An improved synthesis of the dinucleotides pdCpA and pdCpdA

An improved route was developed for the preparation of the dinucleotide hybrid 5'-O-phosphoryl-2'-deoxycytidylyl-(3'--> 5')adenosine (pdCpA) 7. This simple and concise synthesis involves the successive coupling of 2-cyanoethyl N, N, N', N'-tetra- isopropylphosphorodiamidite with 4-N-benzoyl-5'-O-(4, 4'-dimethoxytrityl)-2'-deoxy-cytidine 1 and 6-N,6-N,2'-O,3'-O-tetrabenzoyladenosine 2 as the key step. Some dinucleotide derivatives bearing different protecting groups were also synthesized and the selective deprotection conditions were studied in detail. The utility and efficiency of this approach has been further demonstrated by its application to the synthesis of total DNA dinucleotide pdCpdA 17 and total RNA dinucleotide 21.