PHOTOSYSTEM-II INHIBITION BY PYRAN-ENAMINE DERIVATIVES

Through the studies on structure-activity relationships of 5-acyl-3-(1 -aminoalkylidene)-4-hydroxy-2 H-pyran-2,6(3 H)-dione derivatives in ph otosystem II (PS II) inhibition, overall lipophilicity of the molecule was found to be a major determinant for the activity. In the substitu ted N-benzyl derivatives, not only the lipophilicity but also the elec tronic and steric characters of the substituents greatly affected the activity. Their mode of PS II inhibition seemed to be similar to that of DCMU, whereas pyran-enamine derivatives needed to be highly lipophi lic to block the electron transport in thylakoid membranes, which in t urn diminished the permeability through biomembranes.