Nature of side-reactions in oligonucleotide synthesis involving arenesulphonyl derivatives of 3-nitro-1,2,4-triazole and related condensing agents.

The protected guanosine and uridine derivatives (10a, 10b and 11) react with MSNT (2a) to give the nitrotriazole derivatives (12a, 12b and 14, respectively); the 2'-deoxyguanosine derivative (16) is converted into 17 in the same way. All of these reactions proceed more rapidly in the presence of diphenyl phosphate (8). The starting materials (10b and 11, respectively) may easily be regenerated from 12b and 14 by treatment with N1,N1,N3,N3-tetramethylguanidinium syn-4-nitrobenzaldoximate in dioxan solution, when 14 is treated with ammonia in aqueous dioxan, cytidine is obtained. N-Acyl-2',3',5'-tri-O-acyl derivatives of adenosine and cytidine and 3',5'-di-O-acetylthymidine are unaffected by MSNT (2a) even in the presence of diphenyl phosphate (8). TPSNT (2b) reacts with 2-N-benzoylguanine and uracil residues in the same way as does MSNT (2a), but somewhat more slowly. MSTe (1; R = Me) reacts with 11 to give 19; however, its reaction with 10b is complete.