Figure 1.

Structures of BAAA-DA, BAAA, and BAA. BAAA-DA was synthesized by the bonding of the fluorescent compound BODIPY FL,SE to AAA-DA. BAAA-DA is converted to BAAA in the presence of acid with a t_1/2 of approximately 15 min under the conditions described in Materials and Methods. When cells are stained with BAAA, ALDH then converts BAAA into BAA, which is retained intracellularly because of its net negative charge. The structures of BAAA-DA and BAAA as well as the kinetics of conversion between these compounds were determined by ¹H-NMR spectroscopy.