Synthesis of deuterium-labeled 2-quinoxalinecarboxylic acid and 3-methylquinoxaline-2-carboxylic acid from deuterium aniline

An efficient and simple synthetic route of deuterium-labeled 2-quinoxalinecarboxylic acid- d 4 (QCA- d 4 ) and 3-methylquinoxaline-2-carboxylic acid- d 4 (MQCA- d 4 ) is presented with 99.9% and 99.6% isotopic enrichment using aniline- d 5 as labeled starting material. Their chemical structures were confirmed by 1 H NMR, and their isotopic abundance was determined by mass spectrometry analysis.