A series of (C^S)-cyclometallated Au(III) cationic complexes of general formula [Au(dppta)(dtc)], [Au(dppta)(azmtd)] and [Au(dppta)(azc)Cl] (dppta = N,N-diisopropyl-P,P-diphenylphosphinothioic amide-κC,S; dtc = dithiocarbamate-κS,S'; azc = azolium-2-dithiocarboxylate-κS; azmdt = azol(in)ium-2-(methoxy)methanedithiol-κS,S') were synthetized and tested against a panel of bacterial strains belonging to different Gram-positive and Gram-negative species of the ESKAPE group of pathogens. Among the tested compounds, complex 4c had the higher Therapeutic Index (TI) against multidrug resistant strains of S. aureus, S.
View Article and Find Full Text PDFA novel lipoformulation was developed by encapsulating cationic (S^C)-cyclometallated gold(III) complex [Au(dppta)(NPy-PZ-dtc)] (AuPyPZ) in liposomes. The liposomal form of compound AuPyPZ has a bactericidal action similar to that of the free drug without any appreciable effect on the viability of mammalian cells. Furthermore, the nanoformulation reduces metalloantibiotic-induced inhibition of hERG and the inhibition of cytochromes, significantly decreasing the potential liabilities of the metallodrug.
View Article and Find Full Text PDFA series of cyclometallated gold(III) complexes 21-27 of general formula [Au(dppta)(azdtc)Cl] (dppta = ,-diisopropyl-,-diphenylphosphinothioic amide-κC,S; azdtc = azol(in)ium-2-dithiocarboxylate-κS) were prepared and characterized by spectroscopic and diffractometric techniques. Treatment of [Au(dppta)(azdtc)Cl] complexes with methanol led to their quantitative transformation into a novel family of (C^S, S^S)-cyclometallated gold(III) complexes of general formula [Au(dppta)(azmtd)] (azmdt = azol(in)ium-2-(methoxy)methanedithiol-κS,S) 28-34. All the [Au(dppta)(azdtc)Cl] complexes 21-27 catalyzed the alkylation of indoles, whereas [Au(dppta)(azmtd)] complexes 28-34 were inactive.
View Article and Find Full Text PDFA bienzymatic cascade has been designed and optimized to obtain enantiopure chlorohydrins starting from the corresponding 1-aryl-2-chlorobut-2-en-1-ones. For the synthesis of these α-chloroenones, a two-step sequence was developed consisting of the allylation of the corresponding aldehyde with 3-dichloroprop-1-ene, followed by oxidation and further isomerization. The selective cooperative catalytic system involving ene-reductases (EREDs) and alcohol dehydrogenases (ADHs) afforded the desired optically active chlorohydrins under mild reaction conditions in excellent conversions (up to >99%) and selectivities (up to >99:1 diastereomeric ratio (dr), >99% enantiomeric excess ()).
View Article and Find Full Text PDFThe 1,3-butadiene motif is widely found in many natural products and drug candidates with relevant biological activities. Moreover, dienes are important targets for synthetic chemists, due to their ability to give access to a wide range of functional group transformations, including a broad range of C-C bond-forming processes. Therefore, the stereoselective preparation of dienes have attracted much attention over the past decades, and the search for new synthetic protocols continues unabated.
View Article and Find Full Text PDFIn this work, the first example of a radical stereodivergent reaction directed towards the stereoselective synthesis of both (R*,R*)- and (R*,S*)-2,2'-biflavanones promoted by samarium diiodide is reported. Control experiments showed that the selectivity of this reaction was exclusively controlled by the temperature. It was possible to generate a variety of 2,2'-biflavanones bearing different substitution patterns at the aromatic ring in good-to-quantitative yields, being both stereoisomers of the desired compounds obtained with total or high control of selectivity.
View Article and Find Full Text PDFOne of the main drawbacks in the application of metal-oxide nanoparticles as lubricant additives is their poor stability in organic media, despite the good anti-wear, friction-reducing and high-load capacity properties described for these materials. In this work, we present a novel procedure to chemically cap the surface of ZrO nanoparticles (ZrONPs) with long hydrocarbon chains in order to obtain stable dispersions of ZrONPs in non-aqueous media without disrupting their attributes as lubricant additives. C-8, C-10 and C-16 saturated flexible chains were attached to the ZrONP surface and their physical and chemical characterization was performed by transmission electron microscopy, thermogravimetric analysis, attenuated total reflectance Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and solid-state nuclear magnetic resonance.
View Article and Find Full Text PDFThe combined activity of (S)-proline and an achiral tetraphenylborate TBD-derived guanidinium salt permits the aldol reaction between azidoacetone and aromatic, or heteroaromatic aldehydes. The α-azido-β-hydroxy methyl ketones obtained as products can be isolated in good yield, with high diastereo- and enantioselectivity.
View Article and Find Full Text PDFA novel methodology has been developed to obtain enantiopure 2-C-glycosyl-3-nitrochromenes. First, (Z)-1-bromo-1-nitroalkenes were prepared from the corresponding sugar aldehydes through a sodium iodide-catalyzed Henry reaction with bromonitromethane followed by elimination of the resulting 1-bromo-1-nitroalkan-2-ols. In the next step, reaction of the sugar-derived (Z)-1-bromo-1-nitroalkenes with o-hydroxybenzaldehydes afforded enantiopure (2S,3S,4S)-3-bromo-3,4-dihydro-4-hydroxy-3-nitro-2H-1-benzopyrans, which, upon SmI2-promoted β-elimination, yielded chiral enantiopure 2-C-glycosyl-3-nitrochromenes.
View Article and Find Full Text PDFOxone, a cheap, stable, and nonhazardous oxidizing reagent, transforms α,β-unsaturated ketones of defined stereochemistry into their corresponding vinyl acetates through a Baeyer-Villiger reaction. This process is general and straightforward, tolerating a wide range of functional groups.
View Article and Find Full Text PDFThe choice of the anion of an achiral TBD-derived guanidinium salt, used as cocatalyst for proline, allows reacting cycloketones with aromatic aldehydes and preparing either anti- or syn-aldol adducts with very high enantioselectivity. As a proof of principle, we show how the judicious choice of an additive allows individual access to all possible products, thus controlling the stereochemical outcome of the asymmetric aldol reaction. The origin of the syn diastereoselectivity unfolds from an unusual equilibrium process coupled to the enamine-based catalytic cycle standard for proline.
View Article and Find Full Text PDFThe heterogeneous system TBD/Al(2)O(3) is an efficient catalyst for the intermolecular aldol reaction between ketones and aromatic aldehydes. This system operates with low catalysts loading (10%), in water or organic solvents, and with short reaction times. The desired aldol products are rendered cleanly.
View Article and Find Full Text PDFA chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results.
View Article and Find Full Text PDFThe combined activity of (S)-proline and an achiral cocatalyst (a TBD-derived guanidinium salt) allow direct aldol reactions to be carried out with high diastereoselectivity and enantioselectivity under solvent-free conditions with a rather simple reaction setup where stirring is not required.
View Article and Find Full Text PDFSamarium metal and samarium diiodide have become important tools as selective cyclopropanating agents in organic synthesis due to their high chemo- and stereoselectivity. Therefore, Sm and SmI(2) are the ideal reagents to prepare cyclopropane derivatives. This tutorial review highlights C-C multiple bond cyclopropanation processes promoted by samarium or samarium diiodide.
View Article and Find Full Text PDFA novel, totally regioselective transformation of aromatic N-4-methoxyphenylaziridine 2-carboxamides into 2-aminoamides promoted by active manganese (Mn*) is reported. alpha-Amino ketones can be readily obtained by reaction of morpholine-derived 2-aminoamides with organolithium compounds.
View Article and Find Full Text PDFA method to obtain (Z)-beta,gamma-unsaturated nitriles in high or good yields and with moderate or high stereoselectivity is described. The products were achieved through the photoinduced metalation of 3-acetoxy-4-chloronitriles with SmI2. The starting compounds were readily prepared, and a mechanism is proposed to explain this stereoselective beta-elimination reaction.
View Article and Find Full Text PDFAn efficient and general synthesis of aziridines by the reaction of imines derived from p-toluenesulfonamides with in situ generated iodomethyllithium, with a simple and rapid experimental protocol, is reported for the first time. The reaction with the chiral aldimine derived from phenylalaninal allowed access to (2R,1'S)-2-(1'-aminoalkyl)aziridine with very high diastereoselectivity, in enantiopure form. A mechanism to explain this novel reaction is proposed.
View Article and Find Full Text PDFWhile the organometallic compounds derived from many metals have found a broad application in organic synthesis, the use of organomanganese compounds has only recently been developed due to the passivity exhibited by commercial Mn in the direct metalation of organic compounds. In this Concept article, we highlight the potential of manganese and its organometallic compounds in organic synthesis by illustration of the studies previously reported by others and our laboratory in this field. Based on the transformations reported herein, organomanganese compounds could become important tools in the future of the organic synthesis, due to their high selectivity.
View Article and Find Full Text PDFA Mn*-promoted sequential process directed toward the synthesis of (Z)-alpha-halo-alpha,beta-unsaturated esters or amides is described. In both cases, the process takes place with complete Z-stereoselectivity. In addition, (Z)-alpha-chloro-alpha,beta-unsaturated ketones and carboxylic acids, and (Z)-haloallylic alcohols were readily prepared from (Z)-alpha-halo-alpha,beta-unsaturated amides derived from morpholine, or esters.
View Article and Find Full Text PDFThe transformation of enantiopure (2R,4R)- and (2S,4S)-N,N-dibenzyl-1,2:4,5-diepoxypentan-3-amine, 1 and 2, into the corresponding enantiopure (3S,5S)- and (3R,5R)-3,5-dihydroxy-3-aminopiperidines, 3 and 4 respectively, is described. The opening of the two epoxide rings with a range of amines takes place with total regioselectivity and high yields, in the presence of LiClO4. A mechanism to explain this transformation is proposed.
View Article and Find Full Text PDFAn efficient chromium-promoted alkyl- or silylcyclopropanation of alpha,beta-unsaturated amides is described. These reactions can be carried out on (E)- or (Z)-alpha,beta-enamides in which the C-C double bond is di-, or trisubstituted. This process takes place with total stereospecificity and the new stereogenic center is generated with high or total stereoselectivity.
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