Photosystem II Inhibition by Pyran-enamine Derivatives

Through the studies on structure-activity relationships o f 5-acyl-3-(l-aminoalkylidene)4-hydroxy-2 H-pyran-2,6(3 H)-dione derivatives in photosystem II (PS II) inhibition, overall lipophilicity o f the molecule was found to be a major determinant for the activity. In the sub­ stituted N-benzyl derivatives, not only the lipophilicity but also the electronic and steric char­ acters o f the substituents greatly affected the activity. Their mode o f PS II inhibition seemed to be similar to that o f D C M U , whereas pyran-enamine derivatives needed to be highly lipophilic to block the electron transport in thylakoid membranes, which in turn diminished the permea­ bility through biomembranes.