6-Amino-4-pyridazinecarboxylic Acid, can be used in the preparation of the Pyridazino[4,5-b]indole scaffold, which is a the core of wide variety of bio-active compounds.
Norbert, H., et al.: Concise syntheses of 5-substituted pyridazino[4,5-b]indolones and -diones, (VII), 16 (2008);