Investigation of the mechanism of the synthesis of oligonucleotides. IX. 31P NMR spectra of the active dinucleotide derivatives and their analogs.

The interaction of 3'-O-acetyldithymidilate (pdTpdT(Ac)), thymidine-3',5'-diphosphate (pdTp) and thymidine-3'-phenyl-phosphate-5'-phosphate (pdTpPh) with 2,4,6-triisopropylbenzene sulphonyl chloride (TPS) and N,N'-dicyclohexylcarbodiimide (DCC) in pyridine and dimethylformamide (DMF) was studied by pulsed NMR spectroscopy on phosphorus nuclei. Thymidine cyclic 3',5'-pyrophosphate and dimeric pyrophosphate derivatives were shown to be the main products of the reaction of pdTp with TPS and DCC. The former shows spin AB-system with the unusually large spin-spin coupling constant about 28Hz upfield to the signals of the dimeric pyrophosphates in NMR spectrum. Analogous spin AB-systems with large spin-spin coupling constants (up to 32 Hz) were observed in the spectra of the reaction mixtures of pdTpdT(Ac) with TPS or DCC and of pdTpPh with TPS. These spin AB-systems were ascribed to 3',5'-cyclic pyrophosphate derivatives of pdTpdT(Ac) and pdTpPh.