4-(2-Aminoethylamino)-7 H -benz[ de ]benzimidazo[2,1- a ]isoquinoline-7-one as a Highly Sensitive Fluorescent Labeling Reagent for Carnitine

4-(2-Aminoethylamino)-7H-benz[de]benzimidazo[2,1-a]isoquinoline-7-one, synthesized and identified by a HMBC study, can be used as a fluorescent labeling reagent for carnitine. The excitation and emission maxima in acetonitrile were observed at λ 454 and 508 nm, respectively. This reagent smoothly reacted with carnitine in the presence of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride to afford the corresponding amide under mild conditions. The detection limit (S/N > 3) of carnitine was ca. 12 fmol.