N-(o-carboxybenzyl) chitosans: Novel chelating polyampholytes

The imine formed by chitosan with phthalaldehydic acid was reduced with sodium cyanoborohydride and the resulting N-(o-carboxybenzyl) chitosan (NCBC) was insolubilised with ethanol and acetone and obtained as a white, free-flowing powder, soluble in both acidic and alkaline solutions. A sample of NCBC with the following degrees of substitution: acetamido 42%±4%, N-(o-carboxybenzyl) amine 43%±3%, free amine 15%±1% and containing 16%±1% moisture, was characterised by IR and UV-Vis. spectrometry, titration and viscometry. The isoelectric point was 6·8; the pK_a values were 5·7 and 8·0. NCBC could be determined by UV-Vis. spectrophotometry in aqueous solutions at 274 nm; maximum viscosity of the solutions was observed at pH 4. Upon addition of NCBC to transition metal ion solutions (0·1–0·5 mm) chelation and insolubilisation took place immediately. The dependence of the collection percentage on pH, NCBC and metal ion concentrations was studied for nine metal ions.     

Sulfated N-(carboxymethyl)chitosans: Novel blood anticoagulants

N-(Carboxymethyl)chitosan was subjected to sulfation in a mixture of concentrated sulfuric acid (oleum) and N,N-dimethylformamide, under anhydrous conditions. The resulting product contained 11% of sulfur and degree of substitution: N-acetyl, 42%; N-carboxymethyl, 58%; and sulfate, 100%. Sonication of the sulfated N-(carboxymethyl)chitosan gave two main fractions whose molecular weights were 39,000 and 80,000. In human blood, complexes of sulfated N-(carboxymethyl) chitosan and antithrombin inhibited both thrombin and factor Xa, and produced neither hemolysis nor alterations in erythrocytes and lymphocytes. Sulfated N-(carboxymethyl)chitosan is therefore proposed as a blood anticoagulant.     

Characterization and antimicrobial activity of water-soluble N-(4-carboxybutyroyl) chitosans against some plant pathogenic bacteria and fungi

Water-soluble N-(4-carboxybutyroyl) chitosan derivatives with different degrees of substitution (DS) were synthesized to enhance the antimicrobial activity of chitosan molecule against plant pathogens. Chitosan in a solution of 2% aqueous acetic acid-methanol (1:1, v/v) was reacted with 0.1, 0.3, 0.6 and 1 mol of glutaric anhydride to give N-(4-carboxybutyroyl) chitosans at DS of 0.10, 0.25, 0.48 and 0.53, respectively. The chemical structures and DS were characterized by ¹H and ¹³C NMR spectroscopy, which showed that the acylate reaction took place at the N-position of chitosan. The synthesized derivatives were more soluble than the native chitosan in water and in dilute aqueous acetic acid and sodium hydroxide solutions. The antimicrobial activity was in vitro investigated against the most economic plant pathogenic bacteria of Agrobacterium tumefaciens and Erwinia carotovora and fungi of Botrytis cinerea, Pythium debaryanum and Rhizoctonia solani. The antimicrobial activity of N-(4-carboxybutyroyl) chitosans was strengthened than the un-modified chitosan with the increase of the DS. A compound of DS 0.53 was the most active one with minimum inhibitory concentration (MIC) of 725 and 800 mg/L against E. carotovora and A. tumefaciens, respectively and also in mycelial growth inhibiation against B. cinerea (EC₅₀ = 899 mg/L), P. debaryanum (EC₅₀ = 467 mg/L) and R. solani (EC₅₀ = 1413 mg/L).     

Structural and mechanistic studies on N-(2-carboxyethyl)arginine synthase

N²-(2-Carboxyethyl)arginine synthase (CEAS), an unusual thiamin diphosphate (ThDP)-dependent enzyme, catalyses the committed step in the biosynthesis of the β-lactamase inhibitor clavulanic acid in Streptomyces clavuligerus. Crystal structures of tetrameric CEAS-ThDP in complex with the substrate analogues 5-guanidinovaleric acid (GVA) and tartrate, and a structure reflecting a possible enol(ate)-ThDP reaction intermediate are described. The structures suggest overlapping binding sites for the substrates d-glyceraldehyde-3-phosphate (d-G3P) and l-arginine, and are consistent with the proposed CEAS mechanism in which d-G3P binds at the active site and reacts to form an α,β-unsaturated intermediate, which subsequently undergoes (1,4)-Michael addition with the α-amino group of l-arginine. Additional solution studies are presented which probe the amino acid substrate tolerance of CEAS, providing further insight into the l-arginine binding site. These findings may facilitate the engineering of CEAS towards the synthesis of alternative β-amino acid products.     

Synthesis and evaluation of N-(4-benzylphenyl)piperazines as VGF inducers

A series of compounds was discovered that induce the production of VGF mRNA in SH-SY5Y cells and exhibit cytoprotection under tunicamycin induced endoplasmic reticulum (ER) stress. The aminophenol ring and linker chain of the template SUN N8075 (1) was modified to yield compounds with higher efficacy and lower propensity for adverse effects.     

Catalysis of ester hydrolysis by N-(2-dimethylaminoethyl)acetohydroxamic acid (I)

N-(2-dimethylaminoethyl)acetohydroxamic acid was synthesized. This compound, which incorporates a dimethylamino group as a second functionality into the hydroxamic acid molecule, catalyzes the hydrolysis of p-nitrophenyl acetate faster than acetohydroxamic acid itself does. The function of the dimethylamino group is to labilize the intermediate formed in the reaction, thus assisting deacylation intramolecularly. The dimethylamino group carries out this function by intramolecular general base catalysis. Nucleophilic catalysis is ruled out by the sizable deuterium oxide solvent isotope effect () found. General acid-hydroxide ion catalysis is ruled out by determination of the lack of reaction with azide ion, which does not possess a dissociable proton, with the intermediate in this reaction. The deuterium oxide solvent isotope effect on the azide ion reaction of the intermediate also rules out a general acid-hydroxide ion reaction.     

Novel hydrogel obtained by chitosan and dextrin-VA co-polymerization

A novel hydrogel was obtained by reticulation of chitosan with dextrin enzymatically linked to vinyl acrylate (dextrin-VA), without cross-linking agents. The hydrogel had a solid-like behaviour with G′ (storage modulus) >> G″ (loss modulus). Glucose diffusion coefficients of 3.9 × 10⁻⁶ ± 1.3 × 10⁻⁶ cm²/s and 2.9 × 10⁻⁶ ± 0.5 × 10⁻⁶ cm²/s were obtained for different substitution degrees of the dextrin-VA (20% and 70% respectively). SEM observation revealed a porous structure, with pores ranging from 50 μm to 150 μm.     

Novel complex hydrogels based on N-carboxyethyl chitosan and quaternized chitosan and their controlled in vitro protein release property

A novel pH-responsive hydrogel (CHC) composed of N-carboxyethyl chitosan (CEC) and N-[(2-hydroxy-3-trimethylammonium) propyl] chitosan chloride (HTCC) was synthesized by the redox polymerization technique. Turbidimetric titrations were used to determine the stoichiometric ratio of these two chitosan derivatives. The hydrogel was characterized by FT-IR, thermal gravimetric analysis (TGA), X-ray diffractometry (XRD), and scanning electron microscopy (SEM). The dynamic transport of water showed that the hydrogel reached equilibrium within 48 h. The swelling ratio of CHC hydrogel depended significantly on the pH of the buffer solution. The performance of the CHC as a matrix for the controlled release of BSA was investigated. It was found that the release behavior was determined by pH value of the medium as well as the intermolecular interaction between BSA and the hydrogels.     

Synthesis and activity of di- or trisubstituted N-(phenoxyalkyl)- or N-{2-[2-(phenoxy)ethoxy]ethyl}piperazine derivatives on the central nervous system

Aim of the study was evaluation of anxiolytic, antidepressant, anticonvulsant and analgesic activity in a series of a consistent group of compounds. A series of eleven new N-(phenoxyalkyl)- or N-{2-[2-(phenoxy)ethoxy]ethyl}piperazine derivatives has been obtained. Their affinity towards 5-HT_1A, 5-HT_2A, 5-HT₆, 5-HT₇, D₂ and α₁ receptors has been assessed, and then functional assays were performed. The compounds were evaluated in mice, i.p. for their antidepressant-like (forced swim test), locomotor, anxiolytic-like (four-plate test) activities as well as – at higher doses – for anticonvulsant potential (MES) and neurotoxicity (rotarod). Two compounds (3, 6) were also evaluated for their analgesic activity in neuropathic pain models (streptozocin test, oxaliplatin test) and they were found active against allodynia in diabetic neuropathic pain at 30?mg/kg. Among the compounds, anxiolytic-like, anticonvulsant or analgesic activity was observed but antidepressant-like activity was not. One of the two most interesting compounds is 1-{2-[2-(2,4,6-trimethylphenoxy)ethoxy]ethyl}-4-(2-methoxyphenyl)piperazine dihydrochloride (9), exhibiting anxiolytic and anticonvulsant activity in mice, i.p. 30 min after administration (at 2.5?mg/kg and ED₅₀?=?26.33?mg/kg, respectively), which can be justified by the receptor profile: 5-HT_1A K_i?=?5?nM (antagonist), 5-HT₇ K_i?=?70?nM, α₁ K_i?=?15?nM, D₂ K_i?=?189?nM (antagonist). Another interesting compound is 1-[3-(2,4,6-trimethylphenoxy)propyl]-4-(4-methoxyphenyl)piperazine dihydrochloride (3), exhibiting anxiolytic, anticonvulsant and antiallodynic activity in mice, i.p., 30?min after administration (at 10?mg/kg, ED₅₀?=?23.50?mg/kg, at 30?mg/kg, respectively), which can be related with 5-HT_1A weak antagonism (K_i?=?146?nM), or other possible mechanism of action, not evaluated within presented study. Additionally, for the most active compound in the four-plate test (7), molecular modeling was performed (docking to receptors 5-HT_1A, 5-HT_2A, 5-HT₇, D₂ and α_1A).     

The nonmicrosomal production of N-(4-chlorophenyl)-glycolhydroxamic acid from 4-chloronitrosobenzene by rat liver homogenates

The incubation of 4-chloronitrosobenzene (4-CNB) with subcellular fractions of rat liver resulted in the formation of a previously unknown type of hydroxamic acid metabolite for mammals. This new metabolite, N-(4-chlorophenyl)glycolhydroxamic acid (Gl-CHA), is most likely formed through the action of liver transketolase on the substrate 4-CNB. Gl-CHA was produced only by the 10 000g and 105 000g supernatant fractions, and required glucose-6-phosphate as an energy source. No hydroxamic acid metabolites were produced in detectable quantities by the microsomal fraction of the rat liver homogenate. Gl-CHA was positively identified by isolation and comparison to an authentic sample of Gl-CHA. Authentic Gl-CHA was prepared by the condensation of 4-chlorophenylhydroxylamine with glycolic acid in the presence of dicylohexylcarbodiimide. The highest observed conversion of 4-CNB to Gl-CHA was 18%, which occurred at the lowest concentration of 4-CNB incubated with the 105 000g supernatant. Gl-CHA was not produced by C-hydroxylation of the corresponding acetyl-derived hydroxamic acid, since none of the subcellular fractions of rat liver would effect this conversion. The incubation of 4-chloroaniline under identical conditions failed to result in the production of Gl-CHA; however, such an observation is probably not important to the possibility that Gl-CHA might be a significant metabolite in vivo.     

Synthesis and characterization of an N-coordinated amidate copper(II) complex of deprotonated N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide

The title ligand, N-(2,6-diisopropylphenyl)-2-(bis-(2-pyridylmethyl))aminoethanamide (DIPMAE-H), was prepared by a nucleophilic substitution reaction between N-(2,6-diisopropyl)phenyl-2-bromoethanamide and bis-(2-pyridylmethyl)amine. An analogous ligand (TBPMAE-H) in which the 2,6-diisopropylphenyl group was substituted for a tert-butyl group was also prepared in this manner. Then, [(DIPMAE-H)CuBr]⁺Br⁻ and [(TBPMAE-H)CuBr]⁺Br⁻ were prepared by heating one equivalent of ligand and CuBr₂ in CH₃CN. In both compounds the geometry about the copper center is square pyramidal with distortions due to the geometrical constraints of the ligand. The amide oxygen occupies the axial position, and the three amine nitrogens and the bromide ligand form the basal plane of the square pyramid. Pairs of complexes in the unit cell are associated via weak donation of a lone pair on the bromide ligand of one complex to the copper center of another (Cu?Br distances in the range of 3.3576-3.4022 Å).The title compound, (DIPMAE)CuBr, was prepared by deprotonation of [(DIPMAE-H)CuBr]⁺Br⁻ using NaH. The key feature of (DIPMAE)CuBr is the amidate group η¹- and N-coordinated to the copper center. The compound also exhibits distorted trigonal bipyramidal coordination geometry with the bromide and tertiary amine donors occupying the axial sites and the amidate and pyridyl donors occupying the equatorial positions. The copper atom is displaced from the trigonal plane towards the bromide donor apex due to the geometrical demands of the ligand.     

Synthesis and characterization of gallium complexes bearing N-arylmethylenethiobenzahydrazone ligands; crystal structure of diethyl[N-(4-N,N-dimethylamino)benzylidene thiobenzahydrazonato]gallium

Five diethylgallium complexes of type Et₂GaL [(L = N-(4-methoxy) benzylidenethiobenzahydrazonato (1), N-(3,4-dimethoxy)benzylidenethio benzahydrazonato (2), N-(4-N,N-dimethylamino)benzylidenethiobenza hydrazonato (3), N-(2-naphthyl)methylenethiobenzahydrazonato (4), N-(9-anthryl)methylenethiobenzahydrazonato (5)] have been synthesized by the reaction of triethylgallium with appropriate N-arylmethylene thiobenzahydrazones. The compounds obtained have been characterized by elemental analysis, ¹H NMR, IR and mass spectroscopies, respectively. The solid structure of 3 has been determined by X-ray single crystal analysis, in which Ga atom is four coordinate. The photoluminescent property of complex 1 was studied. The maximum emission wavelength is 475 nm upon radiation by UV light.     

Coordination modes of N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine with copper (I) and (II) halides

The title ligand, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine, was prepared via a condensation-reduction synthetic route. The compounds, CuCl(C₁₉H₁₉N₃O) and [CuBr(C₁₉H₁₉N₃O)]⁺Br⁻ · 3H₂O, were readily synthesized from the reaction of CuCl or CuBr₂ and the ligand in acetonitrile. The title copper(I) compound is an O-H ? Cl hydrogen-bonded linear chain of tetrahedrally coordinated copper centers, and the title copper(II) compound exists as two strongly tetragonally distorted dibromide bridged metal cations in a dimer with the phenol hydroxyl groups weakly bound in a trans-fashion to one of the bridging bromides. In the copper(I) complex the phenoxy group acts only as a hydrogen bond donor, whereas in the copper(II) complex it acts both as a ligand and a hydrogen bond donor.     

Syntheses, structures and properties of copper(II) complexes containing N-(2-hydroxybenzyl)-amino amide ligands

Four copper(II) complexes containing the reduced Schiff base ligands, namely, N-(2-hydroxybenzyl)-glycinamide (Hsglym) and N-(2-hydroxybenzyl)-l-alaninamide (Hsalam) have been synthesized and characterized. The crystal structures of [Cu₂(sglym)₂Cl₂] (1), [Cu₂(salam)₂(NO₃)₂] · H₂O (3), [Cu₂(salam)₂(NO₃)(H₂O)](NO₃) · 1.5H₂O (4), [Cu₂(salam)₂](ClO₄)₂ · 2H₂O (5) show that the Cu(II) atoms are bridged by two phenolato oxygen atoms in the dimers. The sglym ligand bonded to Cu(II) in facial manner while salam ligand prefers to bind to Cu(II) in meridonal geometry. Variable temperature magnetic studies of 3 showed it is antiferromagnetic. These Cu(II) complexes and [Cu₂(sglym)₂(NO₃)₂] (2), exhibit very small catecholase activity as compared to the corresponding complexes containing acid functional groups.     

Development of N,O-(carboxymethyl)chitosan/collagen matrixes as a wound dressing

In an attempt to accelerate wound healing by stimulating the recruitment of fibroblasts and improve the mechanical properties of collagen matrixes, N,O-(carboxymethyl)chitosan (NOCC) was incorporated into the backbone of a collagen (COL) matrix without or with chondroitin sulfate (CS) or an acellular dermal matrix (ADM). The result of a cell migration study demonstrated that the migration of fibroblasts was significantly enhanced by NOCC in a concentration-dependent manner. In the analysis with a dynamic mechanical analyzer, NOCC/CS/COL matrixes presented higher tensile strengths than did NOCC/ADM/COL matrixes. Skin fibroblasts cultured on the matrixes containing NOCC showed increased proliferation and secretion of three kinds of cytokines compared with the control. Results of the in vivo wound healing study showed that matrixes incorporating NOCC showed markedly enhanced wound healing compared with the control. Therefore, the above results clearly suggest that NOCC/COL matrixes containing CS or ADM can be potential wound dressings for clinical applications.     

Preparation and properties of alginate/carboxymethyl chitosan blend fibers

Alginate/carboxymethyl chitosan blend fibers, prepared by spinning their mixture solution through a viscose-type spinneret into a coagulating bath containing aqueous CaCl₂, were studied for structure and properties with the aid of infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron micrography (SEM). The analyses indicated a good miscibility between alginate and carboxymethyl chitosan, because of the strong interaction from the intermolecular hydrogen bonds. The best values of the dry tensile strength and breaking elongation were obtained when carboxymethyl chitosan content was 30 and 10 wt%, respectively. The wet tensile strength and breaking elongation decreased with the increase of carboxymethyl chitosan content. Introduction of CM-chitosan in the blend fiber improved water-retention properties of blend fiber compared to pure alginate fiber. Antibacterial fibers, obtained by treating the fibres with aqueous solution of N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride and silver nitrate, respectively, exhibited good antibacterial activity to Staphylococcus aureus.     

New syntheses of N-(guanosin-8-yl)-4-aminobiphenyl and its 5′-monophosphate

N-Acetoxy-4-trifluoroacetylaminobiphenyl (N-acetoxy-TFAABP) reacted readily with Guo and GMP at neutrality in a one-step fashion to yield N-(guanosin-8-yl)4-aminobiphenyl (Guo-ABP) (I) and N(guanosin-8-yl)-4-aminobiphenyl-5′-monophosphate (GMP-ABP) (II), respectively.GMP-ABP could also be formed in much lower yield from the reaction of N-acetoxy-4-formylaminobiphenyl (N-acetoxy-FABP) with GMP (pH 7.0) under more rigorous conditions.Enzymatic hydrolysis of GMP-ABP with alkaline phosphatase in Tris buffer (pH 8.0) at 37°C yielded Guo-ABP.Guo-ABP showed a brilliant blue fluorescence on exposure to 366 nm UV light and its UV absorption spectrum was identical to that of Guo-ABP prepared by Kriek via a different route. Elemental analysis and nuclear magnetic resonance (NMR) data further confirmed the identity of this compound.     

N-(β-iodoethy)trifluoroacetamide: A new reagent for the aminoethylation of thiol groups in proteins

β-Iodoethyltrifluoroacetamide was prepared and evaluated for use in the aminoethylation of sulfhydryl groups in proteins. Lysozyme, ribonuclease A, chymotrypsinogen A, and soybean trypsin inhibitor were reduced using dithiothreitol in 6 m guanidine hydrochloride. The reduced proteins were then treated with the reagent. Conversion of cysteinyl to aminoethylcysteinyl residues averaged 97%; no destruction of nontarget residues was observed.