Kovác P
Carbohydr Res. 1986 Oct 1;153(2):237-51. doi: 10.1016/s0008-6215(00)90266-0.
Bromoacetylation of methyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (1) followed by cleavage of the methoxyl group from the resulting 6-O-bromoacetyl derivative 2 with 1,1-dichloromethyl methyl ether gave 2,3,4-tri-O-benzoyl-6-O-bromoacetyl-alpha-D-galactopyranosyl chloride (3). Reaction of 3 with 1, promoted by silver trifluoromethanesulfonate, afforded methyl O-(2,3,4-tri-O-benzoyl-6-O-bromoacetyl-beta-D-galactopyranosyl)-(1----6) -2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (12), bearing at O-6 of its non-reducing end-group the selectively removable bromoacetyl group. This was O-debromoacetylated and the disaccharide nucleophile 15 formed was again treated with 3, to give the analogous trisaccharide 18. This sequence of reactions was repeated to afford the analogous tetrasaccharide 20, showing the feasibility of stepwise construction of the title oligosaccharides. Similar reactions of 3 with 1,2,3,4-tetra-O-benzoyl-alpha- (7) and beta-D-galactopyranose (5) gave, respectively, O-(2,3,4-tri-O-benzoyl-6-O-bromoacetyl-beta-D-galactopyranosyl)-(1----6) -1,2,3,4-tetra-O-benzoyl-alpha- (14) and beta-D-galactopyranose (13). These could be separately converted into the same glycosyl halide, namely, alpha-(2,3,4-tri-O-benzoyl-6-O-bromoacetyl-beta-D-galactopyranosyl)-(1-- --6)-2,3,4-tri-O-benzoyl-alpha-D-galactopyranosyl chloride (16), by cleavage with 1,1-dichloromethyl methyl ether. The chloride 16 was treated with tri- and tetra-saccharide nucleophiles analogous to 15 to give, respectively, the corresponding pentasaccharide 23 and the hexasaccharide 25, demonstrating the possibility of the blockwise construction of higher beta-(1----6)-linked D-galacto-oligosaccharides. The disaccharide 12 was also obtained by the reaction of 1,2,3,4-tetra-O-benzoyl-6-O-bromoacetyl-beta-D-galactopryanose (6) with 1 in the presence of trimethylsilyl trifluoromethane-sulfonate. Similarly, the trisaccharide 18 and the tetrasaccharide 20 were obtained by the treatment of 13, respectively, with 1 and 15, showing that, as with their 1-O-acetyl counterparts, beta-1-benzoates of saccharides bearing at O-2 a group capable of neighboring-group participation can act under these conditions as glycosyl donors. Crystalline methyl beta-glycosides of (1----6)-beta-D-galacto-tetraose (22), -pentaose (24) and -hexaose (27) have been obtained for the first time, by deacylation (Zemplén) of their fully protected precursors.
2,3,4-三-O-苯甲酰基-β-D-吡喃半乳糖苷甲酯（1）进行溴乙酰化反应，随后用1,1-二氯甲基甲醚从所得的6-O-溴乙酰基衍生物2上裂解掉甲氧基，得到2,3,4-三-O-苯甲酰基-6-O-溴乙酰基-α-D-吡喃半乳糖基氯（3）。在三氟甲磺酸银的促进下，3与1反应，得到甲基O-(2,3,4-三-O-苯甲酰基-6-O-溴乙酰基-β-D-吡喃半乳糖基)-(1→6)-2,3,4-三-O-苯甲酰基-β-D-吡喃半乳糖苷（12），其非还原端基的O-6位带有可选择性去除的溴乙酰基。对其进行O-脱溴乙酰化反应，形成的二糖亲核试剂15再次用3处理，得到类似的三糖18。重复这一反应序列得到类似的四糖20，表明逐步构建标题寡糖的可行性。3与1,2,3,4-四-O-苯甲酰基-α-D-吡喃半乳糖（7）和β-D-吡喃半乳糖（5）的类似反应，分别得到O-(2,3,4-三-O-苯甲酰基-6-O-溴乙酰基-β-D-吡喃半乳糖基)-(1→6)-1,2,3,4-四-O-苯甲酰基-α-D-吡喃半乳糖（14）和β-D-吡喃半乳糖（13）。通过用1,1-二氯甲基甲醚裂解，它们可分别转化为相同的糖基卤化物，即α-(2,3,4-三-O-苯甲酰基-6-O-溴乙酰基-β-D-吡喃半乳糖基)-(1→6)-2,3,4-三-O-苯甲酰基-α-D-吡喃半乳糖基氯（16）。用类似于15的三糖和四糖亲核试剂处理氯化物16，分别得到相应的五糖23和六糖25，证明了逐步构建更高的β-(1→6)-连接的D-半乳糖寡糖的可能性。二糖12也可通过在三甲基甲硅烷基三氟甲磺酸盐存在下，1,2,3,4-四-O-苯甲酰基-6-O-溴乙酰基-β-D-吡喃半乳糖（6）与1反应得到。类似地，通过分别用1和15处理13，得到三糖18和四糖20，表明与它们的1-O-乙酰基类似物一样，在O-2位带有能够参与邻基参与的基团的糖类的β-1-苯甲酸酯在这些条件下可作为糖基供体。通过对其完全保护的前体进行脱酰基反应（泽普林反应），首次获得了(1→6)-β-D-半乳糖四糖（22）、-五糖（24）和-六糖（27）的结晶甲基β-糖苷。
