Free Phenolic Hydroxyl Research Articles

Antipathogenic Activities and Chemical Composition of Cinnamomum osmophloeum and Cinnamomum zeylanicum Leaf Essential Oils

In this study, inhibitory activities of leaf essential oils from Cinnamomum osmophloeum and Cinnamomum zeylanicum and their major constituents (trans-cinnamaldehyde and eugenol) against Rhizoctonia solani were investigated. Furthermore, the relationship between the antipathogenic activity and the chemical structure of trans-cinnamaldehyde and eugenol is discussed. Results demonstrated that leaf essential oils and their major constituents from C. osmophloeum and C. zeylanicum had strong antipathogenic activities against R. solani. Results obtained from the chemical structure–antipathogenic activity relationship study suggested that trans-cinnamaldehyde or (E)-cinnamic acid with an aldehyde (‒CHO) or an acid (‒COOH) group, a conjugated double bond, and a Length of CH chain outside the ring affect their antipathogenic activity. Furthermore, the presence of the methyl moiety in the ortho position may have a considerable influence on the inhibitory action against R. solani. In addition, compounds with a free phenolic hydroxyl (‒OH) group and a double bond at the C7 position of the phenylpropenes also exhibited potent antipathogenic activity.

Cu(OTf)2-Mediated Chan-Lam Reaction of Carboxylic Acids to Access Phenolic Esters

A Cu(OTf)(2)-mediated Chan-Lam reaction of carboxylic acids with arylboronic acids is described. It represents a facile and practical methodology to access phenolic esters in moderate to good yields. The procedure tolerates a series of functional groups, such as methoxycarbonyl, acetoxy, free phenolic hydroxyl, vinyl, nitro, trifluoromethyl, methoxyl, bromo, chloro, iodo, and acetyl groups.

Isolation and Characterization of Lignin from Tropical and Temperate Hardwood

Dioxane and milled wood lignins (MWL) were isolated from tropical hardwood, Nalita (Trema orientalis) and temperate hardwood, aspen. These lignins were characterized by UV, FTIR, 1H-NMR and 13C-NMR spectroscopy, alkaline nitrobenzene oxidation, molecular weight determination, elemental and methoxyl analysis. The structural analysis revealed that Nalita and aspen lignin is syringyl-guaiacyl type. Aspen lignin had higher syringyl unit than Nalita lignin. The β-O-4 type linkages are the main interunit linkages and more abundant in aspen than Nalita. Dioxane lignin showed higher free phenolic hydroxyl group than MWL in both species. The weight average molecular weight of aspen lignin was lower than that of Nalita lignin. Nalita and aspen lignins contained both erythro and threo configuration, but erythro proton gave stronger peak. A UV absorption maximum of aspen lignin was at 274 nm, whereas it was shifted to 280 nm for Nalita lignin. Keywords: Trema orientalis, Aspen, Dioxane lignin, Milled wood lignin, Syringyl-guaiacyl, β-O-4 linkages DOI: 10.3329/bjsir.v44i3.4399 Bangladesh J. Sci. Ind. Res. 44(3), 271-280, 2009

Methylation of Dietary Flavones Increases Their Metabolic Stability and Chemopreventive Effects

Dietary flavones have promising chemoprotective properties, in particular with regard to cancer, but problems with low oral bioavailability and sometimes unacceptable toxicity have made their use as protective additives to normal diets questionable. However, methylation of free phenolic hydroxyl groups leads to derivatives not susceptible to glucuronic acid or sulfate conjugation, resulting in increased metabolic stability. Methylation also leads to greatly improved transport through biological membranes, such as in intestinal absorption, and much increased oral bioavailability. Recent studies also indicate that methylation results in derivatives with increasing potency to kill cancer cells. They also show high potency towards inhibition of hormone-regulating enzymes, e.g., aromatase, important in the causation of breast cancer. Methylation of the flavones may also result in derivatives with diminished toxic side-effects and improved aqueous solubility. In conclusion, it appears that methylation of dietary flavones as well as of other food products may produce derivatives with much improved health effects.

Resin‐Bound Aminofluorescein for C‐Terminal Labeling of Peptides: High‐Affinity Polarization Probes Binding to Polyproline‐Specific GYF Domains

A polymer support for the solid-phase synthesis of C-terminally labeled carboxylic acids has been developed. Fluorophore-labeled peptides were constructed directly on the amino group of resin-bound aminofluorescein. Fmoc-protected aminofluorescein was coupled onto tritylpolystyrene, and the free phenolic hydroxyl positions of the fluorescein were blocked with suitable protecting groups. The mode of attachment was analyzed and found to be selective for the phenoxy ether linkage. The conditions for peptide synthesis on the labeling resin were investigated, and a small library of C-terminally labeled peptides was prepared. The fluorescence quantum yields of C-terminally labeled peptides were determined and indicated the suitability of the compounds for imaging and binding experiments. The obtained peptides were therefore investigated as fluorescence polarization probes. Two different proline-rich binding domains of the GYF family-CD2BP2 and PERQ2-were targeted by peptides labeled either C- or N-terminally. Reversible binding constants were determined by fluorescence polarization measurements and were verified by competition experiments with the corresponding unlabeled peptide. As a second control, the binding constants were measured by NMR titration experiments, recording the HSQC NMR spectra of (15)N-labeled proteins in the presence of the peptide polarization probes. Ligands with higher affinities than all others known previously were identified for both GYF domains. The competition assay with the developed fluorescent probe has a high statistical reliability and can thus be used for screening of GYF domain inhibitors.

Hydroxycruciforms: Amine‐Responsive Fluorophores

The synthesis of three hydroxy-substituted cruciforms (XF, 1,4-bis(4'-hydroxystyryl)-2,5-bis(4''-methoxyphenylethynyl)benzene, 1,4-bis(4'-methoxystyryl)-2,5-bis(4''-hydroxyphenylethynyl)benzene, and 1,4-bis(4'-hydroxystyryl)-2,5-bis(4''-hydroxyphenylethynyl)benzene) starts with a Horner reaction followed by a Sonogashira coupling and subsequent deprotection. The three herein described XFs contain either two or four free phenolic hydroxyl groups. All three XFs were subjected to photometric UV/Vis titrations in a methanol/water mixture. The respective pK(a) values were obtained by data deconvolution. As the three XFs display a significant change in emission color upon photoinduced deprotonation, the XFs were taken up in different solvents and exposed to twelve amines. The amine-dependent change in emissivity of the tetrahydroxy XF is sufficiently distinct in the eight solvents that all of the inspected amines are discerned by a linear discriminant analysis. The tetrahydroxy XF in different solvents forms a sensor array, the response of which is based on the excited-state proton transfer (ESPT) to amines and mediated by the choice of the battery of solvents that are utilized.

Evolution of the total syntheses of ustiloxin natural products and their analogues.

Ustiloxins A-F are antimitotic heterodetic cyclopeptides containing a 13-membered cyclic core structure with a synthetically challenging chiral tertiary alkyl-aryl ether linkage. The first total synthesis of ustiloxin D was achieved in 31 linear steps using an S(N)Ar reaction. An NOE study of this synthetic product showed that ustiloxin D existed as a single atropisomer. Subsequently, highly concise and convergent syntheses of ustiloxins D and F were developed by utilizing a newly discovered ethynyl aziridine ring-opening reaction in a longest linear sequence of 15 steps. The approach was further optimized to achieve a better macrolactamization strategy. Ustiloxins D, F, and eight analogues (14-MeO-ustiloxin D, four analogues with different amino acid residues at the C-6 position, and three (9R,10S)-epi-ustiloxin analogues) were prepared via the second-generation route. Evaluation of these compounds as inhibitors of tubulin polymerization demonstrated that variation at the C-6 position is tolerated to a certain extent. In contrast, the S configuration of the C-9 methylamino group and a free phenolic hydroxyl group are essential for inhibition of tubulin polymerization.

Isolation and characterization of lignins from Eucalyptus grandis Hill ex Maiden and Eucalyptus globulus Labill. by enzymatic mild acidolysis (EMAL)

Abstract Despite the growing importance of Eucalyptus wood as raw material for pulp and paper, there is a lack of knowledge on the chemistry of their macromolecular components. The present paper addresses this issue by applying the recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) from Eucalyptus grandis, Eucalyptus globulus and the softwood species Douglas fir and white fir, which were used for comparative purposes. The structures of EMALs were investigated by quantitative 31P NMR, DFRC/31P NMR (derivatization followed by reductive cleavage followed by quantitative 31P NMR) and size exclusion chromatography (SEC). Overall, the yields of EMALs isolated from Eucalyptus were higher than those from the softwoods examined. Lignin from E. globulus was found to contain higher contents of arylglycerol-β-aryl ether structures, free phenolic hydroxyl groups and syringyl-type units than lignin from E. grandis. New insights provided by the DFRC/31P NMR revealed that up to 62.2% of arylglycerol-β-aryl ether structures in E. globulus are uncondensed, while in E. grandis the amount of such uncondensed structures was found to be lower than 48%. SEC analyses showed that lignins from E. grandis and softwoods associate in greater extension than lignin from E. globulus.

Studies on curcumin and curcuminoids: XXXI. Symmetric and asymmetric curcuminoids: Stability, activity and complexation with cyclodextrin

A series of curcuminoids, including curcumin, were studied with the main focus on their solubility, phase-distribution, hydrolytic stability and photochemical stability in cyclodextrin (CD) solutions. Their radical scavenging properties were also briefly studied. All the investigated derivatives were more stable towards hydrolytic degradation in CD solutions than curcumin, and the general order of the stabilising effect was HPβCD > MβCD ≫ HPγCD. In contrast, the photochemical studies showed that curcumin is generally more stable than its derivatives. Solubility and phase-distribution studies showed that curcuminoids with side groups on the phenyl moiety have higher affinity for the HPγCD than for the βCDs and that the relative affinity of the larger HPγCD cavity increases with the curcuminoid molecule size. The radical scavenging studies showed that curcumin is more active than the derivatives investigated and that the free phenolic hydroxyl group may be essential for the scavenging properties. This study also indicates that the two halves of the symmetric curcumin molecule act as two separate units and scavenge one radical each.

Structural changes in lignin during the deinking of old newsprint with laccase–violuric acid system

Old newsprint (ONP) could be deinked with laccase–violuric acid system (LVS). To study the mechanism of LVS deinking, lignins from the control and LVS-deinked pulp were isolated and characterized by chemical, spectroscopic and chromatographic methods. The molecular weight change of lignin was tracked by gel permeation chromatogram (GPC), and structural changes in lignin extracted from the control and LVS-deinked pulps were characterized by elemental analysis, functional groups measurement, FT-IR, 1H NMR and 1H– 13C correlation 2D NMR. The experimental results showed that the molecular weight of lignin from LVS-deinked pulp was lower than that of lignin from the control pulp. The contents of free phenolic hydroxyl groups and methoxyl groups of lignin from LVS-deinked pulp decreased, while the contents of carboxyl and carbonyl groups increased. Guaiacyl units in lignin were oxidized by LVS. Stilbene and 5–5′ substructures in lignin were stable to LVS treatment, while β-O-4 and β–β substructures were partially destroyed during the LVS deinking. According to structural changes in lignin, the mechanism of LVS deinking was deduced.

Synthesis of Haptens for Development of Antibodies to Alkylphenols and Evaluation and Optimization of a Selected Antibody for ELISA Development

The development of an enzyme-linked immunosorbent assay (ELISA) based on polyclonal antibodies for a class of endocrine disrupting compounds, 4-nonylphenol, is described. The parent molecule was derivatized at the ortho position of the free phenolic hydroxyl group to obtain the hapten, NP1, and it was conjugated with keyhole limpet hemocyanin, which was used as an immunogen. Four antisera were generated and screened against three coating antigens. The most sensitive ELISA from the screening tests (antiserum NP03As, 1/1000, and coating antigen NP1-BSA, 1 microg/mL) was further optimized and characterized. The influence of various physicochemical factors (organic solvent, pH, ion strength) was investigated. Methanol as the additive organic solvent was found to be the best organic solvent for the ELISA, with optimal sensitivity observed at a concentration of 5%. The ELISA parameters were changed at more acidic or basic pH values, whereas higher ionic strengths strongly suppressed the I(50) value and the maximum absorbance. The most sensitive ELISA for 4-nonylphenol exhibited an I(50) value of 38.6 +/- 5.5 microg/L, with a dynamic range from 12 to 350 microg/L, and the lower limit of detection was 7.7 +/- 1.3 microg/L. The optimized ELISA displayed no significant cross-reaction against the parent compounds, nonylphenol ethoxylates, degradation products, carboxylates, and bisphenol A, except in 4-octylphenol.

Prehydrolysis Sulfite Revisited

AbstractThe prehydrolysis of beech wood in water at different temperatures and the impact of this treatment on further pulping stages were explored. Both, increased condensation degree and an increased number of free phenolic hydroxyl groups were found in the lignin isolated after prehydrolysis. An intermediate alkaline extraction (using either NaOH or MgO as base) following the prehydrolysis was explored. Finally, acid sulfite cooks of the differently pre‐treated materials were performed, and the obtained materials thoroughly analyzed.

Thermal Modifications in Softwood Studied by FT‐IR and UV Resonance Raman Spectroscopies

Scots pine planks were heat‐treated under steam in a temperature range of 100–240°C at every 20°C. Changes in chemical structure of the wood samples were examined with UV resonance Raman (UVRR) and Fourier transform infrared (FT‐IR) spectroscopies. Prior to the FT‐IR and UVRR analysis, the heartwood part of wood samples were ground and extracted with acetone. Both the extracts and the extracted samples were analyzed. In addition, Klason lignin contents of the samples were determined. The FT‐IR and UVRR spectroscopy were powerful techniques to monitor chemical changes in the heat‐treated wood samples. Results confirmed most of what determined previously by other research groups using different techniques. The UVRR and FT‐IR spectra of acetone extracts showed that lignin became partly acetone soluble after a heat treatment of 180°C or greater. Increased levels of free phenolic hydroxyl groups were detected in lignin, probably due to cleavages of β‐O‐aryl ether interunit linkages. The amount of extractable lignin increased with increasing temperature, while the resin in the extracts decreased. UVRR spectra of the wood samples extracted with acetone indicated that the structure of unextractable lignin remained unchanged when heated up to 200°C. Formation of new carbonyl structures was observed in solid wood samples and their extracts. These structures were possibly formed from the degradation products of lignin and hemicelluloses. Lignin content of the samples was increased as a result of degradation of wood hemicelluloses, which started below 200°C.

Solution- and solid-phase synthesis of natural product-like tetrahydroquinoline-based polycyclics having a medium size ring.

A solid-phase synthesis of tetrahydroquinoline-derived polycyclic 4, having a medium size ring with an enamide functionality, was achieved from tetrahydroquinoline derivative 3 in five steps with overall 40-45% yield. An enantiopure, tetrahydroquinoline-derived beta-amino ester, 1, was converted into compound 2 that has a free phenolic hydroxyl group as an anchoring site for solid-phase synthesis. The solid-phase worked well for this sequence, in which the synthesis of the unsaturated eight-membered enamide lactam was obtained by a ring-closing metathesis approach. Compound 4 is a novel, natural product-like polycyclic derivative that could further be utilized in library generation for developing small molecule chemical probes.

Involvement of Reactive Oxygen Species in Capsaicinoid-induced Apoptosis in Transformed Cells

Some varieties of sweet pepper accumulate non-pungent isosters of capsaicin, a type of compounds exemplified by capsiate. The only structural difference between capsaicin and capsiate is the link between the vanillyl and the acyl moieties, via an amide bond in the former and via an ester bond in the latter. By flow cytometry analyses we have determined that nor-dihydrocapsiate, a simplified analogue of capsiate, is a pro-oxidant compound that induces apoptosis in the Jurkat tumor cell line. The nuclear DNA fragmentation induced by nor-dihydrocapsiate is preceded by an increase in the production of reactive oxygen species and by a subsequent disruption of mitochondria transmembrane potential. Capsiate-induced apoptosis is initiated at the S phase of the cell cycle and is mediated by a caspase-3-dependent pathway. The accumulation of intracellular reactive oxygen species in capsiate-treated cells is greatly prevented by the presence of ferricyanide, suggesting that capsiates target a cellular redox system distinct from the one involved in the mitochondrial electron-chain transport. Methylation of the phenolic hydroxyl of nor-dihydrocapsiate completely abrogated the ability to induce reactive oxygen species and apoptosis, highlighting the relevance of the presence of a free phenolic hydroxyl for the pro-oxidant properties of capsaicinoids.

Comparison of quaternary methyl-, ethyl- and butylammonium hydroxides as alkylating reagents in pyrolysis-GC/MS studies of aquatic fulvic acid

Three different tetra-alkylammonium hydroxides (TAAHs) were compared as thermal alkylation reagents in pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) studies of the Nordic reference fulvic acid (NoFA). All the off-line TAAH treatments with tetramethyl- (TMAH), tetraethyl- (TEAH) and tetrabutylammonium hydroxides (TBAH) at 100 °C followed by pyrolysis at 600 °C yielded derivatives of phenols, methoxyphenols and benzenecarboxylic and aliphatic acids as the main products. However, TEAH and TBAH were not capable to alkylate completely all free phenolic hydroxyl groups, which strongly limits their usefulness in determining the original methoxyl and hydroxyl functionalities and leads to underestimation of the general substitution state of aromatic humic constituents. The TEAH and TBAH treatments also yielded lower proportions of polycarboxylic acids as aliphatic products, which is probably due to decarboxylation reactions of different acidic constituents remained nonalkylated during the TAAH treatments. The results imply that the factor limiting most the reactions with different alkylating reagents is not necessarily the applied reagent concentrations but rather their inabilities to reach certain reactive parts of the multi-dimensional macromolecular humic structure. In this respect, TMAH seems to be the most appropriate alkylating reagent for analytical pyrolysis studies of extremely complex and heterogenous humic substances.

Chemical Modification of Chemithermomechanical Pulps Part 1: Mechanical, Optical, and Aging Properties of Propionylated Spruce CTMP

The effect of propionic anhydride on the optical, mechanical, and aging properties of hydrogen-peroxide-bleached spruce (Picea abies) chemithermomechanical pulp (CTMP) has been examined. The aging properties were evaluated using different aging conditions simulating aging behind window-glass, ambient storage (in the dark), and dry heat exposure. The propionylation treatment was carried out on paper sheets. Chemical modification with propionic anhydride strongly reduced light-induced yellowing: Up to 80% of the discoloration (calculated from the post color number) could be hindered, although 50% of the free phenolic hydroxyl groups were still present in the propionylated sample. The stability against storage in the dark under ambient conditions (23°C, 50% relative humidity) or exposure to dry heat (105°C) was, however, not improved to the same extent. Propionylation did not extensively change the optical or dry strength properties of the treated paper sheets, whereas the wet tensile strength was substantially improved.

Copper(I) complexes with N,O-donor Schiff base ligands related to intermediate forms of the TPQ cofactor in amine oxidases

Neutral complexes (PPh3)2Cu(L) were obtained from (PPh3)2Cu(NO3) and the deprotonated forms of the three Schiff base ligands 2-(benzylideneimino)phenol (BimOH), 4-(benzylideneimino)resorcinol (Bim(OH)2) and N-(2,4-dihydroxy-5-isopropylphenyl)acetamide (DipaH3). The ligands were designed to model aminated intermediate forms of the topaquinone (TPQ) cofactor in the enzymatic cycle of copper-dependent amine oxidases. The ligands L are coordinated to the metal centers through imine-N and phenolate-O donor atoms to form five-membered chelate rings, in contrast to the six-membered chelate rings of salen-type Schiff base ligands. Compound (Bim(OH)O)Cu(PPh3)2·0.5CH3OH was structurally analyzed, it exhibits intramolecular aryl–aryl interactions between the ligands and intermolecular hydrogen bonds involving the free phenolic hydroxyl substituent, the coordinated phenolate oxygen atom and the methanol solvate molecule.

Article

The reactivity of lignin model compounds under Mannich conditions with piperidine and formaldehyde was studied. The piperidinomethyl group was confirmed to be introduced quantitatively at sterically unhindered positions ortho to a phenolic hydroxyl when the substrate was allowed to react under ambient conditions. The sequential application of the Mannich reaction followed by quantitative 31P NMR on a variety of lignin samples allowed the amounts of various aromatic groups bearing free phenolic hydroxyls to be determined. More specifically, the technique allowed the quantification of para-hydroxyl phenols, catechols, guaiacols, and phenols bearing C5 or C6 substituents. The quantitative reliability of the technique was also examined with a series of dissolved kraft lignins, isolated at various degrees of delignification. The data were found to favourably compare to those obtained by permanganate oxidation.Key words: lignin, lignin model compounds, Mannich reaction, nuclear magnetic resonance (NMR), phenols, phosphorus, piperidine, quantitative analysis.

Coupling P-31 NMR with the Mannich reaction for the quantitative analysis of lignin

The reactivity of lignin model compounds under Mannich conditions with piperidine and formaldehyde was studied. The piperidinomethyl group was confirmed to be introduced quantitatively at sterically unhindered positions ortho to a phenolic hydroxyl when the substrate was allowed to react under ambient conditions. The sequential application of the Mannich reaction followed by quantitative 31 P NMR on a variety of lignin samples allowed the amounts of various aromatic groups bearing free phenolic hydroxyls to be determined. More specifically, the technique allowed the quantification of para-hydroxyl phenols, catechols, guaiacols, and phenols bearing C5 or C6 substituents. The quantitative reliability of the technique was also examined with a series of dissolved kraft lignins, isolated at various degrees of delignification. The data were found to favourably compare to those obtained by permanganate oxidation.