Specialized Metabolites From the Husks of Rice Oryza sativa L. and Their Biological Activities

Abstract Rice ( Oryza sativa L.) husk harbors a substantial proportion of biological metabolites, as one of the most plentiful agriculture by‐products in rice milling process, rice husk remains poorly utilized. As a continuing search for potential bioactive molecules from the husk of rice, a totally of twelve components ( 1 – 12 ), including six sterol ferulates ( 1 – 6 ), one flavonoid ( 7 ), one dipeptide ( 8 ), and four phenylpropanoid derivatives ( 9 – 12 ) were obtained. All the chemical structures were elucidated based on comprehensive spectroscopic data. Wherein, compounds 1 and 2 were yield as previous undescribed metabolites, and the comprehensive NMR data for compounds 3 and 4 were first presented in its entirety. Motivated by the similarity of the structural motifs of components 1 – 6 to that of reported sterol ferulates, the antioxidant and anti‐inflammatory effects for compounds 1 – 6 were evaluated in vitro. Among them, compounds 5 / 6 had a significant antioxidant activity compare to that of vitamin E in both DPPH and reducing power assay up to the concentration 40 μg/ml; while compounds 1 and 2 exhibited weak suppressive effect on the production of nitric oxide, with the IC 50 values of 53.27±1.37 μM.