Synthesis of some modified 2′‐5′‐linked oligoriboadenylates of 2‐5A core

The synthesis of three analogues of 2′‐5′‐linked oligoriboadenylates is reported. Two trimers, having at the 2′‐end a 3′‐amino‐ (or 3′‐tetradecanamido)‐3′‐deoxy‐riboadenosine, were assembled via a phosphotriester approach. In the same way, we also prepared a tetramer carrying at the 2′‐end β‐L‐riboadenosine instead of β‐D‐riboadenosine. The non‐terminal building unit 3′,5′‐ O ‐(tetraisopropyldisiloxane‐1,3‐diyl)‐ N 6 ‐benzoyladenosine and the appropriately protected modified riboadenosines were coupled using the phosphorylating agent 2‐chlorophenyl‐ O,O‐bis (1‐benzotriazolyl) phosphate. The removal of all protecting groups from the intermediate trimers and tetramer was effected by ammonolysis, followed by treatment with fluoride ions.