Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

Abstract

SummaryThe 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.

Light-Triggered Click Chemistry

“…Over the years, a large number of copper catalysts including CuCl 2 ·2H 2 O/sodium benzoate, copper­(II)­(tris­(2-aminoethyl)-amine) ketoprofenate, , copper­(II)­( N , N ′-dimethyl­ethylendiamine) ketoprofenate, copper­(II)­phenyl-2,4,6-trimethylbenzoyl­phosphinate, and others , have been successfully used in light-triggered CuAAC click reactions. To avoid photodecomposition under UV light exposure, numerous visible light-triggered CuAAC reactions were reported. − …”

Gram scale production of 1-azido-β-d-glucose via enzyme catalysis for the synthesis of 1,2,3-triazole-glucosides

“…11,12 1-Azido-b-D-glucose (1) has been used in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction for the construction of triazole-glucosides. [13][14][15][16] Triazoleglucosides exhibit a wide range of glucosidase, [17][18][19] glycogen phosphorylase, [20][21][22] and carbonic anhydrase 23,24 inhibitory activities (Fig. 1).…”

Bismesitoylphosphinic Acid (BAPO‐OH): A Ligand for Copper Complexes and Four‐Electron Photoreductant for the Preparation of Copper Nanomaterials

“…[12] Some additional photoinitiators were have also been applied for the Cu II /Cu I photoreduction. [14] Herein we report the first well-defined and structurally characterized copper complexes with the photoinitiator bismesitoylphosphinic acid (1;B APO-OH) as al igand. [14] Herein we report the first well-defined and structurally characterized copper complexes with the photoinitiator bismesitoylphosphinic acid (1;B APO-OH) as al igand.…”

“…[10b, 11d,13] Furthermore,afew other copper(II) complexes were reported, and upon irradiation with light were converted into copper(I) compounds. [14] Herein we report the first well-defined and structurally characterized copper complexes with the photoinitiator bismesitoylphosphinic acid (1;B APO-OH) as al igand. [15] Remarkably, 1 serves as af our-electron-reducing agent and allows preparation of copper nanomaterials with high yields in aqueous systems.…”