Nucleotides. Part LXXIII: Oligoribonucleotide Synthesis with the (2‐Cyano‐1‐phenylethoxy)carbonyl (2c1peoc) Group for the 5′‐Hydroxy Protection

The (2‐cyano‐1‐phenylethoxy)carbonyl (2c1peoc) group was developed as a new base‐labile protecting group for the 5′‐OH function in solid‐phase synthesis of oligoribonucleotides via the phosphoramidite approach. The half‐lives of its β ‐elimination process by 0.1 M DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene) were determined to be 7–14 s by HPLC investigations. The 2′‐OH function was protected with the acid‐labile tetrahydro‐4‐methoxy‐2 H ‐pyran‐4‐yl (thmp) group, while the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) groups were used for the protection of the base and phosphate moieties. The syntheses of the monomeric building blocks, both phosphoramidites and nucleoside‐functionalized supports, as well as the build‐up of oligoribonucleotides by means of this approach are described.