Boronic acids facilitate rapid oxime condensations at neutral pH† †Dedicated to Andreas Pfaltz on the occasion of his retirement. ‡ ‡Electronic supplementary information (ESI) available: Detailed kinetic data, HPLC assays, and characterization data for all new compounds are provided. See DOI: 10.1039/c5sc00921a Click here for additional data file.

We report here the discovery and development of boron-assisted oxime formation as a powerful connective reaction for chemical biology. Oximes proximal to boronic acids form in neutral aqueous buffer with rate constants of more than 10 M 1 s , the largest to date for any oxime condensation. Boron's dynamic coordination chemistry confers an adaptability that seems to aid a number of elementary steps in the oxime condensation. In addition to applications in bioconjugation, the emerging importance of boronic acids in chemical biology as carbohydrate receptors or peroxide probes, and the growing list of drugs and drug candidates containing boronic acids suggest many potential applications.