The synthesis and biochemical utility of modified oligonucleotides containing diphosphodiester internucleotide linkages. The synthesis of these compounds was carried out using diphosphitylating reagents. Oligonucleotides containing diphosphate diester bridges wherein said oligonucleotides are synthesized via a solid-phase synthesis strategy to form modified oligonucleotides. Diphosphitylating, triphosphitylating, tetraphosphitylating, β-triphosphitylating, bifunctional diphosphitylating, bifunctional triphosphitylating, and bifunctional tetraphosphitylating reagents wherein, the phosphorus atoms are linked together through oxygen, sulfur, amino, or methylene groups and/or are substituted with chlorine, diisopropylamine and cyanoethoxy groups.