Shining light on photo-responsive molecular tools: advances in visible-to-NIR activatable photolabile protecting groups

Abstract

The utilisation of light as an external stimulus to control the structure and function of bio-relevant molecules in healthy and diseased cells and tissues serves as a valuable means to probe fundamental molecular events of complex cellular processes. Indeed, the photocaging approach has proved highly popular, whereby bioactive molecules are modified with photolabile protecting groups, rendering them temporarily inactive. Biological activity is only restored upon irradiation with a defined wavelength of light, resulting in the irreversible cleavage of the caging group. While seminal works are reliant on the use of phototoxic UV light for photoactivation, the rapid evolution of the field of photopharmacology has facilitated the development of more sophisticated caging groups with physiochemical and photophysical properties better suited for in vivo applications. Herein, we highlight the recent progress made on the development of BODIPY-, cyanine- and xanthene-derived caging groups, which utilise visible-to-near-infrared light for photoactivation. The strategies employed to red-shift absorption spectra, as well as improve photolysis efficiencies and aqueous solubility have been of particular interest, and are therefore discussed in detail in this review.