Tuning Imine and Boronic Acid Reactivity with Neighboring Group Effects: Iminoboronates and Diazaborines in Bioconjugation Chemistry, Sensor Development, and Stimuli-Responsive Materials

Dynamic covalent chemistry (DCC) are reversible reactions at chemical equilibrium. Owing to their reversible dynamics, these reactions represent an expansive toolbox for the development bioconjugation techniques and stimuli responsive materials. Several DCC reactions fit the criteria necessary for bioconjugation chemistry, including the condensation of α-amines with carbonyls to form hydrazones or oximes and the condensation of boronic acids with vicinal diols to form boronate esters. Separately, the chemical features of these reactions offer their own advantages in the development of bioconjugation and stimuli-responsive materials. However, when combined, novel reactivity and applications are unlocked. Iminoboronates are an emerging class of compounds that include an imine in the ortho position relative to an aryl boronic acid, combining the features of arylboronic acid reactivity with that of imine chemistry. In iminoboronates, the reactivity of the arylboronic acid and imine functionalities are dependent on each other, leading to unique behavior of the imine/boronic acid ensemble. Here, we review the applications of iminoboronates in bioconjugation chemistry, including their utilization in the bioconjugation of peptides, the labeling of whole cells, the development of chemical probes, and as key linkages in stimuli-responsive biomaterials.