Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from d-xylose. The glycosyl donor 14 was synthesized from d-xylose, using cyclization of dimesylate 10 with sodium sulfide as a key step. Cyclization proceeded in pure SN2 reaction without going through SN1 reaction in the presence of an allylic functional group at low reaction temperature
                                    从d-
木糖开始,已经合成了新的
硫代异
嘧啶和被环外亚甲基取代的
嘌呤核苷。糖基供体14是由d-
木糖合成的,使用二
甲磺酸盐10与
硫化
钠的环化作为关键步骤。在烯丙基官能团的存在下,在低反应温度(0°C)下,在极性溶剂(
DMF)中,环化反应在纯S N 2反应中进行,而没有经过S N 1反应,得到化合物12为主要产物。在较高温度下,S Ñ 2'产物11几乎完全作为主要产物而获得。另一方面,糖基化在Mitsunobu条件下用14-
氯嘌呤14制得所需的S N 2产物26,而
钯催化的糖基化导致S N 2'产物34的唯一形成。