Abstract
1. Mode of action
It was suggested that the mode of action of 5-alkylthio-6-chloro-pyrimidine derivatives was inhibition of the Hill reaction. Some of them showed activity higher than atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5 triazine) which had a high inhibitory activity on the Hill reaction. I50 values of these compounds were in the range of 10-7 to 10-8 M. The SPEARMAN'S rank correlation coefficient between herbicidal activity and inhibitory activity on the Hill reaction was calculated. Rs was found to be 0.85 (n=24). It was thus suggested that the herbicidal activity was closely related to the inhibitory activity on the Hill reaction.
2. Structure-activity relationship
In the 4-postion of the pyrimidine ring, the amino substituent was very imporant for the inhibition on the Hill reaction. In the 2-position, the substituent of the low F value showed a good inhibitory activity. SPEARMAN'S rank correlation coefficient (Rs) was found to be 0.88 (n=13) between the SWAIN-LUPTON constant F values of substituent in 2-position and herbicidal activities. The effect of the carbon number in 5-alkylthio substituent was affected by 2-alkylamino substituent.
3. Selectivities
Wheat, barley and malting barley treated with DATP (compound No. 1: 6-chloro-2, 4-diamino-5-methylthiopyrimidine) and compound No. 3 (4-amino-6-chloro-2-ethylamino-5-methylthiopyrimidine) showed a tendency to recover from photosynthesis inhibition after only a day. Barley at the young stage was the most strongly inhibited at first, but the recovery was faster than at an older stage. It was suggested that these cereals might have a detoxication mechanism.
