Stereospecific Synthesis of Steroidal 20,16-γ-Carbolactones

Two strategies have been explored for the synthesis of steroidal 20,16-γ-carbolactones from the corresponding 17-ketoandrostane. A highly efficient, stereospecific protocol has been developed for the β-oriented cis-γ-lactone, based on a Michael addition of cyanide to a conjugated ketone. A different approach, involving prior attachment of a 3-carbon side chain on C-17 of a 17-oxo-16β-acetoxy-androstane led to the epimeric, α-oriented lactone.     

A Convenient Method for the Phosphorylation of Phenols with Diethyl Cyanophosphonate

Phosphorylation of phenols with diethyl cyanophosphonate in methylene chloride solution at 0°C is an easy, rapid and good yielding reaction.     

Straightforward Method for the Preparation of Lysine-Based Double-Chained Anionic Surfactants

Double-chained surfactants with potential biocompatibility have been prepared in high yields by lysine acylation with four natural saturated fatty acids (C₆ to C₁₂) and with cis-undec-5-enoic acid. The surfactants were found to assemble into nanotubules in aqueous medium and, when mixed with a commercial cationic surfactant, to spontaneously form liposomes.     

A Recyclable Trinuclear Bifunctional Catalyst Derived from a Tetraoxo Bis‐Zn(salphen) Metalloligand

A tetraoxo bis‐Zn(salphen) supramolecular host can bind various divalent metal salts, thereby providing access to trinuclear bifunctional systems that incorporate both Lewis acid sites and dynamically bound nucleophilic anions. The formation of these trinuclear species was investigated and their stability features were also determined. The application of these trinuclear complexes as bifunctional catalysts was evaluated in the formation of cyclic organic carbonates from epoxides and CO₂. The catalytic data, in combination with control experiments, clearly demonstrate that these trinuclear compounds show much higher recycling potential compared to various control compounds and they can be used in up to five cycles without an observable loss in activity. Furthermore, this new recyclable catalytic system does not require any additives and can be applied under solvent‐free conditions.     

Cyclopalladation and Reactivity of Amino Esters through C?H Bond Activation: Experimental,Kinetic, and Density Functional Theory Mechanistic Studies

The orthopalladation, through C? H bond activation, of a large number of amino esters and amino phosphonates derived from phenylglycine, and having different substituents at the aryl ring and the C‐α atom, as well as on the N‐amine atom, has been studied. The experimental observations indicated an improvement in the yields of the orthopalladated compounds when the N‐amine and/or the C‐α atom are substituted, when compared with the unsubstituted methyl phenylglycinate derivatives. In contrast, substitutions at the aryl ring do not promote significant changes in the orthometalation results. Furthermore, the use of hydrochloride salts of the amino esters has also been shown to have a remarkably favorable effect on the process. All these observations have been fully quantified at different temperatures and pressures by a detailed kinetic study in solution in different solvents and in the presence and absence of added Brønsted acids and chloride anions. The data collected indicate relevant changes in the process depending on these conditions, as expected from the general background known for cyclopalladation reactions. An electronic mechanism of the orthopalladation has been proposed based on DFT calculations at the B3LYP level, and a very good agreement between the trends kinetically measured and the theoretically calculated activation barriers has been obtained. The reactivity of the new orthopalladated amino phosphonate derivatives has been tested and it was found that their halogenation, alkoxylation and carbonylation resulted in formation of the corresponding functionalized ortho‐haloaminophosphonates, ortho‐alkoxyaminophosphonates and oxoisoindolinylphosphonates.     

Pyracene‐Linked Bis‐Imidazolylidene Complexes of Palladium and Some Catalytic Benefits Produced by Bimetallic Catalysts

Two new palladium complexes with a pyracene‐linked bis‐imidazolylidene (pyrabim) group have been obtained and fully characterized. The related monometallic analogues were obtained from the coordination of an acetanaphthene‐supported N‐heterocyclic carbene (NHC). The catalytic properties of all complexes were studied in the acylation of aryl halides with hydrocinnamaldehyde, and in the Suzuki–Miyaura coupling of aryl halides and aryl boronic acids. The results show that the presence of a second metal in the dimetallic complexes induces some benefits in the catalytic behavior of the complexes. This effect is more pronounced in the Suzuki–Miyaura coupling, for which the dimetallic complexes exhibit significantly higher activity than their monometallic counterparts.     

Consequences of weak Allee effect on prey in the May–Holling–Tanner predator–prey model

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different ω ? limit sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Liquid–Liquid Phase Equilibrium and Ion-Exchange Exploration for Aqueous Two-Phase Systems of ([C4mim]Cl + K2CO3 or K3C6H5O7 + water) at Different Temperatures

Journal of Solution Chemistry - Liquid–liquid equilibrium (LLE) data and phase diagrams for new aqueous two-phase systems (ATPSs) containing 1-butyl-3-methylimidazolium chloride...     

Redox-Switchable Complexes Based on Nanographene-NHCs

A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced.     

Antiprotozoal and Antibacterial Activity of Ravenelin,a Xanthone Isolated from the Endophytic Fungus Exserohilum rostratum

The natural compound ravenelin was isolated from the biomass extracts of Exserohilum rostratum fungus, and its antimicrobial, antiplasmodial, and trypanocidal activities were evaluated. Ravenelin was isolated by column chromatography and HPLC and identified by NMR and MS. The susceptibility of Gram-positive and Gram-negative bacteria strains to ravenelin was determined by microbroth dilution assay. Cytotoxicity was evaluated in hepatocarcinoma cells (HepG2) and BALB/c peritoneal macrophages by using MTT. SYBR Green I-based assay was used in the asexual stages of Plasmodium falciparum. Trypanocidal activity was tested against the epimastigote and intracellular amastigote forms of Trypanosoma cruzi. Ravenelin was active against Gram-positive bacteria strains, with emphasis on Bacillus subtilis (MIC value of 7.5 µM). Ravenelin’s antiparasitic activities were assessed against both the epimastigote (IC₅₀ value of 5 ± 1 µM) and the intracellular amastigote forms of T. cruzi (IC₅₀ value of 9 ± 2 µM), as well as against P. falciparum (IC₅₀ value of 3.4 ± 0.4 µM). Ravenelin showed low cytotoxic effects on both HepG2 (CC₅₀ > 50 µM) and peritoneal macrophage (CC₅₀ = 185 ± 1 µM) cells with attractive selectivity for the parasites (SI values > 15). These findings indicate that ravenelin is a natural compound with both antibacterial and antiparasitic activities, and considerable selectivity indexes. Therefore, ravenelin is an attractive candidate for hit-to-lead development.