STEREOSPECIFIC SYNTHESIS OF NUCLEOSIDE ANALOGS

羟胺衍生物的环化具有高立体选择性 从而得到几类生物学上有趣的分子， 氨基糖和核苷的类似物。 例如高 在羟胺环加成反应中观察到立体选择性 衍生物到无环的？，?-不饱和酯 加合物为 随后在温和条件下环化，得到单一异构体 的异恶唑烷-5-酮，其易于转化为乙酸保护的 异恶唑烷-5-醇。 这些中间体的偶联和 核苷碱基给？高顺式异恶唑烷基核苷 在非金属螯合物中很少观察到的选择性 2-脱氧呋喃糖基偶联反应的情况。 EI-MS、FAB-MS和精确 质量测量已被用于表征这些产品。

Hydroxylamine derivatives are cyclized with high stereoselectivity to give several classes of biologically interesting molecules such as the analogs of aminosugar and nucleoside. For example, high stereoselectivity was observed in the cycloaddition of hydroxylamine derivatives to acyclic ?, ?-unsaturated esters. The adducts were subsequently cyclized under mild conditions to afford a single isomer of isoxazolidin-5-ones which was easily converted to acetate-protected isoxazolidin-5-ols. The coupling of these intermediates and nucleoside bases gave ?-isoxazolidinyl nucleosides with high cis selectivity which has rarely been observed in the nonmetal-chelated cases of 2-deoxyfuranosyl coupling reactions. EI-MS, FAB-MS and exact mass measurements have been used to characterize these products.