Steroidal constituents of rice (Oryzo sativa) hulls with algicidal and herbicidal activity against blue-green algae and duckweed

Two new compounds, 14-methyl stigmast-9(11)-en-3 alpha-ol-3 beta-D-glucopyranoside (1) and cholest-11-en-3 beta, 6 beta, 7 alpha, 22 beta-tetraol-24-one-3 beta-palmitoleate (2), along with the known compound beta-sitosteryl-3 beta-D-glucopyranosyl-6'-linoleiate (3), were isolated from the methanolic extract of rice (Oryza sativa) hulls. The structures of the two new compounds were elucidated using one- and two-dimensional NMR in combination with IR, EI/MS, FAB/MS, HR-EI/MS and HR-FAB/MS. In bioassays with blue-green algae, Microcystis aeruginosa UTEX 2388 and duckweed, Lemna pciticicostata Hegelm 381, the efficacy of bioactivity of the two new compounds linearly increased as the concentration increased from 0.3 to 300 pm. Compared with momilactone A, compounds 1 and 2 showed similar and higher inhibitory activities against the growth of M. aeruginosa at a concentration of 300 Pm. However, compound 2 was similar to momilactone A in inhibiting L. paucicostata growth at. a concentration of 300 pm. As a result, compound 2 appears to have a strong potential for the environmentally friendly control of weed and algae that are harmful to water-logged rice. Copyright (c) 2006 John Wiley & Sons, Ltd.