Synthesis, characterization, and evaluation of PS-PPDC resin: a novel flexible cross-linked polymeric support for solid-phase organic synthesis

The present study describes the synthesis of different mole densities of poly(propylene glycol)dimethacrylate cross-linked resins using monomer units such as styrene and 4-chloromethyl styrene and its evaluation as an ideal support toward different stages of solid-phase peptide synthesis. Free radical generated aqueous suspension polymerization has been followed for polymerization and the formation of resin was characterized using infrared and carbon-13 spectroscopic techniques. Surface morphology of resin was examined by scanning electron microscopy. The polymerization reaction was investigated with respect to the effect of amount of cross-linking agent to verify the swelling, loading, and the mechanical stability of resin. Solvent imbibition abilities in commonly used solvents were measured and compared to commercially available Merrifield as well as reported styrene-acryloyloxyhydroxypropyl methacrylate-tripropyleneglycol diacrylate (SAT resins. The chemical inertness of the support was also checked with different reagents used for solid-phase peptide synthesis. The suitability of support was demonstrated by synthesizing biologically potent Endothelin class of linear peptides by Fmoc strategy and compared to SAT resin. The purities of synthetic peptides were analyzed by high-performance liquid chromatography and corresponding masses by matrix-assisted laser desorption/ionisation-time of flight analysis.     

Synthesis of a shark repellent peptide toxin, Pardaxin (16-33) on a highly flexible polymer support: CLPSER

A high swelling resin, CLPSER has been developed and utilized for the solid phase synthesis of Pardaxin, which is an 18-residue peptide. The resin was characterized by gel phase (13)C NMR, IR and SEM. The utility of the new polymer support in polypeptide synthesis was further established by the comparative synthesis of pardaxin with commercially available Merrifield resin. The MALDI TOF MS, amino acid analysis and the HPLC revealed the superior quality of CLPSER.     

Tri(propylene glycol) glycerolate diacrylate cross-linked polystyrene: a new resin support for solid-phase peptide synthesis.

A highly flexible, mechanically and chemically stable copolymer, tri(propylene glycol) glycerolate diacrylate cross-linked polystyrene (PS-TRPGGDA), was synthesized by the suspension polymerization and employed as a solid support for peptide synthesis. The beaded polymer support containing secondary hydroxyl functional groups in the cross-linker was used as the growth site for peptide synthesis. The procedure is unique and cost-effective in that it avoids the initial functionalization steps required for most of the styrene-based polymer supports. The resin was characterized by 13C-CP-MAS NMR spectroscopy and the morphologic features of the resin were investigated using scanning electron microscopy. Swelling studies conducted on the new support revealed that the PS-TRPGGDA resin undergoes more effective swelling and solvation than PS-DVB resin in all solvents used in peptide synthesis. The efficiency of the new support was demonstrated by synthesizing a 'difficult' sequence Ala-Arg-(Ala)6-Lys and comparing it with commercially available Merrifield and Sheppard resins. The synthetic efficiency was further demonstrated by the synthesis of a 24-residue NR 2A peptide substrate of calcium/calmodulin-binding peptide. The high yield and purity of the peptide synthesized on the novel support indicates the positive role of the flexible and hydrophilic cross-linking agent in the solid support.     

Syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam)

The syntheses and characterization of novel binuclear chromium (III) complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) are described. The complex [(cyclam)Cr(OH)]₂Cl₄ · 7H₂O (1) crystallizes in the monoclinic space group C2/c with four binuclear formula units in a cell of dimensions a = 17.403 (2), b = 16.803 (3), c = 12.708 (2) Å, and β = 100.83 (1)°. The cation in 1 consists of di-μ-hydroxodichromium (III) units. The bridging OH groups lie on a twofold axis, which relates one end of the dimer to the other and gives rise to a rigorously planar Cr₂O₂ bridging unit. The Cr?Cr separation is 3.122 (1) Å and the average bridging Cr-O-Cr angle is 104.6 (4)°. The complex [(cyclam)Cr(SO₄)]₂ (ClO₄) · H₂O (5) crystallizes in the monoclinic space group P2₁/c with two binuclear formula units in a cell of dimensions a = 9.516 (2), b = 13.263 (3), c = 14.870 (3) Å, and β = 104.08 (3)°. This cation consists of bis-μ-sulfato-di-chromium (III) units, in which the two chromium centers are bridged by two bridging sulfate groups leading to an eight-membered {Cr-O-S-O}₂ bridging framework. Both dimers exhibit antiferromagnetic interactions, with J = 27.7 cm⁻¹ for complex 1 and J = 4.7 cm⁻¹ for complex 5. The EPR spectrum of the complex 1 has been simulated, demonstrating that the spectrum almost entirely originates from the quintet state, while a few lines can be attributed as triplet and septet transitions.     

Syntheses of oligomannosides in solution and on a soluble polymer support: a comparison

The alpha-(1-->6)-linked and the alpha-(1-->2)-linked linear mannotetraose glycosides and, respectively, and the branched mannopentaoside [R=CH2(CH2)2CH2Cl] were synthesised by conventional methods in solution, using trichloroacetimidate donors, and the products were obtained in 39%, 42% and 40% overall yield, respectively. For comparative purposes, the same two linear tetrasaccharides were prepared by use of MPEG as a soluble polymer support, the yields being 34% and 14%, respectively. An attempted MPEG-supported synthesis of the branched pentasaccharide was unsuccessful. The merits and shortcomings of oligosaccharide syntheses on MPEG are discussed.     

Crosslinked carboxymethylchitosan-g-poly(acrylic acid) copolymer as a novel superabsorbent polymer

A novel carboxymethylchitosan-g-poly(acrylic acid) (CMCTS-g-PAA) superabsorbent polymer was prepared through graft polymerization of acrylic acid onto the chain of carboxymethylchitosan and subsequent crosslinking. It was demonstrated by FTIR spectroscopy that acrylic acid had been graft polymerized with carboxymethylchitosan. The thermal stability of the polymer was characterized by thermogravimetric analysis. By studying the swelling ratio of the polymer synthesized under different conditions, optimization conditions were found for a polymer with the highest swelling ratio. The rate of water absorption of the polymer was high, and the swelling of the polymer fitted the process of first dynamics. The swelling ratio of the polymer was pH-dependent.     

Chiral chemical absorption property of a cross-linked poly(N-isopropyl acrylamide-co-sodium acrylate) thermoresponsive smart gel

This investigation leads to the chiral chemical absorption property of a thermoresponsive gel material. d ‐(+)‐α‐phenyl ethyl amine was taken as the chiral chemical. The gel material was synthesized by polymerizing 1:1 mole ratio of N‐isopropyl acrylamide and Na‐acrylate along with methylene bisacrylamide (2 wt.% of total monomer) as a cross‐linker using ammonium persulfate as an initiator and N, N, N′, N′‐tetra‐methyl ethylene diamine as an accelerator. The microporous nature of the gel material is observed by scanning electron microscope as well as by surface analysis. It is a pH as well as thermoresponsive gel. The highest gel swelling is observed at around pH 8.2 at room temperature (30 °C). The gel contains carboxylate (―COO^?) group in this slightly alkaline condition. In the ionic state, the mutual repulsion of the ionic groups helps in swelling the gel. The lower critical solution temperature (LCST) of the gel is observed to be about 38 °C, which is higher than that of poly N‐isopropyl acrylamide itself (32 °C). This corroborates with the theory and other reported results that LCST increases with the incorporation of ionic moiety in the cross‐linked copolymer. The chiral chemical absorption of the gel material was monitored by measuring circular dichroism of the chiral compound in the presence and absence of gel using a circular dichroism spectropolarimeter (J‐810 L) (JASCO International Co., Ltd., Tokyo, Japan). About 18% of d ‐(+)‐α‐phenyl ethyl amine is absorbed from its aqueous solution by 0.01 g of dry gel material (particle size: 106–212 µm) at room temperature. The absorption of the chiral compound is reversible with temperature having a sudden jump at LCST (38 °C) of the gel material. Chirality 24:506–511, 2012. © 2012 Wiley Periodicals, Inc.     

Hydrazide pharmaceuticals as conjugates to polyaldehyde dextran: syntheses, characterization, and stability.

The coupling of ellipticine and CI-921, two antineoplastic pharmaceuticals, to polyaldehyde dextran can be carried out under mild reaction conditions with novel acid hydrazides of the parent drugs. The resulting acyl hydrazones resist hydrolytic and enzymatic cleavage and offer a method for drug loading via dextran conjugates to monoclonal antibodies.     

Sonochemical syntheses and characterization of a new nano-structured one-dimensional lead(II) coordination polymer with 4,4,4-trifluoro-1-phenyl-1,3-butandione

A new nano-sized lead(II) one-dimensional coordination polymer with Pb?F interactions, [Pb(μ-TFPB)₂]_n (1) [TFPB⁻ = 4,4,4-trifluoro-1-phenyl-1,3-butandionate], has been synthesized and characterized by SEM, X-ray powder diffraction, IR spectroscopy and elemental analyses. The single-crystal X-ray data of compound 1 show that the Pb(II) atoms have a hemidirected coordination sphere with an environment of PbO₆F₂. The presence of a stereo-chemically active lone pair of the lead atom is apparently the reason that the neighboring bridging bond relative to gap of coordination sphere are so long. Therefore arrangement of “TFPB⁻” ligands suggests a gap or hole in coordination geometry around the lead(II) ions. PbO nanoparticles were obtained by calcination of the nano-sized compound 1 at 600 °C.     

Syntheses and pharmacological characterization of novel thiazole derivatives as potential mGluR5 PET ligands

Four novel thiazole containing ABP688 derivatives were synthesized and evaluated for their binding affinity towards the metabotropic glutamate receptor subtype 5 (mGluR5). (E)-3-((2-(Fluoromethyl)thiazol-4-yl)ethynyl)cyclohex-2-enone O-methyl oxime (FTECMO), the ligand with the highest binding affinity (K_i = 5.5 ± 1.1 nM), was labeled with fluorine-18. [¹⁸F]-FTECMO displayed optimal lipophilicity (log D_pH7.4 = 1.6 ± 0.2) and high stability in rat and human plasma as well as sufficient stability in rat liver microsomes. In vitro autoradiography with [¹⁸F]-FTECMO revealed a heterogeneous and displaceable binding in mGluR5-rich brain regions. PET imaging with [¹⁸F]-FTECMO in Wistar rats, however, showed low brain uptake. Uptake of radioactivity into the skull was observed suggesting in vivo defluorination. Thus, although [¹⁸F]-FTECMO is an excellent ligand for the detection of mGluR5 in vitro, its in vivo characteristics are not optimal for the imaging of mGluR5 in rats in vivo.     

Pancreatic spasmolytic polypeptide (PSP): I. Preparation and initial chemical characterization of a new polypeptide from porcine pancreas

A novel polypeptide, named Pancreatic Spasmolytic Polypeptide (PSP), was discovered in a side-fraction from the purification of porcine insulin. PSP was prepared by two different purification methods based on combinations of precipitations, anion-exchange and cation-exchange chromatography. The highest yield obtained, 52 mg PSP/kg pancreas, indicates that the content of PSP in porcine pancreas is about half the content of insulin. Both preparations appeared to be very pure as judged by basic disc electrophoresis, isoelectric focusing, analytical gel filtration and radioimmunoassays for various polypeptides known to be present in pancreas. The PSP molecule contains 106 amino acids (MW about 11 700). PSP is an acidic (pI 4.4), non-glycosylated protein without free N-terminal amino groups, and with high contents of proline and cystine. The high content of S-S bridges (7 per molecule), an unexpected low apparent MW determined by gel filtration, and a remarkable resistance towards treatment with trypsin and chymotrypsin, point to a compact structure of the PSP molecule.     

Immunolocalization of a novel, cytoskeleton-associated polypeptide of Mr 230,000 daltons (p230)

Antibodies were raised against a cytoskeleton-associated, nonphosphorylated, 230,000-dalton bovine lens polypeptide (designated p230), and rendered monospecific by using a novel immunoaffinity technique. In immunofluorescence and electron microscopy of cultured fibroblasts, as well as of various other cells (endothelial, epithelial, lenticular, monocytes, neuroblastoma cells) and tissues (human kidney and liver), p230 was localized as a distinct subplasmalemmal layer in the peripheral cytoplasm of the cells. It constituted less than 0.3% of the total cellular protein in cultured fibroblasts and was not extractable with Triton X-100. In detergent-extracted cytoskeletal preparations of cultured fibroblasts, p230 remained as an elaborate peripheral network that showed a distribution distinctly different from that of the major cytoskeletal structures, stress fibers, cortical myosin, vinculin, and intermediate filaments (IF). The distribution was not dependent on the presence of intact stress fibers or microtubules, as shown by double-fluorescence microscopy of cells exposed to cytochalasin B or cultured in the presence of monensin and of cold-treated cells. Upon demecolcine-induced reorganization of intermediate filaments, however, the localization of p230 was rapidly altered to a dense plaque underneath the perinuclear aggregate of intermediate filaments. On the other hand, p230 seemed to colocalize with the detergent-resistant cell surface lamina, visualized in fluorescence microscopy with fluorochrome-coupled wheat germ agglutinin-lectin. The results suggest that p230 is part of a cell surface- and cytoskeleton-associated subplasmalemmal structure that may play an important role in cell surface-cytoskeleton interaction in various cells both in vitro and in vivo.     

Synthesis of polypeptide models of elastin. Synthesis and properties of a cross-linked polytetrapeptide

Synthesis of two copolymers, H-(phi-Pro-Gly-Gly)n-Val-OMe and H-(phi'-Pro-Gly-Gly)n-Val-OMe, where phi is Val or Lys and phi' is Val or Glu is described. Cross-linking between the two copolymers is achieved by a coupling reaction between the epsilon-amino groups of the lysine containing copolymer and delta-carboxyls of the glutamic acid of the other copolymer. The cross-linking reaction was performed during a temperature elicited phase separation with flow orientation of the copolymers. Coacervation of the intermediate polymers is presented, as is the scanning electron micrograph of the insoluble cross-linked product and its calcifiability as determined with electron probe microanalysis. The purity of the key intermediates and polymers is demonstrated by the usual analytical methods. Carbon-13 magnetic resonance spectra of the intermediate monomer units are included to validate the purity of their synthesis.     

Isolation, identification and characterization of a novel triazophos-degrading Bacillus sp. (TAP-1)

A novel triazophos-degrading Bacillus sp., TAP-1, was isolated from sewage sludge in a wastewater treating system of organophosphorus pesticide produced by Funong Group Co. in Jianou, Fujian, southeastern China. The isolate is a gram-positive and rod-shaped bacterium capable of hydrolyzing insecticide triazophos and was identified as a strain of Bacillus using polyphasic taxonomy combined with analysis of the morphological and physio-biochemical properties. TAP-1 could degrade triazophos through co-metabolism. When fed with nutrients such as yeast extract, peptone and glucose, TAP-1 could degrade 98.5% of TAP in the medium (100 mg/l) within 5 days. The optimal pH and temperature for the degradation were 6.5-8 and 32°C, respectively. An enzyme distribution experiment showed that the enzyme responsible for TAP degradation appeared to be intracellular.     

Dual stimuli-responsive polypeptide prepared by thiol-ene click reaction of poly(l-cysteine) and N,N-dimethylaminoethyl acrylate

Stimuli-responsive polymers that can undergo conformational changes with external triggers have enabled themselves as smart materials for various utilizations, among which biodegradability is of particular importance to be engineered for biomedical application. In this study, a thermo and pH dual responsive polypeptide (N, N-dimethylaminoethyl acrylate-modified poly(l -cysteine)) (PLC-g-DMAEA) was prepared by the combination of N-carboxyanhydride ring-open polymerization and thiol-ene click chemistry. The biodegradable poly(l -cysteine) (PLC) with pendant thiol groups provided an easily clickable backbone for postmodification, which was demonstrated by reacting with a well-known monomer of N, N-dimethylaminoethyl acrylate (DMAEA) to achieve both temperature and pH responsiveness. The irreversible thermo-response of PLC-g-DMAEA could be attributed to the ordered β-sheets formed upon heating, leading to the trapped side groups with poor water accessibility. Moreover, this copolymer precipitated at pH ranging from 7.5 to 9.7, but protonation of tertiary amine groups (pH < 7.5) and salt forming of masked thiol groups (pH > 9.7) rendered it soluble in water. Our results revealed that a ready available vinyl monomer could be easily clicked onto the biodegradable PLC and its stimuli responsiveness would be reserved. Moreover, the primary and secondary structures of PLC might influence the conformation, thus leading to the unique responsive behavior of the resulted copolymer.     

Synthesis, swelling behavior, and biocompatibility of novel physically cross-linked polyurethane-block-poly(glycerol methacrylate) hydrogels

Physically cross-linked novel block copolymer hydrogels with tunable hydrophilic properties for biomedical applications were synthesized by controlled radical polymerization of polyurethane macroiniferter and (2,2-dimethyl-1,3-dioxolane) methyl methacrylate. The block copolymers were converted to hydrogels by the selective hydrolysis of poly[(2,2-dimethyl-1,3-dioxolane) methyl methacrylate] block to poly(glycerol methacrylate). The block copolymerization has been monitored by monomer conversion and molecular weight increase as a function of time. It was observed that the polymerization proceeded with a characteristic "living" behavior where both monomer conversion and molecular weight increased linearly, with increasing reaction time. The resulting hydrogels were investigated for their equilibrium water content (EWC), dynamic water contact angles, swelling kinetics, thermodynamic interaction parameters, plasma protein adsorption, and platelet adhesion. Similar to our previous mechanically responsive hydrogels (Mequanint, K.; Sheardown, H. J. Biomater. Sci. Polym. Ed. 2005, 10, 1303-1318), the present results indicated that block copolymer hydrogels have excellent hydrophilicity and swelling behavior with improved modulus of elasticity. The equilibrium swelling was affected by the hydrolysis time, block length of poly(glycerol methacrylate), temperature, and the presence of soluble salts. Fibrinogen adsorption and platelet adhesion were significantly lower for the hydrogels than for the control polyurethane, whereas albumin adsorption increased for the hydrogels in proportion to the contents of poly(glycerol methacrylate). These hydrogels have potential in a number of biomedical applications such as drug delivery and scaffolds for tissue engineering.     

Chymotrypsin adsorbed to a polyethylene terephtalate support (SORSILEN) as a suitable model for the investigation of enzymatically catalyzed organic syntheses in nonaqueous media

Summary The kinetics of acetyl-L-tryptophan esterification by ethanol in an organic solvent immiscible with water (chloroform) and catalyzed by chymotrypsin adsorbed from aqueous solution to a polyethylene terephthalate copolymer (SORSILEN) was examined by HPLC. The esterification yield (in %) increased with the decreasing concentration of the substrate and with the increasing activity of immobilized chymotrypsin. It has been shown that there was no chymotrypsin leakage from the aqueous phase on the support surface during the catalysis.