Two-photon fluorescence sensors for imaging NMDA receptors and monitoring release of Zn²⁺ from the presynaptic terminal

Synaptic Zn²⁺ plays an important role in neurotransmission and a neuromodulator. The development of the imaging tools for monitoring spatiotemporal changes taking place in synaptic Zn²⁺ concentrations is necessary in order to understand the role of Zn²⁺ in the function of many aspects of the glutamate system. In this work, two-photon probes 1 and 2, bearing ifenprodil-like tails that have affinity for NMDA receptors of neuronal cells, were designed and prepared. The two-photon fluorescent probe 1, which bears (N-(6-acetylnaphthalen-2-yl)-N-methylglycine) as two-photon fluorophore, enables high resolution imaging of neuronal cells. The two-photon fluorescent probe 2, which contains the di-2-picolylamine (DPA) as a Zn²⁺-binding site, the naphthalimide unit as the two-photon fluorophore, and the ifenprodil-like tail as the NMDA receptor binding moiety, can be employed for selective detection of Zn²⁺ located near the NMDA receptor and for monitoring concentration changes of Zn²⁺ in live neurons and hippocampal tissues.