Oligonucleotide synthesis by the use of a 2-(levulinyloxymethyl)-5-nitrobenzoyl group as the novel base-labile protecting Group for the 5′-hydroxyl groups of ribonucleoside and 2′-deoxyribonucleoside 3′-phosphoramidites

A novel 2-(levulinyloxymethyl)-5-nitrobenzoyl (LMNBz) protecting group for the 5′ position of nucleoside 3′-phosphoramidites was successfully applied to the solid-phase synthesis of both an oligodeoxyribonucleotide (TpTpT and TpTpTpT) and an octaribonucleotide in combination with a 2′-O-Thp protecting group (UpCpApGpUpUpGpG). The LMNBz group was simply unmasked due to its base-labile property by a two-step procedure, i.e., treatments with 0.5 M hydrazine hydrate in 1:4 acetic acid - pyridine, and then with 0.5 M imidazole in acetonitrile.