Chemical Constituents of Apios americana Tubers and Their Inhibitory Activities on Nitric Oxide Production in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

Apios americana is an important food crop producing edible tubers with high nutritional and medicinal values and is widely cultivated in many countries. Despite its usefulness, research on its secondary metabolites and biological activities has been limited. In the present study, a new coumaronochromone, (2 R,3 S)-3,7,4'-trihydroxy-5-methoxycoumaronochromone (1), and two new isoflavone glucosides, 7,2',4'-trihydroxy-5-methoxyisoflavone-4'- O-β-d-glucopyranoside (3) and 5,7,4'-trihydroxyisoflavone-7- O-β-d-gentiotrioside (5), were isolated from the tubers of A. americana via chromatographic separation. Seventeen known compounds (2, 4, and 6-20) were also obtained from this plant part. The chemical structures of 1, 3, and 5 were determined by the interpretation of spectroscopic data. The absolute structure of the new compound 1 was established from experimental and calculated electronic circular dichroism spectra. This is the first study to determine the absolute configuration of a 3-hydroxycoumaronochromone derivative. The potential anti-inflammatory activity of the 20 isolates obtained was evaluated by measuring their inhibitory effects on nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 macrophages. Among the isolates, seven compounds (1, 3, 6-8, 15, and 20) showed substantial inhibition of nitric oxide production in RAW 264.7 cells, with the most active being compound 1 (IC₅₀ value of 0.38 ± 0.04 μM).