosyl donor 4 in the glycosylation step to give ethylsulfanyl derivative 3a was proved. For preparation of the glycosyl donors and glycosyl acceptors with galacto configuration an approach based on epimerization of 4-O-mesyl derivatives of appropriate synthons with gluco configuration 2a and 2b was employed.
本文对使用标准2-去
氧-2-邻
苯二甲
酰胺基半
乳糖供体乙基4-
O-
乙酰基-3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-1-
硫代-β-
D-半乳糖苷(
3a)、4-
O-
乙酰基-3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-β-
D-半乳糖苷
溴化物(
4)、4-
O-
乙酰基-3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-β-
D-半乳糖苷
氟化物(
5b)、
O-(4-
O-
乙酰基-3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-β-
D-半乳糖苷)三
氯乙
酰胺盐(
7)和乙基3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-1-
硫代-β-
D-半乳糖苷(
8)、戊-4-
烯基3,6-双-
O-
苄基和3-
O-
烯基-6-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-β-
D-半乳糖苷(
10a)和(
10b)以及戊-4-
烯基3,6-双-
O-
苄基-2-去
氧-2-邻
苯二甲
酰胺基-4-
O-(三
甲基硅基)-β-
D-半乳糖苷(
11)作为糖基受体,在合成2-
氨基-2-去
氧-β-
D-半乳糖苷-(1→4)-2-
氨基-2-去
氧-β-
D-半乳糖苷
12、
16a和
17a的过程中,对最常见的糖基化方法的效率进行了系统研究。由于糖基受体轴向OH(4)基团的低反应性,也形成了具有α(1→4)键的二糖
16b和
17b。证实了在糖基化步骤中,乙基
硫基团从糖基受体
8的还原端出现意外的分子间迁移,到糖基供体
4的活化形式的还原端,形成乙基
硫基衍
生物3a。为了制备具有
半乳糖构型的糖基供体和糖基受体,采用了基于4-
O-甲磺基衍
生物与具有
葡萄糖构型的适当合成子的对映异构化的方法
2a和
2b。