An Efficient Route to β-<scp>d</scp>-Isoxazolidinyl Nucleosides via Diastereoselective Michael Addition of Hydroxylamine to Unsaturated Esters
作者:Yuejun Xiang、Hung-Jang Gi、Deqiang Niu、Raymond F. Schinazi、Kang Zhao
DOI:10.1021/jo9710588
日期:1997.10.1
beta-D-isoxazolidinyl pyrimidine and purine nucleosides are described. Michael addition of N-methylhydroxylamine to alpha,beta-unsaturated esters was investigated. Both E- and Z-esters 10E and 10Z produced the same intermediates which were cyclized to isoxazolidin-5-ones 8 with high diastereoselectivity. The major isoxazolidin-5-one 8a was reduced and acetylated to acetate 11 for the preparation of nucleosides
描述了β-D-异恶唑啉基嘧啶和嘌呤核苷的对映选择性合成。研究了N-甲基羟胺向α,β-不饱和酯的迈克尔加成。E酯和Z酯10E和10Z均产生相同的中间体,它们以高非对映选择性环化成异恶唑烷-5-酮8。还原主要的异恶唑烷丁-5-酮8a并乙酰化成乙酸酯11以制备核苷。使用TMSOTf作为路易斯酸,使乙酸盐11与甲硅烷基化的胸腺嘧啶,尿嘧啶和N(4)-苯甲酰胞嘧啶偶联,得到相应的核苷衍生物。相关的嘌呤类似物是由BF(3).Et(2)O催化的乙酸酯11与甲硅烷基化的6-氯嘌呤缩合生成的。嘧啶和嘌呤类似物的顺式异构体主要形成是意外的,并研究了反应机理。将核苷中间体转化为相应的1,2-二醇,然后将其氧化并还原为所需的一元醇产物,例如14、16、19和24。