Syntheses of Glycyrrhetic Acid .ALPHA.-Diglycosides and Enol .ALPHA.-Glycosides.
                                
                                    
                                        作者:Setsuo SAITO、Shigeya SUMITA、Yasuhiko KANDA、Yuka SASAKI                                    
                                    
                                        DOI:10.1248/cpb.42.1016
                                    
                                    
                                        日期:——
                                    
                                    Glycyrrhetinate α-monoglycoside derivatives 8, 10 and 12, all having a trichloroacetyl group at the C-2 position of the pyranose ring, were treated with NH3-saturated ether at 0°C to give the corresponding alcohols 13, 15 and 17, accompanied by 2'-chloroderivatives, 14, 16 and 18, respectively. Glycosylations of the alcohols 13, 15 and 17 with methyl 2, 3, 4-tri-O-acetyl-α-D-glucuronatopyranosyl bromide 19 in the presence of AgOTf in dry CH2Cl2 gave the corresponding α-diglycosides 20, 22 and 24 together with the enol α-glycosides 21, 23 and 25, respectively. Glycosylations of the diglycoside derivatives 20, 22 and 35 having no reactive OH group in the molecules with 19 for longer reaction times gave quantitatively the enol α-glycoside derivatives 21, 23 and 36, respectively. Glycosylation of the monoglycoside derivative 37, which has a poorly reactive OH group at the C-4 position on the pyranose ring, with 19 gave an enol α-glycoside 38. The mechanism of the formation of enol α-glycosides was investigated. Removal of the protecting groups of 20, 22 and 24 by successive treatment with 1.5N NaOMe in MeOH and 5% KOH in EtOH-H2O (1 : 1) gave the free α-diglycosides 26-28, and removal of those of 31, 21, 23, 25 and 36 by treatment with 5% KOH in EtOH-H2O (1 : 1) under reflux gave the free enol α-glycosides 41-45, respectively.
                                    甘草酸α-
单糖苷衍
生物 8、10 和 12 均在
吡喃糖环的 C-2 位上具有三
氯乙酰基,在 0°C 下用 NH3 饱和醚处理后,可分别得到相应的醇 13、15 和 17 以及 2'-
氯二衍
生物 14、16 和 18。在 AgOTf 存在下,醇 13、15 和 17 与 2,3,4-三-O-乙酰基-α-D-
葡糖酸吡喃糖基
溴化物 19 在干燥的 
CH2Cl2 中发生糖基化反应,分别得到相应的 α-二糖苷 20、22 和 24 以及烯醇 α-糖苷 21、23 和 25。将分子中没有反应性 OH 基团的二糖苷衍
生物 20、22 和 35 与反应时间较长的 19 进行糖基化,可分别定量得到烯醇 α-糖苷衍
生物 21、23 和 36。
单糖苷衍
生物 37 在
吡喃糖环的 C-4 位上有一个反应性很差的 OH 基团,用 19 进行糖基化反应可得到烯醇 α-糖苷 38。研究了形成烯醇 α-糖苷的机理。用 1.5N NaOMe in MeOH 和 5% KOH in EtOH-
H2O (1 : 1) 相继处理 20、22 和 24,去除其保护基团,得到游离的 α-二糖苷 26-28;用 5% KOH in EtOH-    (1 : 1) 在回流下处理 31、21、23、25 和 36,去除其保护基团,分别得到游离的烯醇 α-糖苷 41-45。