Water‐Soluble Triazabutadienes that Release Diazonium Species upon Protonation under Physiologically Relevant Conditions

Abstract

Triazabutadienes are an understudied structural motif that have remarkable reactivity once rendered water-soluble. It is shown that these molecules readily release diazonium species in a pH-dependent manner in a series of buffer solutions with pH ranges similar to those found in cells. Upon further development, we expect that this process will be well suited to cargo-release strategies and organelle-specific bioconjugation reactions. These compounds offer one of the mildest ways of generating diazonium species in aqueous solutions.

A Chemoselective Rapid Azo-Coupling Reaction (CRACR) for Unclickable Bioconjugation

“…Recently, the aryl-trizabutadiene group has been established to be a facile precursor to the aryl-diazonium species, the release of which can be triggered by light or low pH. 16 We synthesized a conjugate (8, Figure 3C) between biotin and a triazabutadiene, which upon brief irradiation releases biotin-4CDz (Figure S16A). We showed selective biotinylation of sfGFP-151-5HTP, but not wild-type sfGFP, upon treatment with biotin-4CDz by a western-blot analysis using a streptavidin-HRP probe (Figure 3E), and MS analysis (Figure S16).…”

One‐Pot Catalytic Synthesis of gem‐Diazides and Their Direct Conversion into Safe Materials

“…The reaction of NHCs with diazides is of high synthetic importance, as depicted in a recent report on their reaction with bis(NHC)s to form polymeric materials having triaza‐1,3‐butadiene linking units . The importance of the triaza‐1,3‐butadiene structural motif was again underlined in a recent communication that showed that such molecules could release diazonium ions in aqueous solutions at a pH‐dependent rate, and this might be utilized in future biochemical strategies . Compound B reported herein has two triaza‐1,3‐butadiene motifs connected by one carbon atom constituting a gem ‐bis(triaza‐1,3‐butadiene) compound, the first of its kind.…”

Light‐Activated Triazabutadienes for the Modification of a Viral Surface

“…Recently we reported that triazabutadienes possess key characteristics that bring us closer to our goals of chemo-selective host-pathogen crosslinking experiments: they release aryl diazonium species in a physiologically relevant range of pH (Figure 1b). [8] As such, this chemical functionality can be viewed as a protecting group for reactive aryl diazonium ions. We also reported that this functionality undergoes a photo-induced isomerization that enables release the aryl diazonium ion at higher pH.…”

“…A pH of 5 was chosen due to its similarity to the pH of the late endosome [18] and our previous studies with triazabutadienes had shown that the aryl diazonium ion should be released within minutes. [8],[19] Expecting liberation of the diazonium and subsequent conjugation to 6 , we were surprised that labeling of BSA was not observed at pH 5 after 2 hours of acidification, (labeling was surprisingly also not observed within the same time frame at pH 3) (see Supporting information, Figure S2). This result was attributed to the hydrophobic nature of the triazabutadiene scaffold that was chosen.…”

“…If buried in the hydrophobic interior of the protein (or a pocket), access of the key N3 nitrogen atom to the aqueous environment could be occluded and thus protonation would be prevented (Figure 2a). [8] If true, we hypothesized that a conformational change of the molecule would re-expose the N3 nitrogen and allow for aryl diazonium ion release. We recognize that this hydrophobic protection has advantages and disadvantages: an advantage is stability to neutral and acid pH; a disadvantage is that light would be required to liberate the aryl diazonium ion.…”