中文摘要：

为了系统研究异核苷嵌杂寡聚核苷酸的生物学效应，对L-胞嘧啶异核苷的全合成工艺进行了详细研究.以L-核糖为起始原料，以尿嘧啶碱基对5-O-三苯基甲基-2，3-O-环硫酸酯-1-脱氧-L-核糖3位的区域选择性亲核取代反应为关键步骤，经过9步反应，以28.5%的总收率合成得到了L-胞嘧啶异核苷.条件优化表明，以碳酸铯为碱可以显著提高N-1核苷键生成的产率和减少副反应的发生，同时分离得到了副产物N-1，N-3双核糖尿嘧啶异核苷.该工艺路线反应条件温和，反应中间体容易纯化，总产率高，可以作为结构类似异核苷的通用合成路线.

英文摘要：

In order to systematic study the biological effects of isonucleoside incorporated oligonucleotides, an efficient synthetic process for iso-L-cystidine was investigated in present paper. Using L-ribose as starting material, iso-L-cystidine was obtained in 9 steps and 28.5% overall yield. The key step was the regioselective nucleophilic substitution of 5-O-triphenylmethane-2,3-O-cyclic sulfate with uracil. After extensive optimization, it was found that using cesium carbonate as base can improve significantly the N-1 glycosidic bond formation and reduce the side reactions. At the same time, a N-1,N-3 doublic 1-deoxyribose substituted iso-L-uridine was identified for the first time. The present reported synthetic process has the merits of mild reaction conditions, easy purified intermediates and high overall yield, which could be used as a general synthetic approach for the preparation other related isonucleoside.