Derivatives of 5‐Oxy‐pyrido[2,3‐ b ]quinoxaline‐9‐carboxylic acid: A tricyclic system useful for the synthesis of potential intercalators

The synthesis of a new series of 5‐oxy‐pyrido[2,3‐ b ]quinoxaline‐9‐carboxamides 4a‐i and N 1 , N 2 ‐Bis(5‐oxy‐pyrido[2,3‐ b ]quinoxaline‐9‐benzoyl)ethylenediamine ( 5 ) is reported starting from 2‐chloro‐3‐nitropyri‐dine. Fundamental steps of the synthetic pathway are i) preparation of 2‐(3‐nitro‐pyridin‐2‐ylamino)benzoic acid ( 1 ) via copper‐catalyzed condensation of 2‐chloro‐3‐nitropyridine with o ‐anthranilic acid, ii) intramolecular cyclization of the acid 1 to 5‐oxy‐pyrido[2,3‐ b ]quinoxaline‐9‐carboxylic acid ( 2b ) upon treatment with concentrated sulfuric acid and oleum and iii) conversion of the acid 2 to the desired amides 4a‐i and 5 . Compounds 4a‐i and 5 are oxygenated azaanalogs of phenazines, a wellknown series of intercalators with cytotoxic activity.