New N-acyl homoserine lactone analogues, N-acyl-3-amino-5H-furanone derivatives and some 4-halogeno counterparts, were synthesised and tested for their ability to modulate LuxR-dependent bacterial quorumsensing. Both types of analogues proved to be inhibitors, the halogenated compounds being significantly more active. Molecular modelling suggested that the conjugated enamide group induces two preferential