Marine Desage-El Murr

Preparation of NHC Borane Complexes by Lewis Base Exchange with Amine- and Phosphine—Boranes

A versatile new method for the preparation of NHC boranes starting from two stable, readily available reactants-an heterocyclic salt and an amine or phosphine-borane-is reported. It uses a Lewis base exchange at boron and provides easy access to new NHC boranes, in particular B-substituted borane ones.

High-throughput evaluation of antioxidant and pro-oxidant activities of polyphenols with thymidine protection assays

A recently reported high‐throughput screening strategy has been applied to the rapid selection of new water‐soluble antioxidants that display strong protective activities. Based on a competitive immunoassay, a triple‐screening procedure was used to evaluate the ability of different compounds to protect thymidine under different oxidative stresses. The pro‐oxidant effect of norbadione A in the presence of iron was observed, while some pulvinic acid derivatives proved strongly protective during γ radiolysis, UV irradiation, and Fenton‐like oxidation.

A Powerful Antiradiation Compound Revealed by a New High-Throughput Screening Method

We present a new high‐throughput screening method for the selection of powerful water‐soluble antiradiation compounds. This method, which uses conventional immunoassay techniques, allowed the capacity of a given compound to protect thymidine from irradiation to be evaluated. By applying this assay to an antioxidant library, we showed for the first time that norbadione A, a well‐known mushroom pigment, has pronounced atypical antiradiation properties.

Tandem CH Activation/Arylation Catalyzed by Low-Valent Iron Complexes with Bisiminopyridine Ligands

Tandem C-H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox-active non-innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first-row transition metals have been shown to involve substrate-based aryl radicals, whereas our catalytic system likely involves ligand-centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner-sphere C-H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble-metal-like behavior could be sustained by the redox-active non-innocent bisiminopyridine ligands.

Metal‐Promoted Coupling Reactions Implying Ligand‐Based Redox Changes

Coupling reactions are staples in the synthetic world and their efficiency relies on well‐defined, mostly bis‐electronic, elementary catalytic steps. An area of great interest currently lies in the taming of radical species and their efficient introduction in catalytic cycles. Among these species bearing radical character, redox‐active ligands hold much potential and can be used to sustain synthetically relevant couplings by introducing ligand‐based electronic contribution. This minireview aims at presenting the current state of this promising field.

C−N Bond Formation from a Masked High‐Valent Copper Complex Stabilized by Redox Non‐Innocent Ligands

The reactivity of a stable copper(II) complex bearing fully oxidized iminobenzoquinone redox ligands towards nucleophiles is described. In sharp contrast with its genuine low-valent counterpart bearing reduced ligands, this complex performs high-yielding C-N bond formations. Mechanistic studies suggest that this behavior could stem from a mechanism akin to reductive elimination occurring at the metal center but facilitated by the ligand: it is proposed that a masked high oxidation state of the metal can be stabilized as a lower copper(II) oxidation state by the redox ligands without forfeiting its ability to behave as a high-valent copper(III) center. These observations are substantiated by a combination of advanced EPR spectroscopy techniques with DFT studies. This work sheds light on the potential of redox ligands as promoters of unusual reactivities at metal centers and illustrates the concept of masked high-valent metallic species.

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox-Active Ligands

Nickel complexes have gained sustained attention as efficient catalysts in cross-coupling reactions and co-catalysts in dual systems due to their ability to react with radical species. Central to this reactivity is nickels propensity to shuttle through several accessible redox states from Ni0 to NiIV . Here, we report the catalytic generation of trifluoromethyl radicals from a nickel complex bearing redox-active iminosemiquinone ligands. This unprecedented reactivity is enabled through ligand-based oxidation performing electron transfer to an electrophilic CF3+ source while the nickel oxidation state is preserved. Additionally, extension of this reactivity to a copper complex bearing a single redox equivalent is reported, thus providing a unified reactivity scheme. These results open new pathways in radical chemistry with redox-active ligands.

Evaluation of the Radioprotective Potential of the Polyphenol Norbadione A

There is an obvious need to develop efficient countermeasure agents for use in emergency situations or as adjuncts to radiotherapy to protect healthy tissues from the consequences of an irradiation. To this end, we have investigated the capacity of norbadione A, a polyphenol extracted from the edible mushroom Bay boletus to reduce the toxicity of ionizing radiation towards cultured cells and whole-body exposed mice. Results indicate that this compound could slightly enhance the resistance of TK6 lymphoid cells to radiation and increase the survival rate in lethally irradiated mice. However, norbadione A was found to be cytotoxic at concentrations over 30 &μυ;M in vitro. The acute toxicity of this compound also precluded its use at higher doses for enhanced in vivo radioprotection. Norbadione A may nevertheless serve as lead for development of less toxic analogs with potentially cytoprotective/ radioprotective activities.