Characterization of antioxidant alkaloids and phenolic acids from anthocyanin-pigmented rice (Oryza sativa cv. Heugjinjubyeo)

As a part of our study on the analysis of bioactive secondary metabolites, we used bioactivity-guided fractionation and isolation methods to isolate five compounds from the ethylacetate-soluble fraction of the aleurone layer of Oryza sativa cv. Heugjinjubyeo, a highly developed rice cultivar; 4-carboethoxy-6-hydroxy-2-quinolone (1), ethyl-3,4-dihydroxybenzoic acid (2), 4-hydroxy-3-methoxyphenylacetic acid (3), 3,4-dihydroxybenzoic acid (4), and 4-hydroxy-3-methoxy cinnamic acid (5). These compounds showed significant antioxidant activity in a concentration-dependent manner through the scavenging of 1,1-diphenyl-2-picrylhydrazyl radicals. The structure of new compound 1 was elucidated on the basis of spectroscopic evidence, particularly the results obtained via hetero-nuclear multiple-bond connectivity and high-resolution MS spectroscopy.