An improved phosphoramidite method is described to prepare oligonucleotides modified with the acyclic, achiral monomers 1. Examination of dimers, prepared on solid support or in solution, showed that phosphortriester dimers containing the allylic unit 1 were unstable towards bases, whereas phosphordiester dimers were stable. Phosphordiester dimers were obtained by replacing cyanoethyl phosphoramidites 2 with phosphoramidites 3, which gave phosphordiesters directly upon oxidation. The phosphordiester dimers were found to be stable towards capping and oxidation, but were somewhat labile towards acids. By reducing the contact time to acids during detritylation it was possible to prepare oligonucleotides containing 4 or 8 modified A, G or T units. The modified oligonucleotides hybridized to complementary DNA and RNA, although with reduced affinity (ΔTm per modification −1 to −5 °C).
描述了一种改进的
磷酰胺法,用于制备用非环状、无手性的单体1修饰的寡核苷酸。对在固相或溶液中制备的二聚体的研究表明,含有烯丙基单元1的
磷三酯二聚体对碱不稳定,而
磷二酯二聚体则稳定。通过用
磷酰胺基团3替换
氰乙基
磷酰胺基团2,可以获得
磷二酯二聚体,后者在氧化后可直接生成。发现
磷二酯二聚体对封闭和氧化稳定,但对酸有一定的敏感性。通过减少去三苷化过程中与酸的接触时间,可以制备含有4或8个修饰的A、G或T单位的寡核苷酸。这些修饰过的寡核苷酸能够与互补的DNA和RNA结合,但亲和力有所降低(每次修饰导致的ΔTm为−1到−5 °C)。