Four new constituents, as 5, 7-dihydroxy-4'-methoxyflavonol-3-O-β-d-arabinopyranosyl-(2''→1''')-O-β-d-arabinopyrnosyl-2'''-O-3'''', 7''''-dimethylnonan-1''''-oate (1), 5-hydroxy-7, 4'-dimethoxyflavone-5-O-α-d-arabinopyranosyl-(2"→1''')-O-α-d-arabinopyranosyl-2'''-O-3'''', 7''''-dimethylnonan-1''''-oate (2), 5-hydroxy-7, 4'-dimethoxyflavone-5-O-β-d-arabinofuranosyl-(2"→1''')-O-β-d-arabinopyranosyl-2'''-O-lanost-5-ene (3) and 4',4''-diferuloxy feruloyl-O-α-d-arabinopyranosyl-(2a→1b)-O-α-d-arabinopyranosyl-(2b→1c)-O-α-d-arabinopyranosyl-(2c→1d)-O-α-d-arabinopyranosyl-(2d→1e)-O-α-d-arabinopyranosyl-2e-3''', 7'''-dimethylnonan-1'''-oate (4), along with three known compounds (5⁻7) were isolated from Oryza sativa leaves and straw. The structures of new and known compounds were elucidated by 1D (¹H and 13C NMR) and 2D NMR spectral methods, viz: COSY, HMBC, and HSQC aided by mass techniques and IR spectroscopy. The cytotoxicity of these constituents was assessed by using (RAW 264.7) mouse macrophage cell line, and allelopathic effects of compounds (1⁻7) on the germination and seedling growth characteristics such as seedling length and root length of barnyardgrass (Echinochloa oryzicola) were evaluated. Significant inhibitory activity was exhibited by compounds comprising flavone derivatives such as (1⁻3) on all of seed germination characteristics. The allelopathic effect of flavone derivatives were more pronounced on seedling length and root length than the germination characteristics. The higher concentration of flavone derivatives showed stronger inhibitory effects, whereas the lower concentrations showed stimulatory effects in some cases.
Keywords: E. oryzicola; Gramineae; Oryza sativa L.; allelopathic activities; cytotoxicity test; new chemical constituents; rice leaves and straw.