A 1H NMR assay for measuring the photostationary States of photoswitchable ligands

A Modular Approach to Arylazo-1,2,3-triazole Photoswitches

Azoheteroarenes make up an emerging class of photoswitchable compounds with unique photophysical properties and advantages over traditional azobenzenes. Therefore, methods for synthesizing azoheteroarenes are highly desirable. Here, we utilize azide-alkyne click chemistry to access arylazo-1,2,3-triazoles, a previously unexplored class of azoheteroarenes that exhibit high thermal stabilities and near-quantitative bidirectional photoconversion. Controlling the catalyst or 1,3-dipole grants access to both regioisomeric arylazotriazoles and arylazoisoxazoles, highlighting the versatility of our approach.

A fine-tuned azobenzene for enhanced photopharmacology in vivo

Despite the power of photopharmacology for interrogating signaling proteins, many photopharmacological systems are limited by their efficiency, speed, or spectral properties. Here, we screen a library of azobenzene photoswitches and identify a urea-substituted "azobenzene-400" core that offers bistable switching between cis and trans with improved kinetics, light sensitivity, and a red-shift. We then focus on the metabotropic glutamate receptors (mGluRs), neuromodulatory receptors that are major pharmacological targets. Synthesis of "BGAG_12,400," a photoswitchable orthogonal, remotely tethered ligand (PORTL), enables highly efficient, rapid optical agonism following conjugation to SNAP-tagged mGluR2 and permits robust optical control of mGluR1 and mGluR5 signaling. We then produce fluorophore-conjugated branched PORTLs to enable dual imaging and manipulation of mGluRs and highlight their power in ex vivo slice and in vivo behavioral experiments in the mouse prefrontal cortex. Finally, we demonstrate the generalizability of our strategy by developing an improved soluble, photoswitchable pore blocker for potassium channels.

Strategies and considerations of G-protein-coupled receptor photopharmacology

G-protein-coupled receptor (GPCR) pharmacology tends to be complex and at times poorly understood. This has led to the development of GPCR-targeting agents that often demonstrate poor pharmacokinetic properties and poor selectivity for their target receptors. One approach that is emerging as a means of addressing these limitations is the use of molecules whose activity can be controlled by light. Photopharmacology involves the incorporation of a photoswitch into the structure of a given compound, cage or linker and following irradiation with light, undergoes a structural rearrangement, which changes its biological activity. The use of light-regulated ligands offers the opportunity to modulate and understand GPCR signaling in a more spatiotemporal manner than classical pharmacological approaches. In this chapter we will discuss some of the advancements that have been made in photopharmacology, particularly in developing photoswitchable ligands that target class A GPCRs, e.g., muscarinic acetylcholine receptors, class B GPCRs, e.g., glucagon-like peptide-1 receptor, and class C GPCRs, e.g., metabotrobic glutamate receptors. Given the intricacy of GPCR pharmacology, this chapter will also discuss some of the challenges the field faces when designing photopharmacological tools. Furthermore, it will propose that it is with a full appreciation of the spectrum of pharmacological and pharmacokinetic properties of photoswitchable ligands that research will be better placed to develop ligands with a reduced risk of failure during preclinical progression. This will likely enable photopharmacological approaches to continue to find novel applications and offer new perspectives in understanding (patho)physiology to ultimately inform future GPCR drug discovery efforts.

A Redox Isomerization Strategy for Accessing Modular Azobenzene Photoswitches with Near Quantitative Bidirectional Photoconversion

Photoswitches capable of accessing two geometric states are highly desirable, especially if their design is modular and incorporates a pharmacophore tethering site. We describe a redox isomerization strategy for synthesizing p-formylazobenzenes from p-nitrobenzyl alcohol. The resulting azo-aldehydes can be readily converted to photoswitchable compounds with excellent photophysical properties using simple hydrazide click chemistry. As a proof of principle, we synthesized a photoswitchable surfactant enabling the photocontrol of an emulsion with exceptionally high spatiotemporal precision.

Light at the end of the channel: optical manipulation of intrinsic neuronal excitability with chemical photoswitches

Ion channels are transmembrane proteins that control the movement of ions across the cell membrane. They are the molecular machines that make neurons excitable by enabling the initiation and propagation of action potentials (APs). Rapid signaling within and between neurons requires complex molecular processes that couple the sensing of membrane voltage or neurotransmitter release to the fast opening and closing of the ion channel gate. Malfunction of an ion channel's sensing or gating module can have disastrous pathological consequences. However, linking molecular changes to the modulation of neural circuits and ultimately to a physiological or pathological state is not a straightforward task. It requires precise and sophisticated methods of controlling the function of ion channels in their native environment. To address this issue we have developed new photochemical tools that enable the remote control of neuronal ion channels with light. Due to its optical nature, our approach permits the manipulation of the nervous system with high spatial, temporal and molecular precision that will help us understand the link between ion channel function and physiology. In addition, this strategy may also be used in the clinic for the direct treatment of some neuronal disorders.