EPR and photophysical characterization of six bioactive oxidovanadium(IV) complexes in the conditions of in vitro cell tests.

A number of oxidovanadium(IV) complexes have been reported to display anticancer activity. A theranostic approach, based on the simultaneous observation of both the effect of oxidovanadium(IV) complexes on cell viability and the disclosure of their intracellular fate, is possible by using oxidovanadium(IV) complexes functionalized with fluorescent ligands. In the present study we accomplished the characterization of six oxidovanadium(IV) complexes in conditions close to those employed for in vitro administration. In particular, we investigated the light harvesting properties of such complexes in the presence of a dimethylsulphoxide/aqueous buffer mixture, and we found that one complex exhibits a quantum yield suitable for confocal microscopy investigations. EPR investigations in the same conditions provide information about the presence of ligands' substitution processes. Finally, the electrochemical properties of all complexes were determined by cyclic voltammetry. The overall results show that these complexes exhibit an average stability in solution; EPR data confirm that DMSO enter the first coordination sphere of oxidovanadium(IV) and suggest the occurrence of partial ligand substitution in the dimethylsulphoxide/aqueous buffer mixture.

Copper-free Sandmeyer cyanation of arenediazonium o-benzenedisulfonimides.

Arene and heteroarenediazonium o-benzenedisulfonimides can be used as efficient reagents in Sandmeyer cyanation. This work reports such reactions carried out by us under very mild conditions using tetrabutyl ammonium cyanide as a safe cyanide source and, interestingly, without the need for a Cu catalyst. The reactions have given rise to aryl nitriles in good yields (25 examples, average yield 75%). A good amount of o-benzenedisulfonimide was recovered from each reaction and then reused to prepare other salts. Mechanistic insights have allowed us to highlight the fundamental role of the o-benzenedisulfonimide anion as an electron transfer agent.

Synthesis of bench-stable diarylmethylium tetrafluoroborates.

A representative number of bench-stable nonsymmetric diarylcarbenium tetrafluoroborates have been isolated via the direct coupling of aryl (or heteroaryl) aldehydes and N-heteroarenes and fully characterized. They have proven to be highly stable in the presence of both EDG and EWG substituents. An (E)-iminium vinylogous substructure has been shown as the common cation scaffold by X-ray analysis and by NOE determination.

Chiral derivatives of 1,2-benzenedisulfonimide as efficient Brønsted acid catalysts in the Strecker reaction.

Two chiral derivatives of 1,2-benzenedisulfonimide, namely 4-methyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide and 4,5-dimethyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide, have been easily synthesized in good overall yields (respectively 34% and 41%) by means of an eleven-step synthetic protocol from commercially available 2-methyl-6-nitroaniline or 2,3-dimethyl-6-nitroaniline. 4,5-Dimethyl-3,6-bis(1-naphthyl)-1,2-benzenedisulfonimide was also synthesized, but the overall yield from 2,3-dimethyl-6-nitroaniline was lower (9%). The atropisomers of these compounds have been resolved and (-)atropisomers have been demonstrated to be efficient chiral catalysts in the Strecker reaction.

Synthesis, characterization and cell viability test of six vanadyl complexes with acetylacetonate derivatives.

Vanadium compounds are known to display a number of therapeutic effects, namely insulin-mimetic and cardiovascular effects. Evidence of the antiproliferative and proapoptotic activity of a number of vanadyl complexes, together with their low toxicity, establishes these metal compounds as promising antitumoral therapeutic agents. In the present work, we describe the synthesis and full characterization of six new vanadyl complexes with acetylacetonate derivatives bearing asymmetric substitutions on the ß-dicarbonyl moiety: the complexes were characterized in the solid state as well as in solution. Our results show that all complexes are in square pyramidal geometry; cis isomers in the equatorial plane are favored in the presence of strongly coordinating solvents. EPR evidence suggests that all complexes are in the bis-chelate form, although in two cases the mono-chelated complex seems to be present as well. Preliminary tests carried out on non-tumor and tumor cell lines show that these complexes are effective in suppressing cell viability and elicit a distinct response of tumor and non-tumor cells.

Preparation and characterization of aryl or heteroaryl(3-indolyl)methylium o-benzenedisulfonimides.

An initial study has been accomplished into the synthetic feasibility of the preparation of diarylcarbenium salt via the direct coupling of aryl (or heteroaryl) aldehydes and arenes (or heteroaryl analogues) in the presence of a strong organic Brønsted acid. A number of stabilized aryl or heteroaryl(3-indolyl)carbenium ions, never previously prepared in the solid state, have been isolated in excellent yields as highly stable o-benzenedisulfonimide salts and have been fully characterized. Their purity has been proven by spectroscopic methods and chemical reduction with NaBH(4). An X-ray crystal structure analysis has been performed on one of the products: an azafulvenium species was shown to be the exclusive structure in the solid state.

o-Benzenedisulfonimide and its chiral derivative as Brønsted acids catalysts for one-pot three-component Strecker reaction. Synthetic and mechanistic aspects.

o-Benzenedisulfonimide (OBS) has efficiently catalysed the one-pot three-component reaction of ketones and aromatic amines with trimethylsilyl cyanide (TMSCN) giving the corresponding α-amino nitriles in excellent yields (23 examples; average yield 85%). Reaction conditions were very simple, green and efficient. Theoretical calculations have allowed us to explain the mechanism of this reaction which has been found to take place in two phases; the first consists of the nucleophilic addition of the aniline to the ketone and the subsequent dehydration to an imine; the second one consists of the formal addition of cyanide anion to the protonated imine. OBS acts in all steps of this mechanism. Without an acid catalyst, the reaction mechanism is more simple but barriers are sensibly higher. A chiral derivative of OBS was also used and gave fairly good results.

A new practical synthesis of triaryl and trisindolylmethanes under solvent-free reaction conditions.

An efficient and practical synthesis of triaryl and trisindolylmethanes is reported via the bisarylation of aryl aldehydes with activated arenes. The new method features mild solvent-free reaction conditions, in most cases nearly stoichiometric reagent ratios, catalytic amount of the readily available, easily-handled, recoverable and reusable Brønsted acid catalyst o-benzenedisulfonimide.

An environmentally friendly Mukaiyama aldol reaction catalyzed by a strong Brønsted acid in solvent-free conditions.

o-Benzenedisulfonimide, a new strong bench-stable Brønsted acid, has been shown to efficiently catalyze the Mukaiyama aldol reaction of aldehydes or dimethyl acetals with silyl enol ethers under mild solvent-free reaction conditions.