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

Background: 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.

Results: 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.

Conclusions: The present work demonstrates that pyrimidine derivatives containing pyrazole can be used as potential lead compounds for developing novel pigment biosynthesis inhibitors.