Nematicidal quinone derivatives from three Rubia plants

Five new quinone derivatives, rubiasins D-F (1–3), rubialatones A and B (4 and 5), have been isolated from the roots and rhizomes of three Rubia species, Rubia alata, R. wallichiana and R. schumanniana, together with 26 known quinones (6–31). Their structures have been elucidated on the basis of NMR, MS spectra and computational methods. The compounds have been evaluated for their toxicity to the saprophytic nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. Compounds 1, 6 and 7 showed toxicity to C. elegans with the LC₅₀ values at 8.50, 9.44 and 44.82?μg/mL, respectively; and 6 showed toxicity to M. incognita with the LC₅₀ value at 35.22?μg/mL. Meanwhile, compounds 1 and 6 showed inhibitory effect on egg hatch of C. elegans with the LC₅₀ values at 5.60 and 48.95?μg/mL.