title: Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst.
abstract: The search for copper catalysts able to perform effectively click reactions in water in the absence of sodium ascorbate is an active area of current research with strong potential for applications in bioconjugation. The water-soluble and photoreducible copper(II)-EDA (EDA = ethylenediamine) complex 1, which has two 4-benzoylbenzoates acting as both counterion and photosensitizer, has been synthesized and characterized by different techniques including single crystal X-ray diffraction. Highly efficient photoreduction was demonstrated when solutions of 1 in hydrogen atom donating solvents, such as THF or MeOH, were exposed to UVA radiation (350-400 nm) provided by a low pressure mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight. In water, a much poorer hydrogen atom donating solvent, the photoreduction of 1 proved inefficient. Interestingly, EPR studies revealed that complex 1 could nonetheless be effectively photoreduced in water when alkynes were present in solution. The catalytic activity of 1 for click reactions involving a range of water-soluble alkynes and azides, in particular saccharides, was tested under various illumination conditions. Complex 1 was found to exhibit a photolatent character, the photogenerated copper(I) being very reactive. On irradiating aqueous reaction mixtures containing 1 mol % of 1 at 365 nm (TLC lamp) for 1 h, click reactions were shown to proceed to full conversion.
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 Crs de la Libération, 33405 Talence, France.
authors.forename: Redouane
authors.initials: R
authors.lastname: Beniazza
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 Crs de la Libération, 33405 Talence, France.
authors.forename: Natalia
authors.initials: N
authors.lastname: Bayo
authors.affiliation: Univ. Grenoble Alpes, DCM UMR-CNRS 5250, F-38000 Grenoble, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Molton
authors.affiliation: Univ. Grenoble Alpes, DCM UMR-CNRS 5250, F-38000 Grenoble, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc
authors.affiliation: Univ. Bordeaux, IECB, UMS 3033/US 001, 2 rue Escarpit, 33607 Pessac, France ; CNRS, IECB, UMS 3033, 33600 Pessac, France ; INSERM, IECB, US 001, 33600 Pessac, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Massip
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 Crs de la Libération, 33405 Talence, France.
authors.forename: Nathan
authors.initials: N
authors.lastname: McClenaghan
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 Crs de la Libération, 33405 Talence, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Lastécouères
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 Crs de la Libération, 33405 Talence, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Vincent
keywords: benzophenone photosensitizer; bioconjugation; click chemistry; copper; photoreduction