Syntheses of 8-aminoimidazo[4′,5′:5,6]pyrido[2,3-d]pyrimiciines: Linear tricyclic analogs of adenine

The syntheses of 8-aminoimidazo4′,5′:5,6]pyrido2,3-d]pyrimidines (7), stretched-out versions of the naturally occuring nucleoside base adenine, are reported. Their preparation involves conversion of purine into 5-arninoimidazo4,5-b]pyrimidine-6-carbonitrile ( 1 ) by reaction with malononitrile, followed by construction of the pyrimidine ring in two steps via the ethoxymethylene derivative 3 . 8-Azapurine can be converted to 8-amino-1,2,3-triazolo4′,5′:5,6]pyrido2,3-d]pyrimidines 8 in a similar fashion.