PS II inhibitory activity of 2,4-diamino-6-chloro-s-triazines with a chiral sec-butyl and/or .ALPHA.-methylbenzyl group.

The influence of steric factors on the activity of chiral isomers on the A^-a-methylbenzyl and/or NA-sec-bntyl group of the 2,4-diamino-6-chloro-5-triazines as the inhibitor of the Hill reaction was examined.The (5)-isomers for either chiral center were more active than the corresponding (/?)isomers.The A^-(5)-a-methylbenzyl-s-triazine compound, in spite of a change of the substituent of the 7V4-amino group, exhibited considerably high potency; in particular the 7V4-ethyl derivative (19) was the most potent inhibitor toward PSII.The level of optical discrimination of the receptor site for the chiral isomer of the a-methylbenzyl-s-triazines was greater than those for the sec-butyl derivatives, and their rates varied with the change of steric hindrance of the substituent at the other aminogroup.The structure-activity relationship for the s-triazine compounds tested involved the binding direction of the s-triazine inhibitor being determined by the difference in size of the substituent at each amino group.The amino group with a small substituent offerring low steric hindrance is placed in a narrow binding region (N-region) of the receptor site in PSII protein, and the other amino group is placed in a wide region (W-region), the optical discrimination to each region depending on the steric suitability of the other one.The 7V-a-substituted benzyl-2,4-diamino-s-