Pyrazolopyrimidine nucleosides. Part VIII The synthesis of certain 4-substituted pyrazolo[3,4-d]pyrimidine nucleosides

1-(β-D-Ribofuranosyl)pyrazolo[3,4-b]pyrimidine-4-thione ( 6 ), obtained by a three-step synthesis from allopurinol riboside (3), was treated with certain alkyl and aryl halides to provide the corresponding 4-alkylthio derivatives. The nucleoside 4-methylthio-1-(β-D-ribofuranosyl)pyra-zolo[3,4-d]pyritnidine ( 7 ) has served as the precursor for the preparation of the 4-methylamino ( 11 ), 4-dimethylamino ( 12 ), 4-hydrazino ( 13 ), and the 4-hydroxylamino ( 14 ) analogs.