Gilles A. Lajoie

Dispersion copolymerization of styrene and divinylbenzene. II. Effect of crosslinker on particle morphology

The amount of divinylbenzene (DVB) that can be incorporated in a one-shot dispersion copolymerization with styrene to form a coagulum-free latex is low (<0.5%), a consequence of steric stabilizer immobilization and the inability of the system to provide sufficient quantities of new stabilization materials. Inclusion of a polystyrene solvent in the charge and/or addition of excess stabilizer shortly after the nucleation period enables 0.7% to be inserted, and up to 1% DVB can be copolymerized successfully by linear addition over the major particle growth period. Immobilization of some adsorbed stabilizer chains results in deviations from sphericity. Microparticles ranging from classic smooth-surfaced spheres at low DVB concentrations to node covered cups and heavily dented spheres at higher levels, can be synthesized. Furthermore, batch addition of 1-6% DVB at least 7 h after nucleation produces monodisperse, stable latexes comprising particles bearing deformities due, not to graft immobilization, but to phase separation within the crosslinked particle skin that forms after DVB absorption. Lower amounts of divinyl monomer batch added before the 7-h mark permits synthesis of a variety of spheroidal and pod-shaped microparticles.

Use of Marfey's reagent to quantitate racemization upon anchoring of amino acids to solid supports for peptide synthesis☆

A chromatographic assay has been developed to quantitate racemization occurring during attachment of protected amino acids to peptide synthesis resins. Acidolytic cleavage of deprotected amino acids from supports and subsequent derivatization with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfeys reagent) gave diastereomers separable by reverse-phase HPLC using aqueous acetonitrile. The assay is reliable to 0.1% racemate with a detection limit of approximately 100 pmol. The technique was applied to several acid-labile resins and was used to evaluate the racemizing characteristics of various anchoring methods.

Photo-control of nitric oxide synthase activity using a caged isoform specific inhibitor.

Nitric oxide (NO) plays a critical role in a number of physiological processes and is produced in mammalian cells by nitric oxide synthase (NOS) isozymes. Because of the diverse functions of NO, pharmaceutical interventions which seek to abrogate adverse effects of excess NOS activity must not interfere with the normal regulation of NO levels in the body. A method has been developed for the control of NOS enzyme activity using the localized photochemical release of a caged isoform-specific NOS inhibitor. The caged form of an iNOS inhibitor has been synthesized and tested for photosensitivity and potency. UV and multiphoton uncaging were verified using a hemoglobin-based assay. IC(50) values were determined for the inhibitor (70+/-11 nM), the caged inhibitor (1098+/-172 nM), the UV uncaged inhibitor (67+/-26 nM) and the multiphoton uncaged inhibitor (73+/-11 nM). UV irradiation of the caged inhibitor resulted in a 86% reduction in iNOS activity after 5 min. Multiphoton uncaging had an apparent first order time constant of 0.007+/-0.001 min(-1). A therapeutic range exists, with molar excess of inhibitor to enzyme from 3- to 7-fold, over which the full dynamic range of the inhibition can be exploited.

Evaluation of the metal binding properties of the histidine-rich antimicrobial peptides histatin 3 and 5 by electrospray ionization mass spectrometry.

Electrospray ionization mass spectrometry (ESI-MS) was used to investigate metal ion interactions with salivary peptides histatin 3 (H3) and histatin 5 (H5). Conformational changes of these peptides in the presence of metal ions were studied using circular dichroism spectroscopy. H3 and H5 formed high affinity complexes with Cu(2+) and Ni(2+) and, to a lesser extent, with Zn(2+). Both peptides show the potential for multiple binding sites for Cu(2+) and Ni(2+) and only a single strong binding site for Zn(2+). The binding of a third Cu(2+) ion to H3 seems to enable the binding of a fourth ion to H3. The binding of a second and third Ni(2+) ion to H5 has a similar effect in enabling the binding of a fourth ion. None of the metal ions examined stabilized a regular secondary structure for either peptide. Subtle changes in overall conformation are seen with the addition of Cu(2+) to both H3 and H5.

Characterisation of low molecular weight polymers using matrix assisted laser desorption time-of-flight mass spectrometry

Abstract Matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is used to mass characterise several low molecular weight, commercially available PS, PMMA and PEG samples. In addition, the utility of the technique for the study of polymer synthesis is demonstrated; different initiation and termination mechanisms leave dead chains with characteristic end groups which, in many cases, can be rapidly identified mass spectrometrically. There is broad agreement between MWDs derived from MALDI spectra and those obtained from conventional GPC analysis, but in some instances the differences are significant. Polydispersities obtained mass spectrometrically are invariably lower than those determined by GPC.

Chlorotrimethylsilane Mediated Formation of ω-Allyl Esters of Aspartic And Glutamic Acids

Abstract The protection of the ω-carboxylic function of aspartic and glutamic acids by an allyl ester is advantageous because of its orthogonality with most protecting groups and its compatibility with a number of reagents. In this communication we describe a simple method using chlorotrimethylsilane in the presence of allyl alcohol which gives exclusively the ω-allyl esters of both aspartic and glutamic acids in excellent yield.

Synthesis of N-protected N-methyl serine and threonine

Abstract Two efficient and convenient syntheses of N -Cbz and N -Fmoc N -methyl serine and threonine are described. The amino acid side-chain alcohol can be protected as a TBDMS ether in very good yield or left free, followed by the formation and subsequent reduction of the corresponding oxazolidinone.

Synthesis of enantiomerically enriched β,γ-unsaturated-α-amino acids

A variety of enantiomerically enriched beta,gamma -unsaturated-alpha -amino acids are synthesized by olefination of a Cbz-protected serine aldehyde equivalent, readily prepared from serine. A cyclic ortho ester protecting group is employed to minimize racemization. The deprotected amino acids are obtained in good yield, ranging from 70-95% ee, with double-bond geometry determined by the type of Wittig reagent used. Isotopically labeled side chains are readily introduced by this procedure, and free gamma-C-13-vinylglycine was prepared in 44% yield from the protected serine aldehyde synthon

A chemoenzymic synthesis of 1,5-dideoxy-1,5-imino-l-mannitol and l-rhamnitol and investigation of their effects on glycosidases

Abstract 1,5-Dideoxy-1,5-imino- l -rhamnitol ( 3 ) and 1,5-dideoxy-1,5-imino- l -mannitol ( 2 ), designed as inhibitors of α- l -rhamnosidase, have been synthesised from dihydroxyacetone phosphate and 3-azido-2-hydroxypropanal with the acid of partially purified E. coli l -rhamnulose 1-phosphate aldolase free of d -fructose 1,6-bisphosphate aldolase activity. Inhibitory effects of compounds 2 , 3 , 1,5-dideoxy-1,5-imino- d -mannitol, and 1,5-dideoxy-1,5-imino- d -glucitol ( 12 ) were tested on selected glycosidases. It has been found that compound 3 is a good inhibitor of α- l -rhamnosidase as well as α- l -fucosidases from bovine kidney and epididymis, 2 is a potent inhibitor of α-galactosidase and a moderate inhibitor of α- l -rhamnosidase, and 12 is a good inhibitor of α-galactosidase and α- l -rhamnosidase.

Stereoselective synthesis of allo-threonine and β-2H-allo-threonine from threonine

Abstract Both D- and L-allo-threonine can be synthesized in good yield from D- and L-threonine respectively, by protection of the amine with Fmoc and the carboxyl with a cyclic ortho ester, followed by oxidation of the side chain to a ketone, and diastereoselective reduction to the allo isomer. Deprotection gives the amino acid in 40% overall yield. The β-hydrogen can be labelled during reduction.