Photorelease of tyrosine from α-carboxy-6-nitroveratryl (αCNV) derivatives

On Demand Attachment and Detachment of rac-2-Br-DMNPA Tailoring to Facilitate Chemical Protein Synthesis

Herein, we developed a bifunctional reagent rac-2-Br-DMNPA 2 for the late-stage protection of peptide cysteine. Through the identification of its t-Bu ester 1 as a more competent form under ligation conditions, facile N-terminal and side-chain caging for the model peptide and protein were accomplished. Building upon this, a one-pot ligation and photolysis strategy was applied in the synthesis of the mini-protein chlorotoxin. More importantly, we extended the utility of 2 as a bifunctional linker for traceless solid-phase chemical ligation.

Effect of Photocaged Isopropyl β-d-1-thiogalactopyranoside Solubility on the Light Responsiveness of LacI-controlled Expression Systems in Different Bacteria

Photolabile protecting groups play a significant role in controlling biological functions and cellular processes in living cells and tissues, as light offers high spatiotemporal control, is non‐invasive as well as easily tuneable. In the recent past, photo‐responsive inducer molecules such as 6‐nitropiperonyl‐caged IPTG (NP‐cIPTG) have been used as optochemical tools for Lac repressor‐controlled microbial expression systems. To further expand the applicability of the versatile optochemical on‐switch, we have investigated whether the modulation of cIPTG water solubility can improve the light responsiveness of appropriate expression systems in bacteria. To this end, we developed two new cIPTG derivatives with different hydrophobicity and demonstrated both an easy applicability for the light‐mediated control of gene expression and a simple transferability of this optochemical toolbox to the biotechnologically relevant bacteria Pseudomonas putida and Bacillus subtilis. Notably, the more water‐soluble cIPTG derivative proved to be particularly suitable for light‐mediated gene expression in these alternative expression hosts.

Photoactivatable Dopamine and Sulpiride to Explore the Function of Dopaminergic Neurons and Circuits

Kinetic analysis of dopamine receptor activation and inactivation and the study of dopamine-dependent signaling requires precise simulation of the presynaptic release of the neurotransmitter dopamine and tight temporal control over the release of dopamine receptor antagonists. The 8-cyano-7-hydroxyquinolinyl (CyHQ) photoremovable protecting group was conjugated to dopamine and the dopamine receptor antagonist sulpiride to generate "caged" versions of these neuromodulators (CyHQ-O-DA and CyHQ-sulpiride, respectively) that could release their payloads with 365 or 405 nm light or through 2-photon excitation (2PE) at 740 nm. These compounds are stable under physiological conditions in the dark, yet photolyze rapidly and cleanly to yield dopamine or sulpiride and the caging remnant CyHQ-OH. CyHQ-O-DA mediated the light activation of dopamine-1 (D1) receptors on the breast cancer cell line MDA-MB-231 in culture. In mouse brain slice from the substantia nigra pars compacta, localized flash photolysis of CyHQ-O-DA accurately mimicked the natural presynaptic release of dopamine and activation of dopamine-2 (D2) receptors, causing a robust, concentration-dependent, and repeatable G protein-coupled inwardly rectifying potassium channel-mediated outward current in whole-cell voltage clamp recordings that was amplified by cocaine and blocked by sulpiride. Photolysis of CyHQ-sulpiride rapidly blocked synaptic activity, enabling measurement of the unbinding rates of dopamine and quinpirole, a D2 receptor agonist. These tools will enable more detailed study of dopamine receptors, their interactions with other GPCRs, and the physiology of dopamine signaling in the brain.

Competing pathways for photoremovable protecting groups: the effects of solvent, oxygen and encapsulation

Photolysis of p-hydroxyphenacyloxy arenes releases free phenols in good yields governed by their pK_a. At high pK_a, new byproducts (Bvs. A) reveal a change in reaction mechanism.

Synthesis and characterisation of α-carboxynitrobenzyl photocagedl-aspartates for applications in time-resolved structural biology

We report a new synthetic route to a series of α-carboxynitrobenzyl photocaged l-aspartates for application in time-resolved structural biology. The resulting compounds were characterised in terms of UV/Vis absorption properties, aqueous solubility and stability, and photocleavage rates (τ = μs to ms) and quantum yields (φ = 0.05 to 0.14).

We report a new synthetic route to a series of α-carboxynitrobenzyl photocaged l-aspartates for application in time-resolved structural biology.

Photoactivatable, biologically-relevant phenols with sensitivity toward 2-photon excitation

Spatio-temporal release of biologically relevant small molecules provides exquisite control over the activation of receptors and signaling pathways. This can be accomplished via a photochemical reaction that releases the desired small molecule in response to irradiation with light. A series of biologically-relevant signaling molecules (serotonin, octopamine, capsaicin, N-vanillyl-nonanoylamide, estradiol, and tyrosine) that contain a phenol moiety were conjugated to the 8-bromo-7-hydroxyquinolinyl (BHQ) or 8-cyano-7-hydroxyquinolinyl (CyHQ) photoremovable protecting groups (PPGs). The CyHQ caged compounds proved sensitive toward 1PE and 2PE processes with quantum efficiencies of 0.2-0.4 upon irradiation at 365 nm and two-photon action cross sections of 0.15-0.31 GM when irradiated at 740 nm. All but one BHQ caged compound, BHQ-estradiol, were found to be sensitive to photolysis through 1PE and 2PE with quantum efficiencies of 0.30-0.40 and two photon cross sections of 0.40-0.60 GM. Instead of releasing estradiol, BHQ-estradiol underwent debromination.

Masked rhodamine dyes of five principal colors revealed by photolysis of a 2-diazo-1-indanone caging group: synthesis, photophysics, and light microscopy applications

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as "hidden" markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2-diazo-1-indanone group can be irreversibly photoactivated, either by irradiation with UV- or violet light (one-photon process), or by exposure to intense red light (λ∼750 nm; two-photon mode). All dyes possess a very small 2-diazoketone caging group incorporated into the 2-diazo-1-indanone residue with a quaternary carbon atom (C-3) and a spiro-9H-xanthene fragment. Initially they are non-colored (pale yellow), non-fluorescent, and absorb at λ=330-350 nm (molar extinction coefficient (ε)≈10(4)  M(-1)  cm(-1)) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511-633 and 525-653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε=3-8×10(4)  M(-1)  cm(-1) and fluorescence quantum yields (ϕ)=40-85% in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water-soluble caged red-emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino-reactive N-hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375-420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3-6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (ϕ=20-38%). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10-40% of the non-fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a "dark" non-emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super-resolution optical microscopy is exemplified.

Caged naloxone reveals opioid signaling deactivation kinetics

The spatiotemporal dynamics of opioid signaling in the brain remain poorly defined. Photoactivatable opioid ligands provide a means to quantitatively measure these dynamics and their underlying mechanisms in brain tissue. Although activation kinetics can be assessed using caged agonists, deactivation kinetics are obscured by slow clearance of agonist in tissue. To reveal deactivation kinetics of opioid signaling we developed a caged competitive antagonist that can be quickly photoreleased in sufficient concentrations to render agonist dissociation effectively irreversible. Carboxynitroveratryl-naloxone (CNV-NLX), a caged analog of the competitive opioid antagonist NLX, was readily synthesized from commercially available NLX in good yield and found to be devoid of antagonist activity at heterologously expressed opioid receptors. Photolysis in slices of rat locus coeruleus produced a rapid inhibition of the ionic currents evoked by multiple agonists of the μ-opioid receptor (MOR), but not of α-adrenergic receptors, which activate the same pool of ion channels. Using the high-affinity peptide agonist dermorphin, we established conditions under which light-driven deactivation rates are independent of agonist concentration and thus intrinsic to the agonist-receptor complex. Under these conditions, some MOR agonists yielded deactivation rates that are limited by G protein signaling, whereas others appeared limited by agonist dissociation. Therefore, the choice of agonist determines which feature of receptor signaling is unmasked by CNV-NLX photolysis.