Nucleosides part LXIV - Base-labile protecting groups for the oligoribonucleotide synthesis

New labile protecting groups for the anticipated synthesis of oligoribonucl eotides were developed and introduced via their carbonochloridates 8-11 at the 5 ' -O position of thymidine (15) to form 16, 18, 21, and 24 in good yi elds (Schemes 2 and 3). Similarly, the 5 ' -O-diphenylphosphinoyl(dpp)-prot ected thymidine derivative 27 was synthesized with diphenylphosphinoyl chlo ride 14 as the reactive reagent. With the help of the model compounds 16,18 , 21, 24, and 27, the deprotection rates of these functions towards base tr eatment were recorded to evaluate their usefulness as temporary protecting groups in RNA assembly (Table). Finally, the relative stability of the 2-(4 -nitrophenyl)ethoxycarbonyl (npeoc) protecting group towards bases confirme d its use as a permanent blocking group in our npe/npeoc strategy.