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A regioselective synthetic route to 2,8-disubstituted pyrido[3,4-b]pyrazines, by initial condensation reaction between suitable diaminopyridines and α-keto aldehydes equivalents, has been developed. Focusing on the functionalization on C-8, 2-aryl-8-bromo- and 8-amino-2-arylpyrido[3,4-b]pyrazines have been synthesized. Anilines, amides, and ureas have been introduced at the 8-position from key intermediates. 2,8-Disubstituted pyrido[3,4- b]pyrazines thus prepared were found to be of biological interest. [ABSTRACT FROM AUTHOR]

A four-step synthesis of 8-bromo-2,3-disubstituted pyrido[ 3,4-b]pyrazines and a six-step synthesis of 8-amino-2,3-disubstituted pyrido[3,4-b]pyrazines have been developed. A particularly valuable feature of this synthetic route is the possibility to build 2,3- disubstituted pyrido[3,4-b]pyrazines with a large variety of substituents in position 8 (aniline, amide, urea, thiourea). Our protocol was extended to the synthesis of 2,3,8-trisubstituted pyrido[2,3-b]pyrazines. [ABSTRACT FROM AUTHOR]