Substituted 7-aminopyrazolo pyrimidines

Aminopyrazolo[3,4-d]pyrimidines 257 were converted into the corresponding 4-aryl substituted derivatives 259 via treatment with alkyl nitrites and boiling in aromatic solvent. The isomer distribution of 259 prepared by these route was that predicted for a radical intermediate (ortho, meta, and para). The structure of isomers was established by H-NMR. Unusual fragmentation products were isolated these probably result from collapse of the radical intermediate 258 (83JOC4605). Methylation of 257 takes place at either N-1 or N-2. Further methylation affords methylamino derivatives structures of the products were established by C-NMR as well as by chemical methods (75JOC1822). 

Table I. Biological Activity of Substituted 7-Aminopyrazolo[4,3-d]pyrimidines (79)...

Several papers have appeared on tautomerism in pyrimidines, including the parent molecule, pyrimidyl-2- and -4-cyanoacetic esters, and AT-substituted 4-aminopyrazolo[3,4-< ]pyrimidines. The last-mentioned system (5) is in equilibrium with (6) in aqueous solution. Interconversion is catalysed by acid and base, and proceeds via either an intermediate cation that is common to both neutral tautomers or through the anion. Other studies of condensed systems include... 

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