Fluorescent Arylphosphonic Acids: Synergic Interactions between Bone and the Fluorescent Core

Herein, we report the third generation of fluorescent probes (arylphosphonic acids) to target calcifications, particularly hydroxyapatite (HAP). In this study, we use highly conjugated porphyrin‐based arylphosphonic acids and their diesters, namely 5,10,15,20‐tetrakis[m‐(diethoxyphosphoryl)phenyl]porphyrin (m ‐H(8)TPPA‐OEt(8)) and 5,10,15,20‐tetrakis [m‐phenylphosphonic acid]porphyrin (m ‐H(8)TPPA), in comparison with their positional isomers 5,10,15,20‐tetrakis[p‐(diisopropoxyphosphoryl)phenyl]porphyrin (p ‐H(8)TPPA‐iPr(8)) and 5,10,15,20‐tetrakis [p‐phenylphosphonic acid]porphyrin (p ‐H(8)TPPA), which have phosphonic acid units bonded to sp(2) carbon atoms of the fluorescent core. The conjugation of the fluorescent core is thus extended to the (HAP) through sp(2)‐bonded −PO(3)H(2) units, which generates increased fluorescence upon HAP binding. The resulting fluorescent probes are highly sensitive towards the HAP in rat bone sections. The designed probes are readily taken up by cells. Due to the lower reported toxicity of (p ‐H(8)TPPA), these probes could find applications in monitoring bone resorption or adsorption, or imaging vascular or soft tissue calcifications for breast cancer diagnosis etc.