The dynamics of GATG glycodendrimers by NMR diffusion and quantitative (13)C relaxation

The dynamics of GATG glycodendrimers have been investigated by NMR translational diffusion and quantitative (13)C relaxation studies (Lipari-Szabo model-free), allowing the determination of the correlation times describing the dendrimer segmental orientational mobility.

Preparation and evaluation of alpha-phenyl-n-tert-butyl nitrone (PBN)-encapsulated chitosan and PEGylated chitosan nanoparticles

Alpha-phenyl-n-tert-butyl nitrone (PBN) shows its major effect by scavenging free radicals formed in the ischemia and it has the ability to penetrate through the blood brain barrier easily. The in vivo stability of PBN is very low and when administered systemically, it has a mean plasma half life of about three hours. Therefore, formulations which are able to prolong the plasma residence time of PBN are of major interest, because oxygen radicals are usually continuously formed under pathological conditions. In this study, PBN, a nitrone compound having neuroprotective properties, was encapsulated in chitosan (CS) and chitosan-poly(ethylene glycol) (CS-PEG) nanoparticles for treatment of diseases such as stroke, in which sustained free radical production is reported. The nanoparticles were characterized through particle size determination, zeta potential, encapsulation efficiency, surface morphology determinations and in vitro release studies. The surface morphologies were evaluated by transmission electron microscopy (TEM) and nanoparticles having spherical shapes were characterized. The particle size distribution was between approximately 97 nm and approximately 322 nm; and the zeta potentials varied between approximately 9 mV and approximately 33 mV. Size of the nanoparticle formulations was important for the release of PBN from nanoparticles. The quantitative determination of PBN has been evaluated by a validated analytical HPLC method. The presented chitosan-based nanotechnology opens new perspectives for testing antioxidant activity in vivo.

Surpassing the use of copper in the click functionalization of polymeric nanostructures: a strain-promoted approach

The limitations (depolymerization and Cu contamination) in the use of Cu(I)-catalyzed azide-alkyne [3 + 2] cycloadditions (CuAAC) for the selective click functionalization of polysaccharide-based systems have been efficiently surpassed using a strain-promoted approach (SPAAC). The SPAAC decoration of chitosan-g-poly(ethylene glycol) nanostructures with an immunoglobulin G under physiological conditions represents a step forward in the preparation of immunonanoparticles.

DTD, an anti-inflammatory ditriazine, inhibits angiogenesis in vitro and in vivo

The ditriazine derivative DTD (4,10-dichloropyrido[5,6:4,5]thieno[3,2-d':3,2-d]-1,2,3-ditriazine) has been previously reported to reduce the degree of granulomatous inflammation and vascular density in a murine air pouch granuloma model. The aim of this study was to test whether DTD affects angiogenesis. Our results show that DTD inhibits in vivo angiogenesis in the chorioallantoic membrane (CAM) assay at doses equal or lower than 0.3 nmol/egg. Different in vitro assays were used to study the potential effects of this compound on key steps of angiogenesis, namely, a colorimetric assay of cell proliferation/viability, a morphogenesis on Matrigel assay, zymographic assays for gelatinases and nuclear morphology and cell cycle analysis for apoptosis induction. Our data indicate that DTD inhibits proliferation but does not induce apoptosis in endothelial cells in vitro. DTD suppresses the endothelial capillary-like chord formation at concentrations lower than those required to inhibit proliferation. DTD treatment inhibits the matrix metalloproteinase-2 production in endothelial and fibrosarcoma cells, but does not affect the cyclooxygenase-2 expression in endothelial cells, as assessed by western blot analysis. Taken together, results here presented indicate that DTD exhibits an anti-angiogenic activity that is independent of inflammatory processes and make it a promising drug for further evaluation in the treatment of angiogenesis-related pathologies.

In tube determination of the absolute configuration of alpha- and beta-hydroxy acids by NMR via chiral BINOL borates

A simple NMR methodology, through the formation of chiral BINOL borates in the NMR tube, and that reunites the advantages of chiral derivatizing (CDAs) and chiral solvating agents (CSAs), is presented for the assignment of the absolute configuration of alpha- and beta-hydroxy acids.

Paramagnetic NMR relaxation in polymeric matrixes: sensitivity enhancement and selective suppression of embedded species (1H and 13C PSR filter)

A study of the practical applications of the addition of paramagnetic spin relaxation (PSR) ions to a variety of polymers (PLL, PAA, PGA, PVP, and polysaccharides such as hyaluronic acid, chitosan, mannan, and dextran) in solution (D2O and DMSO-d6) is described. Use of Gd(III), Cu(II), and Mn(II) allows a reduction of up to 500% in the 1H longitudinal relaxation times (T1), and so in the time necessary for recording quantitative NMR spectra (sensitivity enhancement) neither an increase of the spectral line width nor chemical shift changes resulted from addition of any of the PSR agents tested. Selective suppression of the 1H and 13C NMR signals of certain components (low MW molecules and polymers) in the spectrum of a mixture was attained thanks to their different sensitivity [transverse relaxation times (T2)] to Gd(III) (PSR filter). Illustration of this strategy with block copolymers (PGA-g-PEG) and mixtures of polymers and low MW molecules (i.e., lactose-hyaluronic acid, dextran-PAA, PVP-glutamic acid) in 1D and 2D NMR experiments (COSY and HMQC) is presented. In those mixtures where PSR and CPMG filters alone failed in the suppression of certain components (i.e., PVP-mannan-hyaluronic acid) due to their similarity of 1H T2 values and sensitivities to Gd(III), use of the PSR filter in combination with CPMG sequences (PSR-CPMG filter) successfully resulted in the sequential suppression of the components (hyaluronic acid first and then mannan).

Antitumor Activity, X-ray Crystal Structure, and DNA Binding Properties of Thiocoraline A, a Natural Bisintercalating Thiodepsipeptide

The marine natural product thiocoraline A displayed approximately equal cytotoxic activity at nanomolar concentrations in a panel of 12 human cancer cell lines. X-ray diffraction analyses of orthorhombic crystals of this DNA-binding drug revealed arrays of docked pairs of staple-shaped molecules in which one pendent hydroxyquinoline chromophore from each cysteine-rich molecule appears intercalated between the two chromophores of a facing molecule. This arrangement is in contrast to the proposed mode of binding to DNA that shows the two drug chromophores clamping two stacked base pairs, in agreement with the nearest-neighbor exclusion principle. Proof of DNA sequence recognition was obtained from both classical DNase I footprinting experiments and determination of the melting temperatures of several custom-designed fluorescently labeled oligonucleotides. A rationale for the DNA-binding behavior was gained when models of thiocoraline clamping a central step embedded in several octanucleotides were built and studied by means of unrestrained molecular dynamics simulations in aqueous solution.

Relative and Absolute Stereochemistry of Secondary/Secondary Diols: Low-Temperature 1H NMR of Their bis-MPA Esters

Comparison of the room- and low-temperature 1H NMR spectra of the bis-(R)- or bis-(S)-MPA ester derivative of an open chain sec,sec-1,2-diol allows the easy determination of its relative stereochemistry and in some cases absolute configuration. If the diol is anti, its absolute configuration can be directly deduced from the signs of DeltadeltaT1T2 for substituents R1/R2, but if the relative stereochemistry of the diol is syn, the assignment of its absolute configuration requires the preparation of two derivatives (both the bis-(R)- and bis-(S)-MPA esters), comparison of their room-temperature 1H NMR spectra, and calculation of the DeltadeltaRS signs for the methines Halpha(R1) and Halpha(R2) and R1/R2 protons. The reliability of these correlations is validated with 17 diols of known absolute configuration used as model compounds.

Conjugation of Bioactive Ligands to PEG-Grafted Chitosan at the Distal End of PEG

Graft copolymers of chitosan and PEG-CO(2)H incorporating biologically active molecules and tags (mannose, cholesterol, a coumarin dye, and biotin) at the distal end of poly(ethylene glycol) (PEG) have been synthesized in excellent yields and nearly quantitative mass recoveries. Experimental conditions allowing the preparation of multifunctional graft copolymers incorporating simultaneously several of those active molecules and tags in controlled ratios are also presented. The required functionalized PEG-CO(2)H conjugates have been prepared from a heterodifunctional PEG and the experimental conditions established to ensure the purity of PEG end groups ((1)H and (13)C NMR and matrix-assisted laser desorption/ionization mass spectrometry-time of flight (MALDI-TOF)) and the completion of each synthetic step.

Challenging the absence of observable hydrogens in the assignment of absolute configurations by NMR: application to chiral primary alcohols

The absolute configuration of beta-chiral primary alcohols devoid of observable hydrogens on one of the beta-substituents at the asymmetric carbon (L(1)/L(2)) can be determined by comparison of the (1)H NMR of their (R)- and (S)-9-AMA ester derivatives and analysis of the Deltadelta(RS) for the L substituent and the Cbeta-H.

“Clickable” PEG−Dendritic Block Copolymers

Three generations of azido-terminated PEG-dendritic block copolymers have been synthesized and completely characterized by NMR and MALDI-TOF. A radial decrease of density, leading to more mobile protons at the outermost periphery, and an increasingly higher compactness of the core with generation have been determined by T(1) and T(2) relaxation time studies. The efficient surface decoration of these dendritic polymers by means of click chemistry has been demonstrated by the incorporation of unprotected carbohydrate units in very good to excellent yields. The reaction proceeds at room temperature, under aqueous conditions, and requires just catalytic amounts of Cu. The modified block copolymers are conveniently purified by ultrafiltration. The glycodendrimers functionalized with alpha-mannose form aggregates with concanavalin A as determined by absorbance experiments at 400 nm. This aggregation ability increases with generation.