Phloroglucinol Derivatives as Potent Photosystem II Inhibitors

Studies on structure/activity relationships of phloroglucinol derivatives that had been designed based on the structures of grandinol and homograndinol. potent photosystem II (PS II) inhibitors in Eucalyptus grandis, revealed that two electron-withdrawing groups which differ by their electron-withdrawing power on a phloroglucinol nucleus were essential for activity. A larger difference in the electron-withdrawing power between the two groups enhanced the activity, and 3-nitro-phloroglucinecarboxamides and the corresponding thioamides were the most active ones when they had proper lipophilic side chains. Their binding domain seems to overlap with those of DCMU and atrazine, whereas they may approach to the site in a similar manner to that of phenol type inhibitors. Accordingly, the phloroglucinol derivatives represent a new type of PS II inhibitors.