Luisier Samuel, Leumann Christian J
Department of Chemistry and Biochemistry, University of Bern, Switzerland.
Chembiochem. 2008 Sep 22;9(14):2244-53. doi: 10.1002/cbic.200800322.
The synthesis of two novel pyrimidine bicyclonucleosides (bc(ox)-nucleosides) has been accomplished. These bicyclonucleosides each carry a lipophilic benzyloxime substituent on the carbocyclic ring and show improved conformational similarity to 2'-deoxyribonucleosides as shown by their X-ray structures. The thymine-containing bc(ox)-nucleoside was converted into the corresponding phosphoramidite building block and incorporated into oligodeoxyribonucleotides by standard phosphoramidite chemistry. T(m) data with complementary RNA and DNA were measured and compared to corresponding cases of natural and unfunctionalized bc-DNA. It was found that single incorporations of bc(ox) residues destabilize duplexes by roughly 5 degrees C per modification. The destabilization was found to be due to the oxime substituent and not to the bicyclic scaffold itself. No significant alteration of the base-pairing selectivity as a function of the modification was observed. With RNA (but not with DNA) as a complement the relative thermal destabilization of bc(ox)-oligothymidylates was gradually reduced and converted into a stabilizing interaction with increasing numbers of consecutive modifications. While no cellular uptake of bc(ox)-oligonucleotides into HeLa cells occurred without transfecting agents, a significant increase in the transfection rate relative to unmodified DNA was observed in complexation with lipofectamine.
两种新型嘧啶双环核苷（bc(ox)-核苷）的合成已经完成。这些双环核苷在碳环上均带有亲脂性苄基肟取代基，并且如X射线结构所示，它们与2'-脱氧核糖核苷具有更高的构象相似性。含胸腺嘧啶的bc(ox)-核苷被转化为相应的亚磷酰胺砌块，并通过标准亚磷酰胺化学方法掺入到寡脱氧核糖核苷酸中。测量了与互补RNA和DNA的熔解温度（Tm）数据，并与天然和未功能化的bc-DNA的相应情况进行了比较。发现单次掺入bc(ox)残基会使双链体每修饰一处大约不稳定5℃。发现这种不稳定是由于肟取代基而非双环支架本身。未观察到碱基配对选择性随修饰而发生显著改变。以RNA（而非DNA）作为互补链时，随着连续修饰数量的增加，bc(ox)-寡胸苷酸的相对热稳定性逐渐降低并转变为稳定相互作用。在没有转染剂的情况下，bc(ox)-寡核苷酸不会被HeLa细胞摄取，但与脂质体转染试剂复合时，相对于未修饰的DNA，转染率显著提高。
