Bioorthogonal conjugation chemistry is an important chemical tool, which facilitates the study of exceptionally complex biological systems. The current landscape of bioorthogonal reactions includes a wide array of chemistries, most of which are sub-optimal for one or more reasons, including slow kinetics, off-target reactivity, generation of toxic side reactions, formation of non-stable products, or the requirement of toxic reagents or catalysts. However, we have discovered that conjugation of a hydrazine-containing small molecule, semcarbazide, to an aryl aldehyde or ketone with an ortho-boronic acid moiety is both fast (&gt;103 M-1s-1) and meets the aforementioned optimal characteristics for biocompatibility. The ortho-boronic acid substituent accelerates diazaborine formation to enable rapid kinetics, and the conjugation reaction is both compatible with and non-toxic towards both blood serum and cell lysates, and shows minimal interference from abundant biomolecules. Upon establishing biocompatibility, it was determined that diazaborine formation can be applied for facile labeling of several important bacterial pathogens via cell wall remodeling with suitably designed unnatural amino acids. Varied bacterial selectivity was observed for these synthetic cell wall modifiers. For example, D-AB3, which presents a 2-acetylphenylboronic acid moiety as its side chain, was found to most efficiently incorporate into E. coli over other bacterial species. Furthermore, we have developed fluorogenic versions of the diazaborine conjugation reaction, which allows fluorescent labeling of bacteria under no-wash conditions, demonstrating the wide adaptability of this facile, bioorthogonal chemistry.

Facile labeling of bacterial pathogens via diazaborine formation of semicarbazide

254th National Meeting (2017)

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