Fig. 1

Chemical structures of the compounds tested; 1, chrysophanol; 2, emodin; 3, 3,6,8-trihydroxy-1-methylanthraquinone-2-carboxylic acid; Me; 4, aloesaponol I; 5, plumbagin; 6, benzoquinones; 2,5-dihydroxy-3-ethyl-2,5-cyclohexadiene-1,4-dione; 7, 2,5-dihydroxy-3-propyl-2,5-cyclohexadiene-1,4-dione; 8, 2,5-dihydroxy-3-butyl-2,5-cyclohexadiene-1,4-dione; 9, 2,5-dihydroxy-3-heptyl-2,5-cyclohexadiene-1,4-dione; 10, homoembelin; 11, rapanone; 12, 2,5-dihydroxy-3-pentadecyl-2,5-cyclohexadiene-1,4-dione; 13, 5-O-methylembelin; 14, 2,5-di-O-dimethylembelin; 15, maesaquinone; 16, 2,5 dimethoxy-6-(14-nonadecenyl)-1,4-benzoquinone; 17, 1,2,4,5-tetraacetate-3-methyl-6-(14-nonadecenyl)-cyclohexadi-2,5-diene; 18, ardisiaquinone; 19, 3′,5′-dihydroxy-1′-methoxychalcone; 20, 1′,5′-dihydroxy-3′-methoxychalcone; 21, 1′,3′-dihydroxy-2′,5′-dimethoxychalcone; 22, 5′-hydroxy-1′,3′-dimethoxychalcone; 23, 1′,3′,5′-trihydroxy-2′-methoxychalcone; 24, 1,5-diacetate-3′-methoxychalcone