Reaction between 1-arenesulphonyl-3-nitro-1,2,4-triazoles and nucleoside base residues. Elucidation of the nature of side-reactions during oligonucleotide synthesis.

The protected guanosine and uridine derivatives (3a, 3b and 4) react with 1-(mesitylene-2-sulphonyl)-3-nitro-1,2,4-triazole (MSNT, 2a) to give 5a, 5b and 7, respectively: 9 is converted into 10 in the same way. The reactions proceed more rapidly in the presence of diphenyl phosphate.