Phosphorylation of Nucleosides with Phosphorus Oxychloride in Trialkyl Phosphate

Abstract

The reaction of guanosine and triethyl phosphate at 50°C for 15 min produced the guanosine-triethyl phosphate complex in which triethyl phosphate is coordinated to guanosine of high-anti form in a 1 : 1 molar ratio. During the conversion of guanosine to guanosine 5'-monophosphate with phosphorus oxychloride, the guanosine-triethyl phosphate complex showed excellent selectivity and high reactivity toward phosphorus oxychloride compared with those of guanosine. The rate of selective phosphorylation of guanosine into guanosine 5'-monophosphate was markedly improved by preheating the mixture of guanosine and triethyl phosphate at 50°C, followed by adding phosphorus oxychloride to the mixture at 0°C. Thus, the 5'-phosphorylation of guanosine with phosphorus oxychloride in triethyl phosphate is considered to progress via the guanosine-triethyl phosphate complex as the reaction intermediate.