Per-O-acetylated N-acetylneuraminyl-α-(2→3)-galactopyranose was prepared in three steps in good overall yield from sialyl-α-(2→3′)-lactose by regioselective cleavage of the galactosyl-β-(1→4)-glucose linkage by acetolysis and then readily converted into the corresponding disaccharide 1-trichloroacetimidate or ethyl thioglycoside, valuable synthetic blocks for the preparation of complex sialylated oligosaccharides. The N-acetyl group in the disaccharide thioglycoside was replaced by an N-Boc one via intermediate formation of a mixed N-Ac-N-Boc imide followed by chemoselective de-N-acetylation with hydrazine hydrate in DMF. An example of application of the disaccharide thioglycoside for the preparation of a spacer-armed hexasaccharide SLex is described.
通过乙酰分解半
乳糖基-δ²-(1→4)-
葡萄糖连接,以半
乳糖基-δ²-(2→3′)-
乳糖为原料,分三步制备了过-O-乙酰化的 N-乙酰神经
氨酰-δ-(2→3)-
吡喃半
乳糖,总体收率良好,然后很容易转化为相应的 1-三
氯乙酰亚
氨酸二糖或乙基
硫代糖苷、这些都是制备复杂的苷元化
寡糖的重要合成砌块。
硫代糖苷二糖中的 N-乙酰基被 N-叔丁氧羰基取代,中间形成混合 N-Ac-N-Boc
亚胺,然后在
DMF 中用
水合
肼进行
化学选择性去 N-乙酰化。文中举例说明了
硫代糖苷二糖在制备间隔臂六糖 SLex 中的应用。