By the reaction of 7-deaza-2'-deoxyguanosine with a phosphorylation agent, for example phosphorus oxychloride, in a trialkyl phosphate, preferably trimethyl phosphate, as solvent and subsequent working up, there can be obtained the 5'-monophosphates of the general formula: ##STR3## wherein X is a hydrogen atom or an alkali metal, alkaline earth metal or ammonium ion.