REVERSE CHIRAL DISCRIMINATION RELATIONSHIPS BETWEEN THE INHIBITORY ACTIVITY OF 1,3,5-TRIAZINES ON PHOTOSYSTEM-II AND LIGHT-INDEPENDENT ROOT-GROWTH

The dissociation constants (pK(d)) of thylakoid binding and the inhibitory activity values (pI(50)) in the photosystem II (PS II) electron-transfer system of optically active 1,3,5-triazine compounds were measured to clarify the chirality-activity relationships. These relationships were compared with those of chiral alpha-methylbenzylaminocyanoacrylates in PS II electron-transfer inhibition and with those in the root growth assay of Echinochloa crus-galli var. frumentacea Wight. The optically active 1,3,5-triazine compounds competed strongly with [C-14]atrazine at the binding site. The pK(d) values of the (S)-isomers of the chiral alpha-methylbenzyl or sec-butyl moieties were greater than those of the corresponding (R)-isomers and paralleled the pI(50) values of the PS II inhibition assay. There were good correlations between the pK(d) values and the pI(50) values and between eudismic indexes of the enantiomers both for binding and for the PS II system. Relationships between the pK(d) or the pI(50) values of the eutomers, (S)-enantiomers, and the eudismic indexes for the chiral pairs were correlative, and eudismic indexes decreased with increased activities. This relationship was in contrast not only to that of the chiral alpha-methylbenzylaminocyanoacrylates in photosynthetic inhibition but also to that of the chiral 1,3,S-triazine compounds in foot growth inhibition of E. crus-galli var, frumentacea Wight in the dark. (C) 1994 Academic Press, Inc.