Weed infestations cause considerable crop yield losses worldwide. C4 weeds like Black-Grass Cleavers Green foxtail Kochia and Barnyard Grass reduce yields of important C3 cereals such as rice wheat barley and oat. For example Barnyard Grass the most important weed species in rice which is now found in over 60 countries ranging from North America to South Asia provokes yield losses of up to 70 %. Similarly Black-Grass has become a severe threat for global food production causing yield losses of 5 to 50 % already in Western Europe. Besides the resistance to existing herbicides is increasing - provoking the need for alternative weed killers. Selective herbicides against C4 plants would be of outmost importance for the agribusiness and a major turning point in the control of the worst weeds in the world. Scientists of the Heinrich Heine University Duesseldorf succeeded in finding a sophisticated way to sustainably and selectively inhibit C4 type phosphoenolpyruvate (PEP) carboxylase an enzyme that has an important role in CO2 fixation and exists in all variants of C4 metabolism. In contrast to existing approaches the small molecules regarding the present invention do not bind to C3 type PEP carboxylases although these enzymes show sequence identity of up to 95% with the C4 enzyme. Hence they do not affect the C3 metabolism. Consequently C3 plants prosper well C4 plants do not.