Fast and Bioorthogonal Release of Isocyanates in Living Cells from Iminosydnones and Cycloalkynes

Sydnthiones are versatile bioorthogonal hydrogen sulfide donors

Hydrogen sulfide (H2S) is an important endogenous gasotransmitter, but the bioorthogonal reaction triggered H2S donors are still rare. Here we show one type of bioorthogonal H2S donors, sydnthiones (1,2,3-oxadiazol-3-ium-5-thiolate derivatives), which was designed with the aid of density functional theory (DFT) calculations. The reactions between sydnthiones and strained alkynes provide a platform for controllable, tunable and mitochondria-targeted release of H2S. We investigate the reactivity of sydnthiones‒dibenzoazacyclooctyne (DIBAC) reactions and their orthogonality with two other bioorthogonal cycloaddition pairs: tetrazine‒norbornene (Nor) and tetrazine‒monohydroxylated cyclooctyne (MOHO). By taking advantage of these mutually orthogonal reactions, we can realize selective labeling or drug release. Furthermore, we explore the role of H2S, which is released from the sydnthione-DIBAC reaction, on doxorubicin-induced cytotoxicity. The results demonstrate that the viability of H9c2 cells can be significantly improved by pretreating with sydnthione 1b and DIBAC for 6 h prior to exposure to Dox.

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

Photoclick and Release for Spatiotemporally Localized Theranostics of Single Cells via In Situ Generation of 1,3-Diaryl-1H-benzo[f]indazole-4,9-dione

Bioorthogonal click-release chemistry is a cutting-edge tool for exploring and manipulating biomolecule functions in native biological systems. However, it is challenging to achieve the precise regulation or therapy of individual cells via click-release strategies driven by proximity and thermodynamics. Herein, we propose a novel photoclick-release approach based on a photo-induced cycloaddition between 4,4'-bis(N-arylsydnone) or C-bithienyl-diarylsydnone and 2-arylamino-naphthoquinone via irradiation with 405 or 485 nm light. It constructs 1,3-diaryl-1H-benzo[f]indazole-4,9-dione (BIZON) as a pharmacophore while releases an arylamine for fluorescence turn-on probing. Both photoclick reagents were tailored by connecting to the triphenyl phosphonium delivery motif for enrichment in the mitochondria of live cells. This enables an intracellular photoclick and release under the control of 405 or 485 nm light. We then discovered that the in situ photo-generated BIZON is capable of photosensitizing upon 485 or 520 nm light to produce singlet oxygen inside the mitochondria under aerobic conditions. Therefore, we realized wash-free fluorescence tracking and subsequent anti-cancer efficacy at single-cell resolution using global illumination, which provides a foundation for wavelength-gated single-cell theranostics.

Mutually Orthogonal Bioorthogonal Reactions: Selective Chemistries for Labeling Multiple Biomolecules Simultaneously

Bioorthogonal click chemistry has played a transformative role in many research fields, including chemistry, biology, and medicine. Click reactions are crucial to produce increasingly complex bioconjugates, to visualize and manipulate biomolecules in living systems and for various applications in bioengineering and drug delivery. As biological (model) systems grow more complex, researchers have an increasing need for using multiple orthogonal click reactions simultaneously. In this review, we will introduce the most common bioorthogonal reactions and discuss their orthogonal use on the basis of their mechanism and electronic or steric tuning. We provide an overview of strategies to create reaction orthogonality and show recent examples of mutual orthogonal chemistry used for simultaneous biomolecule labeling. We end by discussing some considerations for the type of chemistry needed for labeling biomolecules in a system of choice.

Click Chemistry: Reaction Rates and Their Suitability for Biomedical Applications

Click chemistry has become a commonly used synthetic method due to the simplicity, efficiency, and high selectivity of this class of chemical reactions. Since their initial discovery, further click chemistry methods have been identified and added to the toolbox of click chemistry reactions for biomedical applications. However, selecting the most suitable reaction for a specific application is often challenging, as multiple factors must be considered, including selectivity, reactivity, biocompatibility, and stability. Thus, this review provides an overview of the benefits and limitations of well-established click chemistry reactions with a particular focus on the importance of considering reaction rates, an often overlooked criterion with little available guidance. The importance of understanding each click chemistry reaction beyond simply the reaction speed is discussed comprehensively with reference to recent biomedical research which utilized click chemistry. This review aims to provide a practical resource for researchers to guide the selection of click chemistry classes for different biomedical applications.

Kinetics of Strain-Promoted Alkyne-Nitrone Cycloadditions (SPANC) with Unprotected Carbohydrate Scaffolded Nitrones

The use of unprotected carbohydrate-derived nitrones as partners in strain-promoted alkyne-nitrone cycloadditions was investigated as a new tool for bioconjugation. The observed second-order reactions displayed rate constants of 3.4 × 10-4-5.8 × 10-2 M-1 s-1, which is the common order of magnitude of reaction kinetics with other simple aliphatic or aromatic nitrones. Applicability of this method to aqueous media was demonstrated by performing a one-pot protocol, which combines sequential formation of the nitrone and cycloaddition with cyclooctyne in water.

Synthesis of sydnonimines from sydnones and their use for bioorthogonal release of isocyanates in cells

In this article, we report the synthesis of sydnonimines from sydnones and their use as dipoles for fast click-and-release reactions. The process relies on nucleophilic aromatic substitution of aliphatic and aromatic amines with triflated sydnones. This new methodology allowed the preparation of functionalised sydnonimine probes that are otherwise difficult to prepare. These probes were then used to release a drug and a fluorescent aromatic isocyanate inside living cells.

Exploration of the Copper-Catalyzed Sydnone and Sydnonimine-Alkyne Cycloaddition Reactions by High-Throughput Experimentation

The reactivity of sydnones and sydnonimines toward terminal alkynes under copper catalysis has been explored using High-Throughput-Experimentation. A large panel of ligands and reaction conditions have been tested to optimize the copper-catalyzed sydnone click reaction discovered by our group ten years ago. This screening approach led to the identification of new ligands, which boosted the catalytic properties of copper and allowed the discovery of a new copper-catalyzed click-and-release reaction involving sydnonimines. This reaction allowed chemoselective ligation of terminal alkynes with sydnonimines and, simultaneously, the release of an isocyanate fragment molecule that can be used for further transformations.

A Bioorthogonal Decaging Chemistry of N-Oxide and Silylborane for Prodrug Activation both In Vitro and In Vivo

Bioorthogonal decaging chemistry with both fast kinetics and high efficiency is highly demanded for in vivo applications but remains very sporadic. Herein, we describe a new bioorthogonal decaging chemistry between N-oxide and silylborane. A simple replacement of "C" in boronic acid with "Si" was able to substantially accelerate the N-oxide decaging kinetics by 106 fold (k2: up to 103 M-1 s-1). Moreover, a new N-oxide-masked self-immolative spacer was developed for the traceless release of various payloads upon clicking with silylborane with fast kinetics and high efficiency (>90%). Impressively, one such N-oxide-based self-assembled bioorthogonal nano-prodrug in combination with silylborane led to significantly enhanced tumor suppression effects as compared to the parent drug in a 4T1 mouse breast tumor model. In aggregate, this new bioorthogonal click-and-release chemistry is featured with fast kinetics and high efficiency and is perceived to find widespread applications in chemical biology and drug delivery.