mannose, the high α selectivity observed with C-mannosylation was reversed to high β selectivity if the C-5 alkoxyalkyl group were removed. An analysis of the conformational preferences of the intermediate oxocarbenium ions, including the mannosyl cation, as well as consideration of steric effects that develop in the transition states for nucleophilic attack provide explanations for these phenomena.
进行了与
甘露糖和其他
吡喃糖酶有关的
缩醛的C-糖基化的系统研究。C-5烷氧基烷基仅对立体选择性提供适度的影响。另一方面,对在C-2,C-3和C-4处带有烷氧基的戊基
吡喃糖的研究表明,烷氧基对选择性有重要影响。
甘露糖的情况下,与观察到的高选择性α Ç -mannosylation反向以高选择性β如果C-5的烷氧基烷基中除去。对中间氧碳鎓离子(包括
甘露糖基阳离子)的构象偏爱的分析,以及对亲核进攻过渡态中产生的空间效应的考虑,为这些现象提供了解释。