Abstract The synthesis of oligonucleotides containing 2′-deoxy-5-methylisocytidine and 2′-deoxyisoguanosine using phosphoramidite chemistry in solid-phase oligonucleotide synthesis is described. Supporting previous observations, the N, N-diisobutylformamidine moiety was found to be a far superior protecting group than N-benzoyl for 2′-deoxy-5- methylisocytidine. 2′-Deoxy-N 2-[(diisobutylamino) methylidene]-5′-(4, 4′- ...