Fluorescent-fipronil: Design and synthesis of a stable conjugate

Fipronil is a phenyl pyrazole molecule widely used across the world as both insecticide and veterinary drug. The main goal of this work was to synthesize a fluorescently labeled fipronil derivative for cellular imaging without affecting its intrinsic properties. We selected fluorescein as fluorescent probe and we investigated different strategies for stable chemical ligation between both entities, such as thiourea and direct peptide bond. While thiourea bond displayed low stability, direct peptide bond was difficult to achieve due to problems of steric hindrance. The best result was obtained by conjugation using click chemistry, which allowed to obtain fipronil stably labeled with the fluorescent probe.