Saito S, Sumita S, Kanda Y, Sasaki Y
Faculty of Pharmaceutical Sciences, Josai University, Saitama, Japan.
Chem Pharm Bull (Tokyo). 1994 May;42(5):1016-27. doi: 10.1248/cpb.42.1016.
Glycyrrhetinate alpha-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 degrees 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-alpha-D-glucuronatopyranosyl bromide 19 in the presence of AgOTf in dry CH2Cl2 gave the corresponding alpha-diglycosides 20, 22 and 24 together with the enol alpha-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 alpha-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 alpha-glycoside 38. The mechanism of the formation of enol alpha-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 alpha-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 alpha-glycosides 41-45, respectively.
在吡喃糖环的C-2位均带有三氯乙酰基的甘草次酸α-单糖苷衍生物8、10和12，于0℃下用氨气饱和的乙醚处理，得到相应的醇13、15和17，同时分别伴有2'-氯衍生物14、16和18。在干燥的二氯甲烷中，醇13、15和17与2,3,4-三-O-乙酰基-α-D-葡糖醛酸吡喃糖基溴19在三氟甲磺酸银存在下进行糖基化反应，分别得到相应的α-二糖苷20、22和24以及烯醇式α-糖苷21、23和25。分子中无活性OH基团的二糖苷衍生物20、22和35与19进行较长时间的糖基化反应，分别定量得到烯醇式α-糖苷衍生物21、23和36。吡喃糖环C-4位带有活性较差的OH基团的单糖苷衍生物37与19进行糖基化反应，得到烯醇式α-糖苷38。对烯醇式α-糖苷的形成机制进行了研究。依次用甲醇中的1.5N甲醇钠和乙醇-水（1:1）中的5%氢氧化钾处理20、22和24，脱去保护基，得到游离的α-二糖苷26 - 28；在回流条件下，用乙醇-水（1:1）中的5%氢氧化钾处理31、21、23、25和36，脱去保护基，分别得到游离的烯醇式α-糖苷41 - 45。
