Phenyl 1-thio-β-D-galactopyranoside (1) was converted into two sulfoxide glycosyl donors: phenyl (2,3,4,6-tetra-O-benzyl)-1-thio-β-D-galactopyranoside S-oxide (3) and phenyl (2,3,4,6-tetra-O-pivaloyl)- 1-thio-β-D-galactopyranoside S-oxide (5). These glycosyl donors were then each reacted with Na- fluorenylmethoxycarbonyl-trans-4-hydroxy-L-proline allyl ester (7). The glycosylation reactions were conducted at -70°C with triflic anhydride as promotor, in the presence of 2,6-di-tert-butyl-4-methylpyridine. In the case of the perbenzylated sulfoxide donor (3), the major product was Na-fluorenylmethoxycarbonyl-trans-4-hydroxy- 4-O-[(2,3,4,6-tetra-O-benzyl)-a-D-galactopyranosyl]-L-proline allyl ester (8a). In dichloromethane, the a-to-β ratio was 3 : 1 and in toluene this improved to 5 : 1, with a combined yield of 41%. In the case of the perpivaloylated sulfoxide donor (5), Na-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-pivaloyl)-β-D- galactopyranosyl]-L-proline allyl ester (9) was obtained as the sole glycoside product in 46% yield.

中文翻译：

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亚砜糖基化法合成反式4-羟基-L-脯氨酸D-吡喃半乳糖苷

苯基 1-硫代-β-D-吡喃半乳糖苷 (1) 转化为两个亚砜糖基供体：苯基 (2,3,4,6-四-O-苄基)-1-硫代-β-D-吡喃半乳糖苷 S-氧化物(3) 和苯基 (2,3,4,6-四-O-新戊酰基)-1-硫代-β-D-吡喃半乳糖苷 S-氧化物 (5)。然后这些糖基供体各自与Na-芴基甲氧基羰基-反式-4-羟基-L-脯氨酸烯丙酯(7)反应。糖基化反应在 -70°C 下以三氟甲磺酸酐作为促进剂，在 2,6-二叔丁基-4-甲基吡啶存在下进行。在过苄基亚砜供体 (3) 的情况下，主要产物是 Na-芴基甲氧基羰基-反式-4-羟基-4-O-[(2,3,4,6-四-O-苄基)-αD-吡喃半乳糖基]-L-脯氨酸烯丙酯 (8a)。在二氯甲烷中，α 与 β 的比率为 3:1，在甲苯中这一比例提高到 5:1，总产率为 41%。