coupling of the corresponding D-glucopyranosyl donor 19 with 13 led to a much higher β/α ratio (2/1). By changing the conformation of the acceptor into the 1,6-anhydro-L-idopyranose acceptor 23, 90% of the desired β-coupled disaccharide was obtained in the glycosylation with galactopyranosyl donor 12. Finally it was found that the α/β ratio of the condensation with 25, promoted by an insoluble silver salt
为了合成Galß(1 4)IdoA二糖1,在不同条件下,用不同保护的D-
吡喃半
乳糖基供体进行
L-艾杜糖酸衍
生物5和13和L-
吡喃
葡萄糖衍
生物21的几个糖基化反应。已经发现,即使当供体在C-2处包含一个参与基团时,这些偶联反应也主要导致不希望的α-糖苷间键的形成。另一方面,相应的
D-吡喃葡萄糖基供体19与13的偶联导致更高的β/α比(2/1)。通过将受体的构型改变为1,6-脱
水-L-
吡喃
葡萄糖受体23,用半
乳糖吡喃糖基供体12进行糖基化反应后,可获得90%的所需β偶联二糖。最终发现,由不溶性
银盐促进的与25的缩合的α/β比以不寻常的方式受到半
乳糖基
溴化物上取代基的影响。