(7-Methoxy-2-oxo-2H-chromen-4-yl)-acetic acid-d 6 is the deuterium labeled MCA. MCA is a coumarin derivative. MCA quantitates platelet-activating factor by high-performance liquid chromatography with fluorescent detection. MCA can modify FRET peptide substrates for analyzing protease activities. (7-Methoxy-2-oxo-2H-chromen-4-yl)-acetic acid-d6 is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.