'Ethylene-Bis[phosphonate] nucleic acids':: Novel monomeric synthons for the solid-phase synthesis of (P-CH2-CH2-P)-bridged oligonucleotides

An efficient synthesis of modified deoxyribonucleosidic building units, containing the 'ethylene-bisphosphonate nucleic acids'(EBPNAs) 1 or 2, has been developed. By means of solution-phase incorporation of 11, the oxidized form of 2, dinucleotide analogs of type 13 were prepared. The same strategy was used to incorporate 2 into the 5'-terminal position of the 12-mer homopolynucleotide methylphosphonate 14. A preliminary approach for solid-phase incorporation of the nucleosidic building block 1 into a preselected position of an oligonucleotide sequence to give 19 is presented, a reaction performed by means of a coupling strategy involving catalytic oxazaphospholidine-ring cleavage.