Since many years, we have been searching for "leads on new drugs" in tropical medicinal plants. In this study, we report a recent finding from Quassia amara, a tropical forest shrub of the Simaroubaceae family, distributed in South America. Q. amara contains alkaloids with canthin- and carboline-type compounds and quassinoids. This shrub is used as a folk medicine in Brazil and a bitter stomachic and antitumor agent. It is also known for its antimalarial and antivirus effects and efficacy in producing saliva and stimulating digestion. In the course of our research on finding active compounds of this plant, we discovered a new yellowish compound 1 that has strong fluorescent property under UV light (365 nm), and we were interested in its photic properties. The phytochemical study of these alkaloidal extracts of Q. amara led to the isolation of a new fluorescent compound 1 together with 11 known compounds. The structure of compound 1 was elucidated by HRMS and ^1H and ^<13>C NMR techniques including 2D NMR. Compound 1 showed strong fluorescence under UV light. The UV-visible absorption and fluorescence spectra of 1 in various solvents were measured; we found that it exhibited similar behavior of luminous absorption at 520 nm as that at each excitation wavelength of 450, 470, and 490 nm. Hoechst 33342 was added into the cell suspension of living HeLa cells; compound 1 was then added into the suspension. After 1 h, Hoechst, FITC and phase-contrast images were obtained using a confocal laser scanning microscope. Only the cell cytoplasm in living cells stained bright green with compound 1. The rate at which the HeLa cells took up compound 1 was determined by using flow cytometry; the results showed that 97- % of the HeLa cells were stained.
