Glutathione transferase: new model for glutathione activation

Glutathione transferases are enzymes of the cellular detoxification system that metabolize a vast spectrum of xenobiotic and endobiotic toxic compounds. They are homodimers or heterodimers and each monomer has an active center composed of a G-site in which glutathione (GSH) binds and an H-site for the electrophilic substrate. When GSH binds to the G-site, the pKa value of its thiol group drops by 2.5 units; this promotes its deprotonation and, therefore, produces a strong nucleophilic thiolate that is able to react with the electrophilic substrate. The mechanism behind the deprotonation of the thiol group is still unknown. Some studies point to the fact that the GSH glutamyl alpha-carboxylate group is essential for GSH activation, whereas others indicate the importance of the active-center water molecules. On the basis of QM/MM calculations, we propose a mechanism of GSH activation in which a water molecule, acting as a bridge, is able to assist in the transfer of the proton from the GSH thiol group to the GSH glutamyl alpha-carboxylate group, after an initial GSH conformational rearrangement. We calculated the potential of mean force of this GSH structural rearrangement that would be necessary for the approach of both groups and we then performed a QM/MM ONIOM scan of water-assisted proton transfer. The overall free-energy barrier for the process is consistent with experimental studies of the enzyme kinetics.     

Highly enantioselective addition of ketones to nitroolefins catalyzed by new thiourea-amine bifunctional organocatalysts

A new and effective organocatalytic system: primary amine derived chiral thiourea catalyst and AcOH-H2O additive, which converts different ketones to gamma-nitroketones in high yields (82-99%) and enantioselectivities (90-99%) has been described.     

Native silica nanoparticle catalyzed anti-Markovnikov addition of thiols to inactivated alkenes and alkynes: a new route to linear and vinyl thioethers

A new route for the synthesis of linear and vinyl thioethers has been demonstrated using bare silica nanoparticle as catalyst at room temperature under solvent-free conditions. The catalyst can be reused up to six times without loss of catalytic activity.     

Highly enantioselective addition of phenylacetylene to aldehydes catalyzed by a camphorsulfonamide ligand

The asymmetric addition of phenylacetylene to aldehydes was carried out by using a camphorsulfonamide titanium complex as a catalyst. The reactions proceeded under mild conditions and gave the products with good yields and high ees. This system is very useful for the synthesis of chiral propargylic alcohol. [reaction: see text]     

Thiophosphoramide catalyzed asymmetric Michael addition of cyclopentanone to chalcones

Thiophosphoramide 1b was found to be an effective bifunctional organocatalyst in the asymmetric Michael reaction of cyclopentanone to various chalcones, affording the corresponding adducts in satisfactory yields with moderate to excellent diastereo- (up to 90/10 dr) and enantioselectivities (up to 92% ee).     

Copper salt catalyzed addition of arylboronic acids to azodicarboxylates

The addition of arylboronic acids 1 to azodicarboxylates 2 in the presence of a catalytic amount of a copper salt under mild reaction conditions gives aryl-substituted hydrazines 3 in high yields. The reaction is tolerant of a wide variety of functional groups.     

Dodecacarbonyltriruthenium catalyzed one-to-one addition of N-substituted formamide to olefins

Dodecacarbonyltriruthenium (Ru₃(CO)₁₂) showed high catalytic activity for the first one-to-one addition of N-substituted formamides to both terminal and internal olefins at 180-200°C under a carbon monoxide pressure of 20 kg cm⁻². The addition of N-metylformamide to cyclopentene afforded N-methylcyclopentanecarboxamide in 90% yield.     

Potassium tert-butoxide catalyzed addition of carbonyl derivatives to styrenes

A catalytic amount of t-BuOK in DMSO allows the addition of ketones or imines to styrenes at 40 degrees C in good to excellent yield. Nitriles add to styrenes in NMP or in DMSO at room temperature.     

Lewis base catalyzed addition of trimethylsilyl cyanide to aldehydes

A variety of achiral Lewis bases were found to catalyze the addition of TMSCN to the aldehydes. Among them, phosphines and amines were the most efficient catalysts. In addition, several chiral amines and phosphines were examined in a catalytic, asymmetric addition of TMSCN to benzaldehyde albeit with low enantioselectivity. A mechanistic study revealed that the reaction was first order in aldehyde, first order in Lewis base, and zeroth order in TMSCN, suggesting the complex formation of TMSCN and Lewis base formation of complex i. However, there are at least two possible scenarios for this catalytic process, and in view of the low selectivities observed, it is not clear which mechanism is operative.     

Asymmetric addition of diethylzinc to aldehydes catalyzed by a camphor-derived β-amino alcohol

The asymmetric addition of diethylzinc to aromatic and aliphatic aldehydes, including linear aliphatic ones, catalyzed by 2 mol % of β-amino alcohol (1S, 2R)-7,7-dimethyl-1-morpholin-4-yl-bicyclo[2.2.1]heptan-2-ol 10 gave the corresponding secondary alcohols in high yields and with up to 94% ee at ambient temperature after 15 min.     

Efficient addition reaction of bromonitromethane to aldehydes catalyzed by NaI: a new route to 1-bromo-1-nitroalkan-2-ols under very mild conditions

[Structure: see text] A catalytic NaI-mediated novel synthesis of 1-bromo-1-nitroalkan-2-ols was carried out by reaction of bromonitromethane with a variety of aldehydes, under very mild conditions. When the reaction was performed with chiral N,N-dibenzyl alaninal, the corresponding enantiopure (1S,2S,3S)-3-dibenzylamino-1-bromo-1-nitrobutan-2-ol was obtained with good stereoselectivity. The structure of this enantiopure bromohydrin was established by X-ray analysis.     

Thiophosphoramide catalyzed asymmetric Michael addition of acetone to functionalized nitrostyrenes: a convenient approach to optically active tetrahydropyrans

Thiophosphoramide 5d was found to be an effective organocatalyst for the enantioselective Michael reaction of problematic acetone to various hydroxymethyl nitrostyrenes, affording the multisubstituted tetrahydropyrans with three stereogenic centers. The Michael addition products generated were obtained as a single diastereomer with enantioselectivities ranging from 46% to 74% ee.     

Lewis acid catalyzed benzylic C-H bond functionalization of azaarenes: addition to enones

A Lewis acid catalyzed benzylic C-H bond functionalization of alkyl-substituted azaarenes is described. Sc(OTf)(3) and Y(OTf)(3) promoted the direct addition of alkyl-substituted azaarenes and benzoxazole to enones and an α,β-unsaturated N-acylpyrrole. Products were obtained in 60-96% yield.     

Rhodium-benzimidazolidin-2-ylidene catalyzed addition of arylboronic acids to aldehydes

Six rhodium–carbene complexes (2a–f) have been prepared and the new compounds characterized by C, H, N analyses, ¹H-n.m.r. and ¹³C-n.m.r. Phenylboronic acid reacts with aldehydes in the presence of a catalytic amount of rhodium(I)–carbene complex, RhCl(COD)(1,3-dialkylbenzimidazolidin-2-ylidene), (2a–f), to give the corresponding aryl secondary alcohols in good yields.     

Lewis acid catalyzed addition of 2,2,2-trifluorodiazoethane to unactivated aldehydes

Condensations of 2,2,2-trifluorodiazoethane with pentanal, cyclohexancarboxaldehyde and benzaldehyde have been performed in presence of antimony pentachloride or boron trifiuoride. These reactions lead mainly to homologated aldehydes or ketones α substituted by a trifluoromethyl group.     

DABCO catalyzed addition of selenosulfonates to alpha,beta-unsaturated ketones

In the presence of DABCO (30 mol%), the addition of various selenosulfonates to alpha,beta-unsaturated ketones proceeded smoothly to give the corresponding adducts in good yields under mild conditions.     

BINOL catalyzed enantioselective addition of titanium phenylacetylide to aromatic ketones

An enantioselective addition of titanium phenylacetylide to ketones, promoted by BINOL, is described; this new enantioselective protocol gives high enantiomeric excess (up to 90% ee) with aromatic ketones using a simple procedure without pyrophoric or expensive reagents.     

Enantioselective Michael addition of aldehydes to nitroolefins catalyzed by pyrrolidine-HOBt

The oxytriazole catalyst “pyrrolidine-HOBt” developed for asymmetric Michael addition of cyclohexanone to nitroolefins is now evaluated for the asymmetric Michael addition of aldehydes to nitroolefins under similar reaction conditions. The results of this study indicate that, the oxytriazole catalyst “pyrrolidine-HOBt” is equally effective in promoting the Michael addition of aldehydes to nitroolefins on employing benzoic acid as an additive. The desired products, γ-nitrocarbonyl compounds were obtained in good yields and high enantioselectivities.