Chemoselective O-methylation of N-acylated/sulfonylated tyrosine derivatives

Methyl ethers (6a and 6b) of N-trifluoroacetyl- and N-(m-trifluoromethyl) phenylsulfonyl-6-nitro-tyrosine t-butyl ester were readily prepared by modified Mitsunobu reaction (DPPE. DIAD, MeOH). Williamson (Mel, K2CO3 or LiCO3 or NaOH under phase transfer) and classical Mitsunobu conditions (PPh3, DEAD, MeOH) gave O,N-dimethylated derivatives (7a and 7b) as side or main products. O- versus N-selectivity in tyrosine methylation reactions depends on both pK(a) values and steric factors. (C) 2002 Elsevier Science Ltd. All rights reserved

Effect of the chemical nature and length of spacer arms on the covalent grafting of fluorinated molecular probes at the surface of poly(ethylene terephthalate) membrane

A series of fluorinated molecular probes were synthesized that are characterized by spacer arms of various lengths and polarities. Previous molecules (1, 2a, 2b, 2c, 3a, 3b) were covalently fixed on the surface of poly(ethlylene terephthalate) (PET) membranes via activated hydroxyl chain endings. X-ray photoelectron microscopic analysis of the grafted samples allowed us to quantify the PET surface reactivity; the results were within 40-50 pmol/cm(2) of fixed probes, independent of the length and hydrophilicity of the spacer arms. (C) 2002 Wiley Periodicals, Inc

Radiolabeling of Pluronic amphiphilic copolymer for adsorption studies.

A new pathway for the radiolabeling of Pluronic PE6800 was developed. In a first step, the CH(2)-OH end groups of the copolymer were substituted by tosylates; in a second step these were reduced by [3H]-NaBH(4) to obtain tritiated chain ends. The final product was shown to be a mixture of native, tosylated, and reduced Pluronic containing 1 tritium atom per 1110 Pluronic molecules. The labeling procedure did not affect the molecular weight distribution nor the adsorption isotherm of the copolymer on polystyrene plates. A plateau value of about 0.7 microg/cm(2) is reached at a concentration in solution of 500 microg/ml, i.e., much lower than the cmc. Upon drying, the Pluronic adsorbed layer reorganizes in particles with a size of about 30 to 60 nm which cover about 15% of the substratum surface. This observation is of great importance for the design of protein-resistant surfaces by adsorption of Pluronic

Novel RGD-like molecules based on the tyrosine template design, synthesis, and biological evaluation on isolated integrins alpha(V)beta/alpha(IIb)beta(3) and in cellular adhesion tests

RGD (Arg-Gly-Asp) peptidomimetics have been designed for covalent anchorage on biomaterials. The tyrosine template was thus equipped with (i) a basic side chain of various flexibility, (ii) an acidic side chain, which incorporated the XPS fluorine tag, and (iii) a spacer-arm terminated by a primary amine for surface grafting. The most active compounds showed IC50 values in the nanomolar range versus isolated human integrins alpha(v)beta(3) and alpha(IIb)beta(3). Preincubation of CaCo2 cells with soluble peptidomimetics (2 and 19a) prevented cellular adhesion on culture plates coated with vitronectin. On the other hand, peptidomimetics (19a and 19b) immobilized on a poly(ethylene)terephthalate membrane (PET) promoted CaCo2 cells adhesion. A modeling study at the ab initio level in MINI-1' basis allowed to compare the various synthetic ligands of integrins and to propose novel pharmacophore structures. (C) 2004 Elsevier Ltd. All rights reserved

Submicrometer-scale heterogeneous surfaces by PS-PMMA demixing

Patterned surfaces were created using two polymers: polystyrene (PS) on the one hand, and either poly(methyl methacrylate) (PMMA) or poly(methyl methacrylate)-poly(methacrylic acid) (PMMA-PMAA) on the other hand. PMMA was dissolved in a solvent of PS; this solution was then spin-coated on a PS support that partially dissolved during the process. The materials were analyzed by water contact angle measurement, XPS, ToF-SIMS and AFM. The effect of the solvent on the final surface morphology was strongly marked. With chloroform, the acrylic polymer was the major surface constituent, possibly because of the high evaporation rate of this solvent. With toluene, which is a better solvent for PS compared to PMMA, the obtained surface was almost exclusively constituted of PS. The use of chlorobenzene provided inclusions of acrylic polymer in PS, both polymers being exposed at the outermost surface. The surface morphology presented rings, the interior of which consisted of the acrylic polymer, while the rest of the surface was made of PS. (C) 2004 Elsevier Ltd. All rights reserved

aVb3 integrin-targeting Arg-Gly-Asp (RGD) peptidomimetics containing oligo ethylene glycol (OEG) spacers

RGD peptides are used in biomaterials science for surface modifications with a view to elicit selective cellular responses. Our objective is to replace peptides by small peptidomimetics acting similarly. We designed novel molecules targeting alpha(v)beta(3) integrin and featuring spacer-arms (for surface grafting), which do not disturb the biological activity, from (l) N-(3-(trifluoromethyl)benzenesulfonyl) tyrosine used as scaffold. Various Arg-mimics were fixed on the phenol function, and the ortho position was used for the coupling of OEG spacers. All peptidomimetics were active in the nM range in a binding test toward human alpha(v)beta(3) integrin (IC(50) = 0.1 to 1.7 nM) and selective versus platelet integrin alpha(IIb)beta(3). Selected compounds revealed excellent ability to inhibit bone cells adhesion on vitronectin. Modeling and docking studies were performed for comparing the most active RGD peptidomimetic to cilengitide, i.e., cyclo-[RGDfN(Me)V]-. Lastly, the adhesion of endothelial cells on a cultivation support grafted with RGD peptidomimetics was significantly improved