Chemical modification of a phenoxyfuranone‐type strigolactone mimic for selective effects on rice tillering or Striga hermonthica seed germination

BACKGROUND We previously reported that a series of phenoxyfuranone compounds, designated ‘debranones’, mimic strigolactone ( SL ) activity. 4‐Bromodebranone ( 4BD ) is a functionally selective SL mimic that reduces the number of shoot branches on rice more potently than GR24 , a typical synthetic SL analogue, but does not induce seed germination in the root‐parasitic plant Striga hermonthica . To enhance the selective activity of debranones in stimulating the seed germination of root‐parasitic plants, we prepared several analogues of 4BD in which the chlorine atom was substituted with an H atom at the o ‐, m ‐ or p ‐position on the phenyl ring (designated 2‐, 3‐, or 4‐chlorodebranone, respectively) or had a bicyclic group instead of the phenyl ring. We evaluated the biological activities of the compounds with rice tillering assays and S. hermonthica seed germination assays. RESULTS Both assays showed that the substituent position affected debranone efficiency, and among the monochlorodebranones, 2‐chlorodebranone was more effective than the other two isomers in both assays. When the activities of the bicyclic debranones were compared in the same two assays, one was more active than GR24 in the rice tillering assay. This debranone also stimulated the germination of S. hermonthica seeds. Thus, some debranone derivatives induced the germination of S. hermonthica seeds, although their activities were still ∼1/20 that of GR24 . CONCLUSION These results strongly suggest that further and rigorous structure–activity relationship studies of the debranones will identify derivatives that more potently stimulate the suicidal germination of S. hermonthica seeds. © 2016 Society of Chemical Industry