Based on the above and on the remarkable properties of the
2
′-O,
4
′-C-methylene bridged LNA monomers it was decided to synthesise oligonucleotides comprising one or more
2
′-O,′-C-methylene-&bgr;-D-xylofuranosyl nucleotide monomer(s) as the first stereoisomer of LNA modified oligonucleotides. Modelling clearly indicated the xylo-LNA monomers to be locked in an N-type furanose conformation. Whereas the parent
2
′-deoxy-&bgr;-D-xylofuranosyl nucleosides were shown to adopt mainly an N-type furanose conformation, the furanose ring of the
2
′-deoxy-&bgr;-D-xylofuranosyl monomers present in xylo-DNA were shown by conformational analysis and computer modelling to prefer an S-type conformation thereby minimising steric repulsion between the nucleobase and the
3
′-O-phopshate group (Seela, F.; Wömer, Rosemeyer, H.
Helv. Chem. Acta
1994, 77, 883
). As no report on the hybridisation properties and binding mode of xylo-configurated oligonucleotides in an RNA context was believed to exist, it was the aim to synthesise
2
′-O,
4
′-C-methylene-&bgr;-D-xylofuranosyl nucleotide monomer and to study the thermal stability of oligonucleotides comprising this monomer. The results showed that fully modified or almost fully modified Xylo-LNA is useful for high-affinity targeting of complementary nucleic acids. When taking into consideration the inverted stereochemistry at C-
3
′ this is a surprising fact. It is likely that Xylo-LNA monomers, in a sequence context of Xylo-DNA monomers, should have an affinity-increasing effect.
基于上述和2′-O,4′-C-亚
甲基桥联的LNA单体的显著特性,决定合成包含一个或多个2′-O,4′-C-亚
甲基-&bgr;-
D-木糖呋喃核苷单体的寡
核苷酸,作为LNA修饰寡
核苷酸的第一个立体异构体。建模清楚地表明,
木糖-LNA单体被锁定在N-型
呋喃糖环构象中。而父代2′-
脱氧-&bgr;-
D-木糖呋喃核苷被显示主要采用N-型
呋喃糖环构象,通过构象分析和计算建模显示,存在于
木糖-DNA中的2′-
脱氧-&bgr;-
D-木糖呋喃单体的
呋喃环更倾向于S-型构象,从而最小化核碱基和3′-O-
磷酸基团之间的立体排斥(Seela, F.; Wömer, Rosemeyer, H.Helv. Chem. Acta1994, 77, 883)。由于在RNA环境中对
木糖构型的寡
核苷酸的杂交性能和结合模式没有相关报告,因此旨在合成2′-O,4′-C-亚
甲基-&bgr;-
D-木糖呋喃核苷单体,并研究包含该单体的寡
核苷酸的热稳定性。结果表明,完全修饰或几乎完全修饰的
木糖-LNA对于高亲和力靶向互补
核酸是有用的。考虑到C-3′的反向立体
化学,这是一个令人惊讶的事实。很可能
木糖-LNA单体在
木糖-DNA单体序列环境中会具有增强亲和力的效果。