Design, synthesis and herbicidal activities of novel 4-(1H -pyrazol-1-yl)-6-(alkynyloxy)-pyrimidine derivatives as potential pigment biosynthesis inhibitors

With the objective of finding novel valuable herbicidal candidates, a series of novel 4-(1H-pyrazol-1-yl)-6-(alkynyloxy)-pyrimidine derivatives were synthesised and their herbicide activities were evaluated in vivo.The results showed that many target compounds expressed bleaching activities. Among these, compound 5 h showed the best bleaching activity to gramineous weeds, being able to produce the highest inhibition of chlorophyll level in seedlings of Pennisetum alopecuroides L. (IC50 = 3.48 mg L(-1) ). Moreover, compound 5 h expressed good selective toxicity between gramineous P. alopecuroides L. and broadleaf plant Brassica campestris L.The present work demonstrates that pyrimidine derivatives containing pyrazole can be used as potential lead compounds for developing novel pigment biosynthesis inhibitors.