Building biomimetic model compounds of dinuclear and trinuclear copper clusters for stereoselective oxidations

Presti, Eliana Lo; Monzani, Enrico; Santagostini, Laura; Casella, Luigi

doi:10.1016/j.ica.2017.09.045

Cited by 13 publications

(13 citation statements)

References 58 publications

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“…and the L66 ‐system of Casella et al . (Scheme ),, , no catalytic monooxygenation activity has been observed with such systems so far. This might be attributed to the fact that coordination of the substrate to the µ‐η 2 :η 2 peroxo complex, which leads to the formation of a “ternary intermediate”, is more difficult if each copper center is coordinated by three instead of two terminal ligands.…”

Section: Introductionmentioning

confidence: 96%

“…Subsequent catalytic systems (Scheme ) devised by Casella et al ., Stack et al ., Ottenwaelder and Lumb et al ., Herres‐Pawlis et al . and others gave rise to new functionalities and provided further mechanistic insight into details of copper‐dioxygen chemistry , . So far our group exclusively used bidentate ligands like, e.g., L py 1 , to emulate the reactivity of tyrosinase (Scheme ) .…”

Section: Introductionmentioning

confidence: 99%

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Employing Linear Tridentate Ligands with Pyrazole End Groups in Catalytic Tyrosinase Model Chemistry: Does Hemilability Matter?

et al. 2019

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Several copper(I) and copper(II) complexes supported by hemilabile bis(pyrazolylmethyl)amine (pzma) ligands are synthesized and structurally characterized. The copper(I) complexes with hexafluoridophosphate or perchlorate anions are employed as catalysts for the tyrosinase‐like oxygenation of 2,4‐di‐tert‐butylphenol (DTBP‐H). Their activities are comparable to that of [Cu(MeCN)2PMP]PF6 (PMP= pyrazolylmethylpyridine) investigated earlier. In contrast to the copper(I) pzma complexes, their congeners supported by non‐hemilabile bis(pyrazolylethyl)amine (pzea) ligands are found to be catalytically inactive.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Employing Linear Tridentate Ligands with Pyrazole End Groups in Catalytic Tyrosinase Model Chemistry: Does Hemilability Matter?

et al. 2019

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“…The kinetic parameters k cat and K M determined for the oxidation of the chiral catechols are collected in Table 1. The discrimination capacity of the copper catalyst against the enantiomeric substrates was evaluated using the stereoselectivity indexes R k cat/KM and R k cat , 14,15,25 expressed as percentages, given by the following equations (with norepinephrine, L refers to the R enantiomer, and D refers to the S enantiomer).…”

Section: Inorganic Chemistrymentioning

confidence: 99%

“…In fact, the complete inversion of R indexes for L-/D-dopaOMe from low to high substrate concentration has no precedent in the large series of studies performed before by our group. 15,25 The interpretation of this unusual behavior is facilitated by the large difference between the K M and k cat values for the two enantiomeric substrates. D-DopaOMe exhibits an affinity for the active species of [Cu 2 (mXHI)] 4+ ∼2 orders of magnitude larger than that of L-dopaOMe, whereas the latter substrate reacts more than six times faster than its D A peculiar feature of the reaction is the increase of reaction rate upon increasing the concentration of acetate buffer, which was studied in detail for L-dopaOMe (Figure S7).…”

Section: Inorganic Chemistrymentioning

confidence: 99%

“…Among tyrosinase biomimetic complexes with chiral ligands reported so far by our group, namely, [Cu 2 (PHI)] 4+ , 20 [Cu 2 (EHI)] 4+ , 25 and [Cu 2( L55Bu 4 )] 4+ , 14 and others, 15 plex [Cu 2 (mXHI)] 4+ exhibits the best discrimination capacity, as assayed in the catecholase reaction, with R index up to 85 for the best substrates, that is, L-and D-dopaOMe. The reason why chiral recognition is displayed with these substrates can be ascribed to the bulkiness of the methyl ester groups, which may force an interaction with the benzyl substituents present on the L-histidyl ligands.…”

Section: ■ Conclusionmentioning

confidence: 99%

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A Stereoselective Tyrosinase Model Compound Derived from an m-Xylyl-l-histidine Ligand

et al. 2019

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The aim of mimicking enzyme activity represents an important motivation for the development of new catalysts. A challenging objective is the development of chiral complexes for bioinspired enantioselective oxidation reactions. Herein, we report a new chiral dinuclear copper(II) complex based on a m-xylyl-bis(histidine) ligand (mXHI) as a biomimetic catalyst for tyrosinase and catechol oxidase. The new ligand improves a previous system also containing two tridentate N3 units derived from l-histidine that were connected by a short, rigid ethanediamine bridge. In mXHI the bridge is provided by the more extended m-xylyl moiety. The dicopper(II) complex [Cu2(mXHI)]4+ was studied as a catalyst for stereoselective oxidations of enantiomeric couples of chiral catechols of biological interest (L/D-dopa, L/D-dopa methyl ester, and (R/S)-norepinephrine), showing excellent discrimination capability, particularly for the methyl esters of dopa enantiomers. The catechol oxidation was studied in acetate buffer as slightly acidic medium, and a role of acetate as bridging ligand between the two coppers, preorganizing the dinuclear center in a more catalytic efficient structure, could be established. The oxidation of β-naphthol and 3,5-ditertbutylphenol was studied as a model monophenolase reaction. The oxidation proceeds stoichiometrically, and the partial incorporation of 18O into β-naphthol when the reaction was performed using 18O2 suggests the existence of two competitive reaction pathways, a genuine monooxygenase mechanism and a radical pathway. However, the more challenging reaction on derivatives of l-/d-tyrosine did not lead to the desired monooxygenase product but only to products of radical oxidation. Complex [Cu2(mXHI)]4+ was also used for the catalytic sulfoxidation of thioanisole in the presence of hydroxylamine as cosubstrate, in a preliminary attempt to model the reaction of external monooxygenases. The reaction proceeds with 25 turnovers, but the enantiomeric excess of sulfoxide was modest.

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Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

et al. 2021

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Coupled dinuclear copper oxygen cores (Cu2O2) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O2 transport and substrate oxidation in many organisms. μ‐1,2‐cis peroxido dicopper cores (CP) have been proposed as key structures in the early stages of O2 binding in these proteins; their reversible isomerization to other Cu2O2 cores are directly relevant to enzyme function. Despite the relevance of such species to type III copper proteins and the broader interest in the properties and reactivity of bimetallic CP cores in biological and synthetic systems, the properties and reactivity of CP Cu2O2 species remain largely unexplored. Herein, we report the reversible interconversion of μ‐1,2‐trans peroxido (TP) and CP dicopper cores. CaII mediates this process by reversible binding at the Cu2O2 core, highlighting the unique capability for metal‐ion binding events to stabilize novel reactive fragments and control O2 activation in biomimetic systems.

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Building biomimetic model compounds of dinuclear and trinuclear copper clusters for stereoselective oxidations

Cited by 13 publications

References 58 publications

Employing Linear Tridentate Ligands with Pyrazole End Groups in Catalytic Tyrosinase Model Chemistry: Does Hemilability Matter?

Employing Linear Tridentate Ligands with Pyrazole End Groups in Catalytic Tyrosinase Model Chemistry: Does Hemilability Matter?

A Stereoselective Tyrosinase Model Compound Derived from an m-Xylyl-l-histidine Ligand

Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

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