2-amino-4-oxo-1,7-dihydropyrrolo[4,5-e]pyrimidine-5-carbonitrile 2-amino-4-keto-1,7-dihydropyrrolo[4,5-e]pyrimidine-5-carbonitrile 7-Cyano-7-carbaguanine 7-Cyano-7-deazaguanine C15996 PQ0