Lasianosides A-E: New Iridoid Glucosides from the Leaves of Lasianthus verticillatus (Lour.) Merr. and Their Antioxidant Activity

The genus (Rubiaceae) consists of approximately 180 species, of which the greatest species diversity is found in tropical Asia. Some of the species have been used in folk medicine to treat tinnitus, arthritis, fever, and bleeding. (Lour.) Merr. (Syn. auct. non Hemsl.) is a shrub, branchlets terete about 1.5-3 m in height. This paper studies the chemical composition of the leaves of for the first time, which resulted in the isolation of five undescribed iridoid glucosides, lasianosides A-E ( - ), together with three known compounds ( - ). The undescribed structures of isolated compounds ( - ) were characterized by physical and spectroscopic data analyses, including one-dimensional (1D) and two-dimensional (2D) NMR, IR, UV, and high-resolution electrospray ionization mass spectra (HR-ESI-MS). Furthermore, the electronic circular dichroism data determined the absolute configurations of the new compounds. The free radical scavenging properties of isolated compounds was assessed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and their cytotoxicity was assessed toward human lung cancer cell line A549 by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Among the isolated compounds, and displayed potent radical scavenging activities with IC values of 30.2 ± 1.8 and 32.0 ± 1.2 µM, which were comparable to that of Trolox (29.2 ± 0.39 µM), respectively, while possessed moderate activity with an IC value of 46.4 ± 2.3 µM. None of the isolated compounds exerted cytotoxicity against human cell line A549. As a result, lasianosides C, D, and E have the potential to be non-toxic safe antioxidant agents.