Preparation of sugarcane bagasse hemicellulosic succinates using NBS as a catalyst

The chemical modification of native sugarcane bagasse hemicelluloses with succinic anhydride using N-bromosuccinimide as a catalyst and N,N-dimethylacetamide/lithium chloride system as solvent was studied. The parameters optimised included succinic anhydride concentration by the molar ratio of succinic anhydride/anhydroxylose units in native hemicelluloses from 1:1 to 9:1, reaction time 0.5–6 h, NBS concentration 0.5–3.0%, and reaction temperature 25–85 °C required in the process. Results were also compared with other catalysts such as pyridine, DMAP, H₂SO₄, and other two tertiary amine catalysts, N-methyl pyrrolidine, and N-methyl pyrrolidinone. The degree of substitution of succinylated hemicelluloses ranged between 0.19 and 1.39, depending on the experimental conditions. FT-IR and ¹H and ¹³C NMR spectroscopic characterization of the esterified polymers indicated a monoester substitution. The thermal stability of the succinylated hemicelluloses decreased upon chemical modification.     

Interaction of oxidized and reduced N-methylphenazonium methosulfate (PMS) with Photosystem II

In 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) poisoned chloroplasts, the restoration of the fluorescence induction is presumed to be due to a back reaction of the reduced primary acceptor (Q⁻) and the oxidized primary donor (Z⁺) of Photosystem II. Carbonylcyanide m-chlorophenylhydrazone (CCCP) is known to inhibit this back reaction. The influence of reduced N-methylphenazonium methosulfate (PMS) in the absence of CCCP and of oxidized PMS in the presence of CCCP on the back reaction was investigated and the following results were obtained:

1. (1) Reduced PMS at the concentration of 1 μM inhibits the back reaction as effectively as hydroxylamine, suggesting an electron donating function of reduced PMS for System II.

2. (2) The inhibition of the back reaction by CCCP is regenerated to a high degree by oxidized PMS which led to assume a cyclic System II electron flow catalysed by PMS.

3. (3) At concentrations of reduced PMS higher than 1 μM it is shown that both the fast initial emission and more significantly the variable emission are quenched.

Potential roles of hypochlorous acid and N-chloroamines in collagen breakdown by phagocytic cells in synovitis

We have tested the effects of the neutrophil/macrophage products, hypochlorous acid (HOCl) and N-chloroamines, on the structural integrity and proteolytic susceptibility of collagen to determine if these agents could play a role in inflammatory joint destruction. Rates of HOCl reaction with collagen, and collagen gelation were monitored by spectrophotometric methods. Direct fragmentation, and degradation by collagenase were measured by the release of acid-soluble counts from ³H-collagen. Physiologically relevant concentrations of HOCl (5–50 μM) reacted rapidly and quantitatively at several sites in the collagen polypeptide chain, causing extensive protein fragmentation and preventing collagen gelation. In contrast, reaction with (5–50 μM) N-chloroalanine induced little direct collagen fragmentation. Oxidative damage by N-chloroamines was, however, evident because collagen displayed greatly increased proteolytic susceptibility following N-chloroamine treatment. Collagen degradation by collagenase increased as much as 3-fold after exposure to N-chloroamine treatment. Collagen degradation by collagenase increased as much as 3-fold after exposure to N-chloroalanine. N-chloroleucine caused a small increase in proteolytic susceptibility, but N-chlorotaurine had no effect. Collagen fragmentation by HOCl, inhibition of gelation by HOCl, and N-chloroalanine-induced proteolytic susceptibility, all increased with linear kinetics at oxidant concentrations of 5 μM to 1.0 mM. In synovitis, phagocytes expose collagen to HOCl, N-chloroamines, and collagenase. It is known that HOCl can activate neutrophil procollagenase. Based on our new findings, we propose a model of inflammatory joint destruction that also includes collagen fragmentation, and increased susceptibility of collagen to degradation by collagenase. It may also be possible that taurine exerts a protective effect against HOCL/OCL⁻ damage by reacting to form what appears to be essentially an inert N-chloroamine. The validity of this model must now be tested.     

Naphthalene-dioxygenase-catalysed cis-dihydroxylation of azaarene derivatives: Part 1: 2-Pyridones and 2-quinolones

The scope of the biotransformation of 2-pyridone- and 2-quinolone-derived compounds by recombinant whole-cells of E. coli JM109(DE3)(pDTG141) expressing the naphthalene-dioxygenase system from Pseudomonas sp. NCIB 9816-4 was explored, using a series of N- and C-substituted derivatives. Among them, only the N-methyl substituted compounds were good substrates for a regio- and stereoselective dihydroxylation reaction leading to cis-dihydroxydihydro pyridone derivatives, corresponding to the general pattern expected for this enzyme. In the absence of dihydroxylation reactions, N-dealkylations and monohydroxylations on external methyl groups were observed.     

A novel one-pot three-component reaction: synthesis of triheterocyclic 4H-pyrimido[2,1-b]benzazoles ring systems

A novel one-pot three-component condensation reaction of an aldehyde, β-ketoester and 2-aminobenzimidazole or 2-aminobenzothiazole in 1,1,3,3-N,N,N′,N′-tetramethylguanidinium trifluoroacetate as an ionic liquid is described. During the course of this reaction 4H-pyrimido[2,1-b]benzimidazoles or 4H-pyrimido[2,1-b]benzothiazoles are formed in high yields at 100 °C. The ionic liquid can be recovered conveniently and reused efficiently.     

Menadiol as an electron donor for reversed oxidative phosphorylation in submitochondrial particles

Dithiothreitol in the presence of menadione or N,N,N′,N′-tetramethyl-p-phenylenediamine provides the reducing equivalents for oxidative phosphorylation and the ATP-dependent reduction of NAD⁺ in submitochondrial particles. With menadione the reaction is nearly as fast as with succinate and it is insensitive to antimycin, indicating electron entry between the first and second sites of oxidative phosphorylation. The phenylenediamine-mediated reduction of NAD⁺ is nearly as fast as succinate-linked reduction and is antimycin sensitive.     

The Feulgen Reaction After Hydrolysis at Room Temperature

Among the cytochemical methods for demonstrating desoxyribonucleic acid, the hydrochloric-acid-Schiif reaction has been valuable since Feulgen reported it in 1924. A difficulty in that technic is that the section may come loose from the slide; this is caused by hydrolysis at 60° C. When sections were hydrolyzed by 1, 3, 5 or 6 N HCl at room temperature for 15 minutes, adequate hydrolysis and the strong development of color occurred with 5 N HCl. Similarly successful results were obtained with 5 N nitric acid hydrolysis for 10 minutes. Both procedures appear to be as practical as hydrolysis in 1 N HCl at 60° for 4-6 minutes.     

Synthetic routes to mono-N-functionalized P2N2-ligands

Three different synthetic routes have been explored for the synthesis of the mono-N-substituted phosphinoamine N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine: (a) selective alkylation of N,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (b) linkage of the different fragments of N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (c) selective acylation of N,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine followed by acetyl reduction. While approaches (a) and (b) were unsuccessful, N-ethyl,N′bis[2(diphenylphosphino)phenyl]propane-1,3-diamine was obtained by route (c) via separation of the mono- and di-alkylated P₂N₂-species obtained from reduction, through complexation of Ni(NO₃)₂6H₂O followed by demetallation reaction with KCN. Additional related phosphinoamine chelates and phosphonium adducts were synthesized and characterized by conventional physico–chemical techniques.     

Succinoylation of sago starch in the N,N-dimethylacetamide/lithium chloride system

The modification reaction of sago starch with succinic anhydride (SA) using pyridine (PY) and/or 4-dimethyaminopyridine (DMAP) as catalyst and N,N-dimethylacetamide (DMA)/lithium chloride (LiCl) system as solvent was studied. A series of succinylated starch derivatives were prepared with a degree of substitution (DS) ranging from 0.14 to 1.54. The structure of the resulting polymers determined by means of ¹³C NMR spectroscopy indicated that substitution preferably occurs at the C₂ and C₆ hydroxyl groups. The thermal stability of the material was decreased by chemical modification. Effects of reactant molar ratio, reaction time, and the concentrations of DMAP and LiCl on the reaction efficiency are discussed.     

Synthesis of methylated chitosan containing aromatic moieties: Chemoselectivity and effect on molecular weight

N-Arylated chitosans were synthesized via Schiff bases formed by the reaction between the primary amino group of chitosan with aromatic aldehydes followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Treatment of chitosan containing N,N-dimethylaminobenzyl and N-pyridylmethyl substituents with iodomethane under basic conditions led to quaternized N-(4-N,N-dimethylaminobenzyl) chitosan and quaternized N-(4-pyridylmethyl) chitosan. Methylation occurred at either N,N-dimethylaminobenzyl and N-pyridylmethyl groups before the residual primary amino groups of chitosan GlcN units were substituted. The total degree of quaternization of each chitosan varied depending on the extent of N-substitution (ES) and the sodium hydroxide concentration used in methylation. Increasing ES increased the total degree of quaternization but reduced attack at the GlcN units. N,N-dimethylation and N-methylation at the primary amino group of chitosan decreased at higher ES’s. Higher total degrees of quaternization and degrees of O-methylation resulted when higher concentrations of sodium hydroxide were used. The molecular weight of chitosan before and after methylation was determined by gel permeation chromatography under mild acidic condition. The methylation of the N,N-dimethylaminobenzyl derivative with iodomethane was accompanied by numerous backbone cleavages and a concomitant reduction in the molecular weight of the methylated product was observed. The antibacterial activity of water-soluble methylated chitosan derivatives was determined using Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria; minimum inhibitory concentrations (MIC) of these derivatives ranged from 32 to 128 μg/mL. The presence of the N,N-dimethylaminobenzyl and N-pyridylmethyl substituents on chitosan backbone after methylation did not enhance the antibacterial activity against S. aureus. However, N-(4-N,N-dimethylaminobenzyl) chitosan with degree of quaternization at the aromatic substituent and the primary amino group of chitosan of 17% and 16–30%, respectively, exhibited a slightly increased antibacterial activity against E. coli.     

Synthesis and antimicrobial activity of 5-hydroxymethyl- 8-methyl-2-(N-arylimino)-pyrano[2,3-c]pyridine-3-(N-aryl)-carboxamides

Several novel 2-imino-5-hydroxymethyl-8-methyl-2H-pyrano[2,3-c]pyridine-3-(N-aryl) carboxamides were prepared by reaction of pyridoxal hydrochloride with various N-arylcyanoacetamides. Reaction of these compounds with aromatic amines furnished a wide series of 2-(N-R-phenyl) imino-5-hydroxymethyl-8-methyl-2H-pyrano[2,3-c]pyridine-3-carboxamides. Antibacterial and antifungal activities of the synthesized compounds were studied. Most of the obtained compounds demonstrated significant activity against bacterial or fungal strains (MIC in the range of 12.5–25 μg/mL), displaying comparable or even better efficacy than the standard drugs.     

Synthesis of novel vasodilatory active nicotinate esters with amino acid function

A variety of N-[(ethyl-4,6-diaryl-3-pyridinecarboxylate)-2-yl]amino acid esters 6a–h were synthesized through the reaction of 2-bromonicotinates 4 with a number of primary amino acid ester hydrochlorides 5 in refluxing tetrahydrofuran in the presence of triethylamine as dehydrohalogenating agent. Similarly, reaction of 4 with N-glycylglycine ethyl ester hydrochloride 7 ‘as a representative example of dipeptide derivative’ afforded smoothly the corresponding N-[(ethyl-4,6-diaryl-3-pyridinecarboxylate)-2-yl]-N′-glycylglycine ethyl ester analogues 8. However, reaction of 4 with 5 in refluxing pyridine yielded the unexpected 2-aminonicotinate esters 9. Vasodilation activity screening for the synthesized nicotinate esters was investigated in vitro on the contractile response of vascular thoracic aorta smooth muscle from Wistar rats, where all the tested compounds exhibit considerable vasodilatory properties. In addition, few prepared compounds especially, 6b, 6h and 9b reveal remarkable vasodilation potency (IC₅₀).     

1-Alkyl-3-amino-5-aryl-1H-[1,2,4]triazoles: novel synthesis via cyclization of N-acyl-S-methylisothioureas with alkylhydrazines and their potent corticotropin-releasing factor-1 (CRF(1)) receptor antagonist activities.

Cyclizations of alkylhydrazines with N-acyl-S-methylisothioureas, readily synthesized from acyl chlorides, sodium thioisocyanate, dialkylamines then methyl iodide in a one-pot reaction, gave 1-alkyl-3-dialkylamino-5-phenyltriazoles 7 as major products. The regioisomers were assigned through the use of NOE NMR experiments. While bearing a N-bis(cyclopropyl)methyl-N-propylamino group, this series of compounds shows very good binding affinity on the human CRF₁ receptor. Among them, 1-methyl-3-[N-bis(cyclopropyl)methyl-N-propylamino]-5-(2,4-dichlorophenyl)-1H-[1,2,4]triazole 7a had the best binding affinity for the CRF₁ receptor (K_i=9 nM).     

Degradation of Hyaluronic Acid, Poly- and Mono-Saccharides, and Model Compounds by Hypochlorite: Evidence for Radical Intermediates and Fragmentation

Degradation of hyaluronic acid by oxidants such as HO^· and HOCl/ClO⁻ is believed to be important in the progression of rheumatoid arthritis. While reaction of hyaluronic acid with HO^· has been investigated extensively, reaction with HOCl/ClO⁻ is less well defined. Thus, little is known about the site(s) of HOCl/ClO⁻ attack, the intermediates formed, or the mechanism(s) of polymer degradation. In this study reaction of HOCl/ClO⁻ with amides, sugars, polysaccharides, and hyaluronic acid has been monitored by UV-visible (220–340 nm) and EPR spectroscopy. UV-visible experiments have shown that HOCl/ClO⁻ reacts preferentially with N-acetyl groups. This reaction is believed to give rise to transient chloramide (R—NCl—C(O)—R′) species, which decompose rapidly to give radicals via either homolysis (to produce N· and Cl·) or heterolysis (one-electron reduction, to give N· and Cl⁻) of the N—Cl bond. The nature of the radicals formed has been investigated by EPR spin trapping. Reaction of HOCl/ClO⁻ with hyaluronic acid, chondroitin sulphates A and C, N-acetyl sugars, and amides gave novel, carbon-centered, spin adducts, the formation of which is consistent with selective initial attack at the N-acetyl group. Thus, reaction with hyaluronic acid and chondroitin sulphate A, appears to be localized at the N-acetylglucosamine sugar rings. These carbon-centered radicals are suggested to arise from rapid rearrangement of initial nitrogen-centered radicals, formed from the N-acetyl chloramide, by reactions analogous to those observed with alkoxyl radicals. The detection of increasing yields of low-molecular-weight radical adducts from hyaluronic acid and chondroitin sulphate A with increasing HOCl/ClO⁻ concentrations suggests that formation of the initial nitrogen-centered species on the N-acetylglucosamine rings, and the carbon-centered radicals derived from them, brings about polymer fragmentation.     

Hydrogels of N-acylchitosans and their cellulose composites generated from the aqueous alkaline solutions

Hydrogels of N-acetyl and N-propionylchitosans were prepared form aqueous solutions of sodium N-acylchitosan salts (alkaline N-acylchitosans) and sodium N-acylchitosan xanthate [O-(sodium thio)thiocarbonyl N-acylchitosan], respectively, by standing at room temperature and on heating. Novel hydrogels of N-acetylchitosan-cellulose and N-propionylchitosan-cellulose composites were also prepared from sodium cellulose xanthate [O-(sodiumthio)thiocarbonyl cellulose] solutions mixed with sodium N-acylchitosan salts and with sodium N-acylchitosan xanthates, respectively.     

Preparation, spectral characterization, cytotoxic and thermal studies of platinum (IV) thiohydrazone complexes

Platinum (IV) complexes of type [Pt(L)₂Cl₂] [where, L=benzaldehyde-N,N-diphenyl-N-thiohydrazone (L¹), salicylaldehyde-N,N-diphenyl-N-thiohydrazone (L²), acetaphenone-N,N-diphenyl-N-thiohydrazone (L³) and cyclohexanone-N,N-diphenyl-N-thiohydrazone (L⁴)] have been synthesized. The thiohydrazones can exist as thione–thiol tautomer and coordinates as a bidentate N–S ligand. The ligands found to act in monobasic bidentate fashion. Analytical data reveals that metal to ligand stoichiometry is 1:2. The complexes have been characterized by elemental analysis, IR, mass, electronic, ¹H NMR spectroscopic studies, and TG/DTA study. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (E_a), apparent activation entropy (S^#) and heat of reaction (ΔH) have also been carried out for one complex. Cytotoxic study has also been carried out for one complex.     

Amidation of highly methoxylated citrus pectin with primary amines

Partially amidated pectin derivatives (N-alkyl pectinamides) were prepared from highly methoxylated citrus pectin by treatment with different primary amines in methanol. The characterisation of reaction products was made by elemental analysis, photometry and diffuse reflectance FTIR spectroscopy. N-alkyl pectinamides (secondary amides) had two intense infrared bands (amide I and amide II) shifted to lower wave numbers in comparison with the corresponding bands of commercial amidated pectins (primary amides). In some cases aminolysis of HM pectin caused the appearance of infrared bands from N-substituents. Multiple Gaussian decomposition of the characteristic bands in an IR spectrum in the region of 1850–1500 cm⁻¹ were applied for evaluation of the degrees of amidation and methylation. The aminolysis of pectins appears to be an interesting way to produce pectin derivatives with new properties.     

Free radical grafting onto cellulose in homogeneous conditions 1. Modified cellulose–acrylonitrile system

Synthesis of cellulose–polyacrylonitrile copolymers has been studied in a homogeneous solution of N,N-dimethylacetamide/LiCl. The method is based on the preliminary reaction of a portion of OH cellulosic groups with acryloyl chloride to give cellulose with a certain number of pendant double bonds. Successively, acrylonitrile is grafted onto the unsaturated groups by free radical polymerization using azobisisobutyronitrile as initiator. The optimum grafting conditions are evaluated by changing reaction temperature, as well as monomer/initiator and monomer/unsaturated group molar ratios. The products are characterized by size exclusion chromatography, i.r. and ¹³C n.m.r. spectroscopy and a possible reaction mechanism is deduced.     

Kinetics of tributyrin hydrolysis by lipase

The kinetics for the tributyrin hydrolysis using lipase (Pseudomonas fluorscenes CCRC-17015) were investigated in the liquid–liquid and liquid–solid–liquid reaction systems in a batch reactor. The lipase was covalently immobilized onto the surface of porous polymethylacrylamide (PMAA) crosslinking with N,N-methylene biacrylamide with a spacer of ethylenediamine actived by glutaraldehyde. The conditions such as tributyrin concentration, temperature, agitation, and pH value, were evaluated to achieve the optimum reaction conditions for both free lipase and immobilized lipase. The kinetic parameters in the reaction system were also obtained for two reaction systems. The turnover numbers calculated for free lipase and immobilized lipase were 29 and 5.7 s⁻¹, respectively. The parameters of k and k_m obtained using Lineweaver-Burk plot method were 26.2 mol/(mg min) and 1.35 mol/dm³ for free lipase, 5.2 mol/(mg min) and 0.2 mol/dm³ for immobilized lipase, respectively. The experimental results revealed good thermal stability, with greater stability at higher pH value for immobilized lipase in the liquid–solid–liquid reaction.     

Biotransformation of β-amino nitriles: the role of the N-protecting group

N-Tolylsulfonyl- and N-butyloxycarbonyl-protected β-amino nitriles were prepared to study the effect of the N-protecting group on the biotransformation of the β-amino nitriles to the corresponding β-amino amides and acids. The bioconversions were carried out by using whole cells of Rhodococcus sp. R312 and Rhodococcus erythropolis NCIMB 11540. The bioconversion products of five-membered carbocyclic nitriles were mainly the respective acids whereas the carbocyclic six-membered nitriles were accumulated at the stage of the amide. Benefits of the enzymatic compared with the chemical hydrolysis of β-amino nitriles are the mild reaction conditions for the transformation of the nitrile group in the presence of acid or base labile N-protecting groups. In the present work we concentrated on this chemoselectivity of the biotransformation rather than its potential enantioselectivity, which will be subject of future investigations. Thus, some new compounds were prepared: (±)-(2-cyano-cyclohexyl) carbamic acid tert-butyl ester (4a), (±)-(2-carbamoyl-cyclopentyl) carbamic acid tert-butyl ester (3b) and (±)-(2-carbamoyl-cyclohexyl) carbamic acid tert-butyl ester (4b).