Binuclear copper(II) complexes discriminating epimeric glycosides and α- and β-glycosidic bonds in aqueous solution

Abstract

Two chiral binuclear copper(II) complexes were synthesized and characterized for the first time as efficient chemoselective catalysts for the hydrolysis of aryl glycosides and disaccharides in aqueous solution at near neutral pH. Under these conditions, discrimination of epimeric aryl α-glycopyranosides was observed both by 29-fold different reaction rates and 3-fold different proficiency of the catalyst. Additionally, large differentiation of the nature of α- and β- glycosidic bond in aryl glycosides as model compounds is apparent, but also noted in selected disaccharides. The influence of the chirality of the complexes and the role of the configuration of the carbohydrate upon interaction with the catalyst is discussed in detail. Lastly, a putative mechanism for the metal complex-catalyzed hydrolysis is derived from the experimental evidence pointing at deprotonation of the hydroxyl group at C-2 as a pre-requisite for glycoside hydrolysis.

Discrimination of chiral copper(ii) complexes upon binding of galactonoamidine ligands

“…42 Further investigations focused on the preparation of chiral analogs of 2, namely S-Cu 2 (bpdbo), S-(3), and R-Cu 2 (bpdbo), R- (3), that promoted remarkable discrimination of glycosidic bonds and epimeric substrates at near neutral conditions in aqueous solution (Chart 2). 43…”

“…CD spectra were recorded on a Jasco J-1500 CD Spectrometer Model 150 with EXOS liquid cooling system from Koolance Inc. with the supplied Spectra Manager software Version 2.12.00 using a Fisher Scientific Suprasil quartz microcell with 500 µL capacity, 45 mm height and an optical path length l of 10 mm at 10.00 ± 0.01°C. UV-vis 43 were prepared as described; metal-free sodium hydroxide at 99.999% purity, and CHES, TAPS and CAPS buffer at ACS reagent grade quality were purchased from Sigma-Aldrich and used as received. All buffer solutions were prepared by standard methods at ambient temperature accounting for temperature differences at their intended use.…”

Biomimetic Glycoside Hydrolysis by a Microgel Templated with a Competitive Glycosidase Inhibitor

“…Coordination experiments with various galactonoamidines revealed a Gibbs free energy of binding of −10.3 kcal mol −1 for the 1−5 assembly that translates into a pK a,1−5 of 3.5 using isothermal titration calorimetry. 40 The coordination of 1 involves its deprotonated amidine function, the hydroxyl group at C-2, and a third unspecified site. 44 The experimental data excluded coordination of 1 over the hydroxyl group at C-4 but did not elucidate possibile coordination of the amidine over the hydroxyl groups at C-3 or C-6.…”

“…The coordination of galactonoamidine 1 to binuclear complexes was already evaluated in part and included Cu 2 bpdpo ( 5 ), a nonpolymerizable analogue of 3 (Figure ). − As the two metal complexes are different in the ligand backbone periphery, but not the metal site itself, the coordination of galactonoamidine 1 to both metal complexes is comparable. , Strong chelation of 1 to 5 over three binding sites was observed in aqueous CAPS buffer solution at pH 10.50 and 10 °C. Coordination experiments with various galactonoamidines revealed a Gibbs free energy of binding of −10.3 kcal mol –1 for the 1 – 5 assembly that translates into a p K a, 1 – 5 of 3.5 using isothermal titration calorimetry .…”

Microgel-Catalyzed Hydrolysis of Nonactivated Disaccharides

“…The catalyzed disaccharide hydrolysis was monitored on an HPLC system (Shimadzu) using a carbohydrate-selective Rezex RMN-Na + column (Phenomenex) . The computational analysis was performed with PQSmol on a Dell workstation as reported. ,,,,− …”