Synthesis of oligonucleotides with sequences identical with or analogous to the 3′ - end of I6S ribosomal RNA of escherichia coli: Preparation of A-C-C-U-C-C via the modified phosphotriester method

A combination of two different methods for the synthesis of oligoribo-nucleotides, i.e. the two-step phosphotriester method with 2-chlorophenyl phosphate as bifunctional phosphate source and the modified triester method with 2,2,2-trichloroethyl 2-chlorophenyl phosphorochloridate as monofunc-tional phosphate source, is applied for the synthesis of the fully-protected hexaribonucleotide A-C-C-U-C-C. The two-step method is used for the synthesis of the required dinucleoside monophosphates 9, 10 and 11 Application of the modified triester method for the coupling of the oligonucle-otide blocks results in the formation of the fully-protected hexamer 15. Furthermore, attention is paid to 2,4,6-triisopropylbenzsnesulphonyl 4-nitroimidazolide as a new condensing agent for the coupling of larger oligonucleotide blocks.