Photosystem II Inhibition by 3-Acyl-5-(l-aminoalkylidene)-4-hydroxy- 2 H-pyran-2,6(3 //)-dione Derivatives

3-Acyl-5-( 1 -am inoalkylidene)-4-hydroxy-2 Hpyran-2,6(3 //)-d ione derivatives carrying lipophilic am ino groups were found to be highly potent inhibitors o f photosynthetic electron transport, and bo th the acyl and the am inoalkylidene groups on the pyran ring appeared to be indispensable for high activity. The structural features needed for activity in the 3-acyl-5(l-am inoalkylidene)-4-hydroxy-2 //-pyran-2 ,6(3 //)-d ione derivatives were very similar to those for 3 -(l-am inoalkylidene)-2//-pyran-2 ,4(3//)-d iones, except for the acyl group in the form er com pounds. Thermoluminescence m easurem ents indicated tha t the 3-acyl-5(l-am inoalky lidene)-4-hydroxy-2 //-pyran-2 ,6(3#)-d ione derivatives bind to the D I protein in a m anner sim ilar to tha t o f D C M U .