PSII inhibitory activity of resorcinolic lipids from Sorghum bicolor.
Resorcinolic lipids were isolated from the root extracts of Sorghum bicolor and identified as 4,6-dimethoxy-2-[(8'Z,11'Z)-8',11',14'-pentadecatriene]resorcinol (4), 4-methoxy-6-ethoxy-2-[(8'Z,11'Z)-8',11',14'-pentadecatriene]resorcinol (5), and 4-hydroxy-6-ethoxy-2-[(10'Z,13'Z)-10',13',16'-heptadecatriene]resorcinol (6). Compounds 4 and 5 inhibited photosynthetic oxygen evolution (IC50 0.09 and 0.20 microM, respectively). Compound 4 could not be enzymatically converted to a quinone, suggesting that the quinone moiety is not required for its photosystem II inhibitory activity. Compounds 5 and 6 are reported for the first time.