CYCLOHEXANEDIONES AS GOOD TOOLS FOR STUDYING STRUCTURE-ACTIVITY-RELATIONSHIPS IN PHOTOSYNTHETIC ELECTRON-TRANSPORT INHIBITION

Cyclohexanedione derivatives conjugated with an enamine moiety are potent electron transport inhibitors. QSAR analysis of these derivatives substituted at the 4- and/or 5-positions of their cyclohexane ring revealed that the inhibitory potency showed dose correlation with pi values of these substituents. However, derivatives carrying the 3-(4-tolyl)propyl group at the 4-position exhibited higher inhibition than the expected activity due to the lipophilicity of the substituent. This result suggested that parameters other than pi values should be considered when applying QSAR analysis on these series of compounds. In other words, there is probably an interaction between the binding site and 4-tolyl group. In addition, r/s analysis of the binding manner of these derivatives was conducted using four types of D1 mutants. The pattern of r/s values showed an apparent difference in the binding manners between the cyclohexanediones and known herbicides such as DCMU and atrazine. It was inferred that the cyclohexanedione derivatives with the 4-tolyl group interacted with amino acid residues of D1 protein. In this respect, cyclohexanedione derivatives had a different binding manner from that of the classical photosynthetic electron transport inhibitors.