Synthesis and properties of morpholino chimeric oligonucleotides

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 (t1/2 > 10 h). 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.