Organometallic gold(III) compounds as catalysts for the addition of water and methanol to terminal alkynes

Different inorganic and organometallic gold(III) and gold(I) complexes have been tested in the addition of water and methanol to terminal alkynes. Anionic and neutral organometallic gold(III) compounds can efficiently mediate these reactions in neutral media in refluxing methanol. The compounds are added in catalytic amounts (1.6-4.5 mol % with respect to the alkyne). Thus, compounds of the general formula Q[AuRCl(3)], Q[AuR(2)Cl(2)], [AuRCl(2)](2), and [AuR(2)Cl](2) (Q = BzPPh(3)(+), PPN: N(PPh(3))(2)(+) or N(Bu)(4)(+); R = C(6)F(5) or 2,4,6-(CH(3))(3)C(6)H(2)) seem to behave as Lewis acids in nucleophilic additions to triple bonds. Some intermediates could be detected in the stoichiometric reaction between [Au(C(6)F(5))(2)Cl](2) and phenylacetylene that was followed by variable temperature (1)H, (19)F[(1)H], COSY (19)F[(1)H]-(19)F[(1)H], and (2)H[(1)H] NMR experiments. Compound [Au(C(6)F(5))(2)Cl](2) is also able to catalyze the hydration of phenylacetylene at room temperature. A plausible mechanism for the hydration reaction has been proposed.     

Two Interrelated Strategies for Cephalotaxine Synthesis

Studies of two interrelated strategies for the synthesis of members of the cephalotaxus alkaloid family have culminated in a concise route for the preparation of the parent member cephalotaxine (1). As part of efforts exploring the use of an SET-promoted photocyclization reaction of aryl-substituted silylallyliminium salts to generate the spirocyclic DE unit of the target, we noted that attempts to generate the pentacyclic amino ketone 23 by deacylation of the enol ester 20 led to production of a mixture of 23 and the macrocyclic amino enone 24. A rapid equilibrium was shown to exist between 23 and 24, favoring the latter ring-opened form. This contrasts with the behavior of desmethylcephalotaxinone (22), a key late intermediate in several earlier cephalotaxine syntheses, which is known to exist in a ring-closed form. These observations led to the design of a second generation strategy which relies on transannular cyclization of the macrocyclic amino enedione 28. In practice, the sequence following this design transforms the known iodopiperonylethanol derivative 4 to 22 in 13 steps and a 12% overall yield and, thus, corresponds to an efficient formal synthesis of cepahalotaxine.     

Human symbiont Bacteroides thetaiotaomicron synthesizes 2-keto-3-deoxy-D-glycero-D- galacto-nononic acid (KDN)

The proper functioning of the human intestine is dependent on its bacterial symbionts, the most predominant of which belong to the Phylum Bacteroidetes. These bacteria are known to use variable displays of multiple capsular polysaccharides (CPs) to aid in their survival and foraging within the intestine. Bacteroides thetaiotaomicron is a prominent human gut symbiont and a remarkably versatile glycophile. The structure determination of the CPs, encoded by the eight CP loci, is the key to understanding the mechanism of this organism's adaptation on a molecular level. Herein, we report the bioinformatics-based discovery and chemical demonstration of a biosynthetic pathway that forms and cytidylates 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN), most likely for inclusion in the CP encoded by B. thetaiotaomicron CP locus 7.     

Unusual behavior of the aqueous solutions of gemini bispyridinium surfactants: apparent and partial molar enthalpies of the dimethanesulfonates

Apparent and partial molar enthalpies at 298 K of the aqueous solutions of cationic gemini surfactants 1,1'-didodecyl-2,2'-dimethylenebispyridinium dimethanesulfonate (12-Py(2)-2-(2)Py-12 MS); 1,1'-didodecyl-2,2'-trimethylenebispyridinium dimethanesulfonate (12-Py(2)-3-(2)Py-12 MS); 1,1'-didodecyl-2,2'-tetramethylenebispyridinium dimethanesulfonate (12-Py(2)-4-(2)Py-12 MS); 1,1'-didodecyl-2,2'-octamethylenebispyridinium dimethanesulfonate (12-Py(2)-8-(2)Py-12 MS); 1,1'-didodecyl-2,2'-dodecamethylenebispyridinium dimethanesulfonate (12-Py(2)-12-(2)Py-12 MS) were measured as a function of concentration and are here reported for the first time. They show a very peculiar behavior as a function of the spacer length, not allowing for the determination of a -CH 2- group contribution when this group is added to the spacer. The curve of the compound with a four-carbon-atom-long spacer lies between those of the compound with a spacer of 2 and 3 carbon atoms, instead of that below the latter, as expected. This surprising behavior, never found before in the literature and different from that found for the more popular m- s- m-type bisquaternary ammonium gemini surfactants, could be explained by a conformation change of the molecule, caused by stacking interactions between the two pyridinium rings, mediated by the counterion and appearing at an optimum length of the spacer. The hypothesis is also supported by the data obtained from the surface tension vs log c curves, showing that A min, the minimum area taken at the air-water interface by the molecule, is significantly lower for 12-Py(2)-4-(2)Py-12 MS than that of the other compounds of the same homologous series, and that the same compound has a greater tendency to form micelles instead of adsorbing at the air/water interface. The evaluation of the micellization enthalpies, by means of a pseudophase transition model, agrees with the exposed trends. These results confirm the great crop of information that can be derived from the study of the solution thermodynamics of aggregate systems and in particular from the curves of apparent and molar enthalpies vs concentration.     

in vitro biological evaluation of folate-functionalized block copolymer micelles for selective anti-cancer drug delivery

The main objective of this study was to evaluate the ability of folic acid-functionalized diblock copolymer micelles to improve the delivery and uptake of two poorly water-soluble anti-tumor drugs, tamoxifen and paclitaxel, to cancer cells through folate receptor targeting. The diblock copolymer used in this study comprised a hydrophilic poly[2-(methacryloyloxy)ethyl phosphorylcholine] (MPC) block, carrying at the chain end the folate targeting moiety, and a pH-sensitive hydrophobic poly[2-(diisopropylamino)ethyl methacrylate] (DPA) block (FA-MPC-DPA). The drug-loading capacities of tamoxifen- and paclitaxel-loaded micelles were determined by high performance liquid chromatography and the micelle dimensions were determined by dynamic light scattering and transmission electron microscopy. Cell viability studies were carried out on human chronic myelogenous leukaemia (K-562) and colon carcinoma cell lines (Caco-2) in order to demonstrate that drug-loaded FA-MPC-DPA micelles exhibited higher cytotoxicities toward cancer cells than unfunctionalized MPC-DPA micelles. Uptake studies confirmed that folate-conjugated micelles led to increased drug uptake within cancer cells, demonstrating the expected selectivity toward these tumor cells.     

Hydrogels for potential colon drug release by thiol-ene conjugate addition of a new inulin derivative

Inulin was chosen as a starting polymer for biocompatible, pH-sensitive and biodegradable hydrogels. Three INUDVSA-TT hydrogels were obtained by crosslinking inulin derivatives with trimethylolpropane tris(3-mercaptopropionate) under varying conditions. The resulting hydrogels were cell compatible, as demonstrated by MTS and trypan blue exclusion assays acting on Caco-2 cells, and were biodegraded by inulinase and esterase, thus suggesting their use as colonic drug delivery systems. 2-Methoxyestradiol, an anti-cancer drug, was soaked in INUDVSA-TT hydrogels and its in vitro release and apoptotic effect on Caco-2 cells were evaluated.     

A nanoparticulate drug-delivery system for rivastigmine: physico-chemical and in vitro biological characterization

The preparation and characterization of surface-PEGylated polymeric nanoparticles are described. These systems were obtained by UV irradiation of PHM and PHM-PEG(2000) as an inverse microemulsion, using an aqueous solution of the PHM/PHM-PEG(2000) copolymer mixture as the internal phase and triacetin saturated with water as the external phase, and characterized by dimensional analysis, zeta-potential measurements and XPS. in vitro biological tests demonstrated their cell compatibility and their ability to escape from phagocytosis. Rivastigmine was encapsulated into the nanoparticle structure and drug-release profiles from loaded samples were investigated in PBS at pH = 7.4 and human plasma.     

Surface Tension of Liquid Organic Acids: An Artificial Neural Network Model

An artificial neural network model is proposed for the surface tension of liquid organic fatty acids covering a wide temperature range. A set of 2051 data collected for 98 acids (including carboxylic, aliphatic, and polyfunctional) was considered for the training, testing, and prediction of the resulting network model. Different architectures were explored, with the final choice giving the best results, in which the input layer has the reduced temperature (temperature divided by the critical point temperature), boiling temperature, and acentric factor as an independent variable, a 41-neuron hidden layer, and an output layer consisting of one neuron. The overall absolute percentage deviation is 1.33%, and the maximum percentage deviation is 14.53%. These results constitute a major improvement over the accuracy obtained using corresponding-states correlations from the literature.     

Design,Synthesis and Characterization of a Visible-Light-Sensitive Molecular Switch and Its PEGylation Towards a Self-Assembling Molecule

HBDI-like chromophores represent a novel set of biomimetic switches mimicking the fluorophore of the green fluorescent protein that are currently studied with the hope to expand the molecular switch/motor toolbox. However, until now members capable of absorbing visible light in their neutral (i. e. non-anionic) form have not been reported. In this contribution we report the preparation of an HBDI-like chromophore based on a 3-phenylbenzofulvene scaffold capable of absorbing blue light and photoisomerizing on the picosecond timescale. More specifically, we show that double-bond photoisomerization occurs in both the E-to-Z and Z-to-E directions and that these can be controlled by irradiating with blue and UV light, respectively. Finally, as a preliminary applicative result, we report the incorporation of the chromophore in an amphiphilic molecule and demonstrate the formation of a visible-light-sensitive nanoaggregated state in water.