Intracellular Synthesis of Indoles Enabled by Visible-Light Photocatalysis

Subcellular Photocatalysis Enables Tumor-Targeted Inhibition of Thioredoxin Reductase I by Organogold(I) Complexes

Selective inhibition of TrxR1 over TrxR2 is a highly sought-after goal, because the two enzymes play distinct roles in cancer progression. However, achieving targeted inhibition is challenging due to their high homology and identical active site sequence. Herein we report a new subcellular photocatalysis approach for targeted inhibition by controllably activating organogold(I) prodrugs within the cytosol, the exclusive location of TrxR1. The NHC-Au(I)-alkynyl complexes are stable and evenly distributed in the cell; they can meanwhile be efficiently transformed into active NHC-Au(I)-L species (L = labile ligands) via a radical mechanism by photocatalysts released into the cytosol (from endosome/lysosome) upon light irradiation, leading to selective inhibition of TrxR1 without affecting TrxR2. This results in strong cytotoxicity to cancer cells with much higher selectivity than auranofin, a pan TrxR inhibitor that cannot discriminate TrxR1/2, along with potent antitumor activities in multiple zebrafish and mouse models. This subcellular prodrug activation may thus suggest a novel approach to precision targeting using the remarkable spatial control of photocatalysis.

Red-shifted photoredox generation and trapping of alkyl radicals towards bioorthogonality

The photocatalytic generation and trapping of alkyl radicals is a powerful synthetic tool in organic chemistry, but it remains underexplored in biological settings. Here, we present two photoredox systems that leverage green- or red-light irradiation for the activation and subsequent Giese coupling of redox-active alkyl phthalimide esters. Besides utilizing mild low-energy light sources, these reactions operate with biocompatible BnNAH or NADH as electron donor. Notably, they display compatibility with air, water and biologically relevant conditions, including cell-culture media or even cell lysates. This work marks a significant step towards integrating synthetic alkyl-radical chemistry into biological settings.

Seeing in the Future - a Perspective on Combining Light with Chemical Biology Approaches to Treat Retinal Pathologies

New concepts to treat eye diseases have emerged that elegantly combine unnatural light exposure with chemical biology approaches to achieve superior cellular specificity and, as a result, improvement of visual function. Historically, light exposure without further molecular eye treatment has offered limited success including photocoagulation to halt pathological blood vessel growth or low light exposure to stimulate retinal cell viability. To add cellular specificity to such treatments, researchers have introduced various biological or chemical light-sensing molecules and combined those with light exposure. (Pre-)clinical trials describe the use of optogenetics and channelrhodpsins, i. e. light-sensitive ion channels, in patient vision restoration. In the chemical arena, pharmacological agents, rendered light-sensitive by reversible modification with photosensitive protecting compounds ("caging"), have been applied to eyes of living mice to photo-release specific cellular activities. Among these were successful proof-of-principle experiments that were conducted to establish photo-sensitive gene therapies in the eye. For light-mediated treatment in combination with chemical biology, we wish to describe here the current frontiers of research in vision restoration with an eye on differences between biological and chemical light-sensing molecules, patient requirements, and future outlooks.

Metal-Mediated Protein Engineering within Live Cells

Metal mediated several organic reactions are known which can be used inside the cellular medium for protein modifications, eventually for targeting diseases. Indeed, due to their ease of handling, rapid solubility, and effective cell penetration, metals are superior than any other competitor as a stimulus/mediator in organic reactions relevant with protein modifications. Metal mediated most effective reactions as a chemical biology tool are Cu(I)-catalyzed azide-alkyne cycloaddition(CuAAC)/click reactions or Pd mediated multiple chemical reactions for intra/extra cellular protein modifications etc. A few examples of Au(III), Ru(III) are also known. Among these, the click reaction has high potential for the management of biomolecules within cells, and thus this methodology is adopted broadly in chemistry, biology towards therapeutic applications in pharmacology. Fast kinetics in aqueous medium at ambient to normal temperature with specificity between precursors (e. g., azide and alkyne for click reactions which are bio-orthogonal to cells) are essential aspects behind the success of metal mediated intracellular reactions. This review dealt with specifically metal mediated protein modifications within live cells, the achievements and challenges.

Noncytotoxic catalytic enzyme functional mimics including cyanide poisoning antidotes

Functional mimics of enzymes have a long history with bioinorganic chemists. Early motivation for creating these mimics was strongly based on the study of the enzyme reaction mechanisms. In more recent times, interest in functional mimics has expanded to catalytic metallodrugs, where the mimics are deliberately designed for specific catalytic reactions intended for therapeutic purposes. In vivo, noncytotoxic catalysis targets reactions designed to activate prodrugs. Natural or de novo proteins were developed for artificial enzyme catalysis of Diels-Alder reactions, or as artificial oxygenase mimics. Novel sulfur-rich catalytic superoxide dismutase (SOD) mimics were discovered as antioxidants. Detoxification of elevated levels of cyanide where the natural rhodanese enzyme becomes inefficient in turnover rates and bioavailability is particularly attractive for sulfur-rich molybdenum clusters. This brief overview includes metal catalysts performing abiotic reactions in vivo disguised by attachment to cell surfaces, as artificial enzymes, and interesting new sulfur-rich complexes performing SOD reactions or neutralizing cyanide.

Ultrafast Charge Transfer on Ru-Cu Atomic Units for Enhanced Photocatalytic H2O2 Production

Photosensitizer-assisted photocatalytic systems offer a solution to overcome the limitations of inherent light harvesting capabilities in catalysts. However, achieving efficient charge transfer between the dissociative photosensitizer and catalyst poses a significant challenge. Incorporating photosensitive components into reactive centers to establish well-defined charge transfer channels is expected to effectively address this issue. Herein, the electrostatic-driven self-assembly method is utilized to integrate photosensitizers into metal-organic frameworks, constructing atomically Ru-Cu bi-functional units to promote efficient local electron migration. Within this newly constructed system, the [Ru(bpy)2]2+ component and Cu site serve as photosensitive and catalytic active centers for photocarrier generation and H2O2 production, respectively, and their integration significantly reduces the barriers to charge transfer. Ultrafast spectroscopy and in situ characterization unveil accelerated directional charge transfer over Ru-Cu units, presenting orders of magnitude improvement over dissociative photosensitizer systems. As a result, a 37.2-fold enhancement of the H2O2 generation rate (570.9 µmol g-1 h-1) over that of dissociative photosensitizer system (15.3 µmol g-1 h-1) is achieved. This work presents a promising strategy for integrating atomic-scale photosensitive and catalytic active centers to achieve ultrafast photocarrier transfer and enhanced photocatalytic performance.

Click-and-Release Formation of Urea Bonds in Living Cells Enabled by Micelle Nanoreactors

The development of innovative strategies enabling chemical reactions in living systems is of great interest for exploring and manipulating biological processes. Herein, we present a pioneering approach based on both bioorthogonal and confined chemistry for intracellular drug synthesis. Exploiting a click-to-release reaction, we engineered nanoparticles capable of synthesizing drugs within cellular environments through bioorthogonal reactions with cyclooctynes. Proof of concept experiments showed that this new approach could be successfully applied to the synthesis of the FDA-approved Sorafenib within cancer cells. The integration of bioorthogonal and confined chemistry not only offers exciting prospects for advancing therapeutic strategies but also opens up new avenues for exploring non-natural reactions within living systems. This innovative approach represents a fundamental extension of the biorthogonal chemistry concept and holds great promise for pioneering developments in therapeutic applications.

Bioorthogonal Synthetic Chemistry Enabled by Visible-Light Photocatalysis

The field of bioorthogonal chemistry has revolutionized our ability to interrogate and manipulate biological systems at the molecular level. However, the range of chemical reactions that can operate efficiently in biological environments without interfering with the native cellular machinery, remains limited. In this context, the rapidly growing area of photocatalysis offers a promising avenue for developing new type of bioorthogonal tools. The inherent mildness, tunability, chemoselectivity, and external controllability of photocatalytic transformations make them particularly well-suited for applications in biological and living systems. This minireview summarizes recent advances in bioorthogonal photocatalytic technologies, with a particular focus on their potential to enable the selective generation of designed products within biologically relevant or living settings.

Prodrug activation by 4,4'-bipyridine-mediated aromatic nitro reduction

Unleashing prodrugs through nitro-reduction is a promising strategy in cancer treatment. In this study, we present a unique bioorthogonal reaction for aromatic nitro reduction, mediated by 4,4'-bipyridine. The reaction is a rare example of organocatalyst-mediated bioorthogonal reaction. This bioorthogonal reaction demonstrates broad substrate scope and proceeds at low micromolar concentrations under biocompatible conditions. Our mechanistic study reveals that water is essential for the reaction to proceed at biorelevant substrate concentrations. We illustrate the utility of our reaction for controlled prodrug activation in mammalian cells, bacteria, and mouse models. Furthermore, a nitro-reduction-annulation cascade is developed for the synthesis of indole derivatives in living cells.

Electrochemical C-H Azidation and Diazidation of Anilines for the Synthesis of Aryl Azides and Diazides

The increasing importance and need in many aspects have driven the rapid development of synthetic studies toward aryl azides. In this paper, electrochemical C-H azidation and diazidation of anilines have been developed using TMSN3 as an azide source. A range of functional groups can be tolerated under the optimized reaction conditions.

Recent advances in electrochemically enabled construction of indoles from non-indole-based substrates

Indole motifs are important heterocycles found in natural products, pharmaceuticals, agricultural chemicals, and materials. Although there are well-established classical name reactions for indole synthesis, these transformations often require harsh reaction conditions, have a limited substrate scope, and exhibit poor regioselectivity. As a result, organic synthesis chemists have been exploring efficient and practical methods, leading to numerous strategies for synthesizing a variety of functionalized indoles. In recent years, electrochemistry has emerged as an environmentally friendly and sustainable synthetic tool, with widespread applications in organic synthesis. This technology allows for elegant synthetic routes to be developed for the construction of indoles under external oxidant-free conditions. This feature article specifically focuses on recent advancements in indole synthesis from non-indole-based substrates, as well as the mechanisms underlying these transformations.

Triplet-Triplet Annihilation Upconversion-Based Photolysis: Applications in Photopharmacology

The emerging field of photopharmacology is a promising chemobiological methodology for optical control of drug activities that could ultimately solve the off-target toxicity outside the disease location of many drugs for the treatment of a given pathology. The use of photolytic reactions looks very attractive for a light-activated drug release but requires to develop photolytic reactions sensitive to red or near-infrared light excitation for better tissue penetration. This review will present the concepts of triplet-triplet annihilation upconversion-based photolysis and their recent in vivo applications for light-induced drug delivery using photoactivatable nanoparticles.