New chemical constituents from Oryza sativa straw and their algicidal activities against blue-green algae.

Five new constituents, 5,4'-dihydroxy-7,3'-dimethoxyflavone-4'-O-beta-D-xylopyranosyl-(2a -> 1b)-2a-O-beta-D-xylopyranosyl-(2b -> 1c)-2b-O-beta-D-xylopyranosyl-2c-octadecanoate (1), 5,4'-dihydroxy-7,3'-dimethoxyflavone-4'-O-alpha-D-xylopyranosyl(2a -> 1b)-2a- O-alpha-u-xyl opyran osyl- (2b -> 1c)-2b-O-alpha-D-xylopyranosyl-(2c -> 1c)-2c- O-alpha-D-xylopyranosy1-2d-octadecanoate (2), kaempferol-3-O-alpha-D-xylopyranosyl- (2a -> 1b)-2a-O-alpha-D-xylopyranosyl-(2b -> 1c)-2b-O-alpha-D-xylopyranosyl-(2c -> 1d)-2c-O-alpha-D-xylopyranosy1-2d-hexadecanoate (3), methyl salicylate-2-O-alpha-u-xylopyranosyl-(2a -> 1b)-2a-O-alpha-D-xylopyranosyl-(2b -> 1c)-2b-O-alpha-D-xylopyranosyl-(2c -> 1d) -2c-O-alpha-D-xylopyranosyl-(2d -> 1e)-2c-O-alpha-D-xylopyranosyl-(2e -> 1b)-2a-O-alpha-a-D-xylopyranosyl- (2f -> 1g) 1g)-2f-O-alpha-D-xylopyranosyl-(2g -> 1h)-2g-O-alpha-D-xylopyranosyl-2h-geranilan-8',10'-dioic acid-1'-oate (4), and oleioyl-beta-D-arabinoside (5), along with eight known compounds, were isolated from a methanol extract of Oryza sativa straw. The structures of the new compounds were elucidated using one- and two-dimensional NMR spectroscopies in combination with IR, ESI/MS, and HR-ESI/FTMS. In bioassays with blue-green algae, the efficacies of the algicidal activities of the five new compounds (1-5) were evaluated at concentrations of 1, 10, and 100 mg/L. Compound S had the highest growth inhibition (92.6 +/- 0.3%) for Microcystis aeruginosa UTEX 2388 at a concentration of 100 ppm (mg/L). Compound 5 has high potential for the ecofriendly control of weeds and algae harmful to water-logged rice.