Bridge‐Clamp Bis(tetrazine)s with [N]₈ π‐Stacking Interactions and Azido‐s‐Aryl Tetrazines: Two Classes of Doubly Clickable Tetrazines

Abstract

Click chemistry at a tetrazine core is useful for bioorthogonal labeling and crosslinking. Introduced here are two new classes of doubly clickable s‐aryl tetrazines synthesized by Cu‐catalyzed cross‐coupling. Homocoupling of o‐brominated s‐aryl tetrazines leads to bis(tetrazine)s structurally characterized by tetrazine cores arranged face‐to‐face. [N]8 π‐stacking interactions are essential to the conformation. Upon inverse electron demand Diels–Alder (iEDDA) cycloaddition, the bis(tetrazine)s produce a unique staple structure. The o‐azidation of s‐aryl tetrazines introduces a second proximal intermolecular clickable function that leads to double click chemistry opportunities. The stepwise introduction of fluorophores and then iEDDA cycloaddition, including bioconjugation to antibodies, was achieved on this class of tetrazines. This method extends to (thio)etherification, phosphination, trifluoromethylation and the introduction of various bioactive nitrogen‐based heterocycles.

Coordination Chemistry of a bis(tetrazine) tweezer: A Case of Host-guest Behavior With Silver Salts

“…Bis(tetrazine) 3 and its functionalized derivatives display in the solid state a centroid-to-centroid separation of the central core ranging between 3.3 to 3.5 Å (Figure 1) [3]. Given this structure, and the presence of eight nitrogen atoms as potential coordinating donors, we were intrigued about the potential coordination properties of this new bridge clamp structure with transition metals.…”

“…General synthetic conditions. The bis(tetrazine) 3 was prepared following our previously reported procedure [3].…”

“…The s-tetrazine (Tz) unit (Figure 1, 1) is the object of high interest in photophysics and biomedical applications, in relation with its electron-poor poly(hetero)aromatic nature that is also amenable to click chemistry [1][2][3]. The diversification of synthetic routes to conceive new tetrazine structures has become very useful to expand current applications [3][4][5][6][7][8][9]. We recently reported a copper-catalyzed homocoupling protocol, which allowed the efficient synthesis of constrained bis(tetrazines) with a unique bridge clamp structure (Fig.…”

“…We recently reported a copper-catalyzed homocoupling protocol, which allowed the efficient synthesis of constrained bis(tetrazines) with a unique bridge clamp structure (Fig. 1, 3) [3]. These compounds have been studied in the solid state by X-ray diffraction (XRD, Fig.…”

Overview of Syntheses and Molecular-Design Strategies for Tetrazine-Based Fluorogenic Probes

“…Considering the super-resolution imaging capabilities of tetrazine-functionalized fluorophores produced via iEDDA reactions, this reaction serves as a molecular tool for fluorescent bioimaging and will provide a better understanding of the dynamic nature of biological systems. Although tetrazine-functionalized fluorophores exhibit promising potential [ 46 , 47 , 48 , 49 ], there are several limitations that must be overcome. For instance, (1) the strained olefin still needs to be washed off before treatment with the tetrazine fluorophore, (2) the electrophilic nature of tetrazine renders it unstable (depending on its substituents) against nucleophiles, and (3) the hydrophobic nature of tetrazine increases the possibility of it partaking in non-specific binding.…”