Department of Chemistry, Faculty of Science, York University, Toronto, ON M3J 1P3, Canada.
Chemistry Department, Faculty of Science, Arish University, Arish, Egypt.
Molecules. 2019 Sep 5;24(18):3235. doi: 10.3390/molecules24183235.
The coupling of 2-bromo-3-benzoyloxycyclobutanone with purine under basic conditions produces two regioisomers consisting of the and alkylated products in equal amounts in their racemic forms. The distribution of the isomers is consistent with the charge delocalization between the and positions of the purinyl anion. The structural assignments and relative stereochemistry of each regioisomer were based on 1 and 2D NMR techniques. The relative stereochemistry of the and substituents in each regioisomer was the orientation consistent with steric factors in the coupling step. The regioisomer was reduced with sodium borohydride to give the all cyclobutanol as the major product in a stereoselective manner. The alcohol was debenzoylated with sodium methoxide in a transesterification step to give the nucleoside analogue. The regioisomeric pyrimidine nucleosides were prepared by Vorbrüggen coupling of the 3-hydroxymethylcyclobutanone triflate with either thymine or uracil followed by stereoselective hydride addition. Regiospecificity of the coupling at the N-1 position was observed and stereoselective reduction to the trans-disubstituted cyclobutanol structure assignments was based on NMR data.
在碱性条件下，2-溴-3-苯甲酰基环丁酮与嘌呤偶联，生成两种比例相等的非对映异构体，即和烷基化产物。异构体的分布与嘌呤阴离子的和位置之间的电荷离域一致。每个区域异构体的结构分配和相对立体化学都是基于 1 和 2D NMR 技术。每个区域异构体中和取代基的相对立体化学是与偶联步骤中的空间因素一致的 取向。用硼氢化钠还原 区域异构体，以立体选择性方式得到主要产物全 环丁醇。在转酯化步骤中，用甲醇钠脱去 区域异构体的苯甲酰基，得到核苷类似物。通过 3-羟甲基环丁酮三氟甲磺酸酯与胸腺嘧啶或尿嘧啶的 Vorbrüggen 偶联，制备了区域异构体嘧啶核苷，然后进行立体选择性氢化加成。在 N-1 位置观察到偶联的区域特异性，并基于 NMR 数据对立体选择性还原到反式二取代环丁醇结构分配进行了评估。
