Based on a pre-activation protocol, the stereoselectivity of oxazolidinone-protected amino sugar thioglycoside donors towards glycosylations can be controlled by additives. Either α- or β-selectivity could be obtained by changing additives. 2,4,6-Tri-tert-butylpyrimidine (TTBP) was the best β-directing additive, while thiophene worked as the best α-directing additive. The bifunctional additives such as tetrabutyl ammonium iodide (TBAI) afforded either α- or β-selectivity depending on the amount added. Poor α-selectivity of some glycosylations without any additives was greatly improved by adding TBAI or thiophene.
根据预激活方案,可通过添加剂控制
噁唑烷酮保护的
氨基糖
硫代糖苷给体对糖基化的立体选择性。通过改变添加剂可获得δ-或δ-选择性。2,4,6-三叔丁基
嘧啶(
TTBP)是最好的δ-定向添加剂,而
噻吩则是最好的δ-定向添加剂。双功能添加剂,如
四丁基碘化铵(TBAI),根据添加量的不同,可提供δ-或δ-选择性。添加 TBAI 或
噻吩后,一些未添加任何添加剂的糖基化反应的δ-选择性大大提高。