Active monomeric nucleotide intermediate in the oligonucleotide synthesis

The interaction of 3′ - O - acetylthymidine - 5′ - phosphate (pT-Ac) and p - nitrophenylphosphate (pPhNO₂) with triisopropylbenzenesulphonyl chloride (TPS) in pyridine was studied by the pulsed NMR spectroscopy on ³¹P nuclei. The esters investigated were shown to convert to the corresponding disubstituted pyrophosphates, trisubstituted tripolyphosphates and compounds showing a singlet displaced 5–8 ppm from the original ester. The latter are the main final products of the interaction of nucleotide and pPhNO₂ with TPS. The investigation of the chemical conversion of a pT-Ac derivative with a 5·1 ppm shift showed that this product is a powerful phosphorylating reagent. It was shown that this active derivative contains one P atom in accordance with the structure of monomeric metaphosphoric acid ester proposed by Todd for these compounds. The reaction of monomeric metaphosphate with 5′-O-tritylthymidine results information of a compound, containing stoichiometric amounts of pT-Ac and 5′ - O - tritylthymidilyl - (3′ → 5′) - 3′ - O - acetylthymidine residues. This compound was identified as a trisubstituted P¹ - 5′ - O - trityl - P¹ - P² -bis -(3′ - O - acetylthymidine) - pyrophosph