Besides partial methylation of the phosphate group, especially above pH6, adenosine 5′-phosphate is methylted on N-i by dimethyl sulphate to yield N1-methyl-adenosine 5′-phosphate (II; R = H). The latter is quantitatively rearranged, by mild treatment with base, to 6-methylaminopurinerboside 5′-phosphate (I; R = H, R′ = Me). This is further converted to the corresponding pyrophosphate (I; R = PO(OH)2, R′ = Me) by reaction with benzyl N-cyclohexylphosphoramidate (III; R = cyclohexyl), followed by catalytic hydrogenolysis. P1-adenosine5′-P2-benzyl pyrophosphate (I; R = PO(OH)((OCH2Ph), R′ = H), obtained from adenosine 5′-phosphate and benzyl phosphoramidate (III; R = H), is methylated exclusively on N-i by dimethyl sulphate. Catalytic hydrogenolysis of the product yields N1-methyladenosine 5′-pyrophosphate (II; R = PO(OH)2). The latter is rearranged, by mild treatment with base, to the above-mentioned 6-methylamino-purineriboside 5′-pyrophosphate (I; R = PO(OH)2, R′ = Me).