Constituents from the Stem Wood of Euphorbia quinquecostata with Phorbol Dibutyrate Receptor-Binding Inhibitory Activity

Bioassay-guided fractionation of an EtOAc extract of the stem wood of Euphorbia quinquecostata using a phorbol dibutyrate receptor-binding assay system as a monitor yielded four inhibitory isolates (1-4), inclusive of one new compound, 17-hydroxyingenol 20-hexadecanoate (1), and three previously known compounds, ingenol 20-hexadecanoate (2), ent-16 alpha,17-dihydroxyatisan-3-one (3), and ent-3 beta,16 alpha,17-trihydroxyatisane (4). Also isolated from this extract were 10 constituents inactive in this bioassay, namely, 2,2'-dihydroxy-4,6-dimethoxy-3-methylacetophenone (5), a new structure, and nine known compounds identified as ent-13S-hydroxyatis-16-ene-3, 14-dione; 2-hydroxy-4,6-dimethoxyacetophenone (xanthoxylin); 2-hydroxy-4,6-dimethoxy-3-methylacetophenone; 6-hydroxy-7-methoxycoumarin; lupeol acetate; beta-sitosterol; sitosterol beta-D-glucopyranoside; 6,7,8-trimethoxycoumarin; and 3,3',4'-tri-O-methyl-4-O-[alpha-L-rhamnopyranosyl (1"'-->6")-beta-D-glucopyranosyl]ellagic acid. The structures of compounds 1 and 5 were established by chemical and spectroscopic methods.