1-Cyclopropyl-7-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid-d4 is labelled 1-Cyclopropyl-7-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid (C989220) which can be used to prepare iminoquinolinecarboxamides. 1-Cyclopropyl-7-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid (C989220) can also be used as a reagent to prepare 1-alkyl-1,4-dihydro-4-imino-3-quinolinecarboxylic acid derivatives.