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Abstract: siRNAs modified with morpholino nucleoside analogues were synthesized and their biological properties were examined in details. The gene silence abilities of modified siRNAs were correlated to the positions of the modifications, some of which appeared to be more potent than the native siRNA. The 3′-end modification improved the stability of siRNAs in serum significantly. Furthermore, the dose–response and time-course experiments demonstrated that the siRNAs with 3′-end modification have potent gene silence activity at lower concentration and prolonged action time. These favorable properties make the morpholino modified siRNA a potentially useful tool in therapeutic applications. [Copyright &y& Elsevier]

Abstract: Chimeric oligonucleotides with the novel morpholino modification and the phosphoramidate linkers have been synthesized and characterized. These oligonucleotides showed moderate thermal stability with complementary RNA and DNA, and enhanced resistance toward the nuclease (t 1/2 >10h). The phosphoramidate linker made the synthesis of such oligonucleotides applicable on a DNA synthesizer. Under the acidic condition (pH 3.0), the phosphoramidate linkers were readily cleaved, and such property might be useful for the DNA-sequence determination. [Copyright &y& Elsevier]