Novel Anthracene Derivatives Isolated from Rice Hulls of Oryza sativa and Their Growth Inhibitory Activity of Radish Seed

Three new compounds orizaanthracenol (1-methoxyanthracen-2-ol, 1), 1-hydroxy-7-((2S,3R,4R,5S)-2'',3'',4''-trihydroxy-5''-(hydroxymethyl)tetrahydro-2H-pyran-1-yloxy)anthracen- 2-yl 3',7'-dimethyloctanoate (2) and 1-hydroxy-7-((2S,3R,4R,5S)-2'',3'',4''-trihydroxy-5''-(hydroxymethyl)tetrahydro-2H-pyran-1-yloxy)anthracen- 2-yl 3',7',11',15',19'-pentamethyltricosanoate (3) have been isolated and determined from the rice hulls of Oryza sativa. The structures of the compounds were elucidated using 1D and 2D NMR spectral methods, viz: 1H-NMR, 13C-NMR, DEPT, COSY and HSQC, and HMBC aided by IR, EIMS and FAB-MS. These isolated compounds were tested in bioassay on germination of radish to detect their inhibitory activities, in which compound 1 exhibited the most inhibition at the concentration of 40 ppm was 50.96% of total dry weight. Furthermore, germination and growth of radish were reduced by 27 to 48%, and dry weight of shoot and root were arranged from 50 to 52%, whilst compounds 2 and 3 exhibited weak inhibition than 1.