Design and Synthesis of a Calcium‐Sensitive Photocage

Abstract

Photolabile protecting groups (or "photocages") enable precise spatiotemporal control of chemical functionality and facilitate advanced biological experiments.E xtant photocages exhibit as imple input-output relationship,h owever, where application of light elicits ap hotochemical reaction irrespective of the environment. Herein, we refine and extend the concept of photolabile groups,s ynthesizing the first Ca 2+ -sensitive photocage.T his system functions as ac hemical coincidence detector,r eleasing small molecules only in the presence of both light and elevated [Ca 2+ ]. Caging af luorophore with this ion-sensitive moiety yields an "ion integrator" that permanently marks cells undergoing high Ca 2+ flux during an illumination-defined time period. Our general design concept demonstrates an ew class of light-sensitive material for cellular imaging, sensing,a nd targeted molecular delivery.Small molecules that absorb light have broad utility as tools to probe and perturb biological systems.C hemical fluorophores constitute one important type of light-absorbing molecule.[1] Thea bility to modify dyes using chemistry allows the construction of numerous probes for specific applications.F or example,changing the chemical structure of fluorophores can allow fine-tuning of spectral properties. Likewise,c hemical dyes that respond to changes in ion concentration have been prepared. Thed esign and synthesis of such ion indicators involves incorporation of molecular recognition motifs into af luorophore where the reversible binding of as pecific ion alters the absorption and/or fluorescence quantum yield of the dye.T his strategy has produced probes for many biologically relevant ions,i ncluding Na,a nd Zn 2+ ,a llowing noninvasive monitoring of ion concentration inside living cells. [2] Photolabile protecting groups or "photocages" comprise another important class of organic chromophore where photon absorption elicits cleavage of ac hemical bond. [3] Like fluorophores,t he spectral properties of photocages have been manipulated using chemistry,r esulting in photolabile groups with longer wavelengths and larger two-photon cross-sections.[4] However,u nlike fluorescent dyes,t he incorporation of ion-sensitive motifs into photocages is essentially unexplored. Probes built from ion-sensitive photolabile groups could complement reversible ion indicators,functioning as chemical coincidence detectors that would selectively and irreversibly release asmall molecule only in the presence of both light and increased ion concentration. In particular, caging af luorophore with such an ion-sensitive photocage would yield af luorescent ion "snapshot indicator" or "integrator" that would permanently record increased ion concentration during an illumination-defined time period. Integrator systems based on fluorescent proteins [5] and rhodopsins [6] have been described recently,b ut small-molecule ion integrators remain unknown. This currently limits the use of such probes to biological systems that are amenable to genetic man...

A volumetric three-dimensional digital light photoactivatable dye display

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Precise spatiotemporal control of voltage-gated sodium channels by photocaged saxitoxin

“…Photocaged molecules provide unique advantages over traditional pharmacologic agents and pro-drugs, namely precise temporal and spatial release, tunability, and reagent-less deprotection. Neuroactive compounds including GABA 8 , glutamic acid 9,10 , dopamine 11 , serotonin 12 , Leu-enkephalin 13 , cAMP 14 , lipids 15 , and calcium 16 have been photocaged in order to study signaling mechanisms in cells, tissues, and whole organisms. Despite this impressive collection of photo-protected reagents, to our knowledge, no such compound has been designed to directly target action potentials (APs), the fundamental mode of communication in electrically excitable cells.…”

Electronic and Steric Optimization of Fluorogenic Probes for Biomolecular Imaging

“…6 Caged fluorophores (which are also known as photoactivatable fluorophores) are related but are activated instead by illumination at specific wavelengths. 7 …”