Methyl Ether Groups Research Articles

Stereoselective Preparation of (E)‐Configured 1,2‐Disubstituted Propenes from Two Aldehydes by a Two‐Carbon Stitching Strategy: Convergent Synthesis of 18,21‐Diisopropyl‐Geldanamycin Hydroquinone and Its C7 Epimer

The title compounds were synthesized in a longest sequence of 27 linear steps and with an overall yield of 2.9 and 3.9%. In the course of the synthesis, two aldehydes representing carbon fragments C1-C7 (Eastern fragment) and C9-C21 (Western fragment) were prepared from D-mannitol, each of which incorporated a key stereogenic center at the respective secondary methyl ether group (C6, C12) from the chiral pool material. The assembly of the two aldehydes was achieved employing α-chloroethyl magnesium chloride as a two-carbon building block. The carbenoid reagent was generated from α-chloroethyl para-tolylsulfoxide by sulfoxide-magnesium exchange and it added smoothly to the highly sensitive aldehyde of the Eastern fragment (C1-C7). Upon oxidation, an α-chloroethyl ketone was generated, which underwent a clean and high-yielding reductive SmI(2) -promoted addition to the other aldehyde fragment. Dehydration delivered the key double bond between C8 and C9 in an overall yield of 72% over four steps. The method was shown to be generally applicable to the racemization-free conversion of several aldehydes into the respective α-chloroethyl ketone (11 examples, 64-95%) and to the coupling protocol (5 examples, 66-90%). The further course of the geldanamycin hydroquinone synthesis included a diastereoselective reduction at C7 and the implementation of the amino group at C20. Since deprotection of the two isopropyl protecting groups could not be achieved in significant yields, the structure of 18,21-diisopropyl-geldanamycin hydroquinone was proven by its independent synthesis from the natural product.

Introduction of Adjacent Oxygen‐Functionalities in Dimethyl Heptalenedicarboxylates

AbstractThe bromination of dimethyl 8‐methoxy‐1,6,10‐trimethylheptalene‐4,5‐dicarboxylate (6; Scheme 2) with N‐bromosuccinimide (NBS) in N,N‐dimethylformamide (DMF) leads in acceptable yields to the corresponding 9‐bromoheptalenedicarboxylate 10 (Table 1). Ether cleavage of 6 with chlorotrimethylsilane (Me3SiCl)/NaI results in the formation of oxoheptalenedicarboxylate 13 in good yield (Scheme 4). The latter can be acetyloxylated to the (acetyloxy)oxoheptalenedicarboxylate 14 with Pb(OAc)4 in benzene (Scheme 5). Oxo derivative 14, in turn, can be selectively O‐methylated with dimethyl sulfate (DMS) in acetone to the (acetyloxy)methoxyheptalenedicarboxylates 15 and 15′ (Scheme 6). The AcO group of the latter can be transformed into a benzyl or methyl ether group by treatment with MeONa in DMF, followed by the addition of benzyl bromide or methyl iodide (cf. Scheme 9). Reduction of the ester groups of dimethyl 7,8‐dimethoxy‐5,6,10‐trimethylheptalene‐1,2‐dicarboxylate (25′) with diisobutylaluminium hydride (DIBAH) in tetrahydrofuran (THF) leads to the formation of the corresponding dimethanol 26′, which can be cyclized oxidatively (IBX, dimethyl sulfoxide) to 8,9‐dimethoxy‐6,7,11‐trimethylheptaleno[1,2‐c]furan (27; Scheme 11).

Controlling the Physical and Electrochemical Properties of Arylamines Through the Use of Simple Silyl Ethers: Liquid, Waxy and Glassy Arylamines

The effect of silyl ether substitution on the physical and electrochemical properties of single and two-nitrogen centered arylamines was explored. It was found that this substitution can significantly lower the Tg and suppress crystallization of these compounds. This resulted in arylamines that were isolated as liquids, waxes, glasses, and in some cases crystalline solids at ambient conditions. Additionally, these silyl ether groups were found to be relatively strong electron donating groups with similar donating potentials to the well known methyl ether group. It is concluded that silyl ether substitution is a synthetic handle to greatly alter the physical properties of arylamines without substantially changing their basic electronic properties.

Extraction of flax shive using sodium ethoxide catalyst in anhydrous ethanol

This work investigated the yield and nature of solvent-soluble organic compounds extracted from flax shive using a room temperature reaction (20 °C) with sodium ethoxide catalyst at four different concentrations (0.2, 0.5, 0.7, and 1.0 M) in anhydrous ethanol. Results were compared with the use of aqueous sodium hydroxide (1.0 M) at two different reaction temperatures (20 °C and 100 °C). Quantitative yield from flax shive varied linearly with sodium ethoxide concentration and averaged 54.5 mg/g on a dry-mass basis (db) at 1.0 M. In contrast, the quantitative yield using 1.0 M sodium hydroxide was much lower, averaging 2.2 mg/g (db). Yield did not differ significantly due to changes of particle size in either case, or due to changes of temperature over the range considered in the case of sodium hydroxide. Analyses using proton nuclear magnetic resonance ( 1H NMR) confirmed all extracts to contain aromatic compounds, thus likely lignin derived, but found differences in chemical characteristics between the two extraction methods. One key difference was the presence of compounds with methyl ether groups in sodium hydroxide extracts that were absent in the case of sodium ethoxide extracts. Given that flax contains a mixed guaiacyl–syringyl lignin, methyl ether groups would be expected to be present. Control reactions on three model compounds were carried out to confirm that transesterification occurred with sodium ethoxide. These control reactions also demonstrated that methyl ether groups would be expected to remain intact under the extraction conditions reported here. In light of the higher yield of solvent soluble compounds recovered by extraction with basic ethanol, flax shive may represent a source of value-added phenolic constituents. This processing method may also represent a useful pre-treatment prior to the production of biofuels by cellulose degrading organisms.

Highly Water-Soluble Neutral BODIPY Dyes with Controllable Fluorescence Quantum Yields

A series of novel highly water-soluble neutral BODIPY dyes have been obtained by functionalization of BODIPY dyes with branched oligo(ethylene glycol)methyl ether groups at positions 8, 2 and 6 or 4 and 4'. Use of an ortho-substituent group of branched oligo(ethylene glycol)methyl ether on the meso-phenyl ring of BODIPY dyes and replacement of the fluorine atoms of BODIPY dyes at positions 4 and 4' with methyloxy or ethynyl subunits significantly enhance fluorescence quantum yields of BODIPY dyes.

Stably dispersible P3HT/ZnO nanocomposites with tunable luminescence by in-situ hydrolysis and copolymerization of zinc methacrylate

Abstract In this paper, the copolymer shell with the internal hydrophobic polymethacrylate layer and the external hydrophilic poly(ethylene glycol) methyl ether groups was successfully bonded on the surface of ZnO nanocrystals through a simple sol–gel method, i.e., radical polymerization of zinc methacrylate (Zn(MA) 2 ) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and hydrolysis. The prepared ZnO@poly(methacrylate-co-poly(ethylene glycol) methyl ether methacrylate) (ZnO@PPEGMA) nanocrystals showed good dispersion and smaller particle size, due to the presence of copolymer shell. The optical properties of ZnO@PPEGMA nanocrystals were characterized by ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) spectroscopy. The results indicated that the absorption edge and PL emission in the UV region of ZnO@PPEGMA nanocrystals appeared obvious blue-shift, due to the smaller particle size. Incorporation of ZnO@PPEGMA nanocrystals into poly(3-hexylthiophene) (P3HT) matrix, the dispersion of P3HT/ZnO@PPEGMA nanocomposites was greatly improved and the nanocomposites possessed excellent photoluminescence stability. Meanwhile, it was observed that the PL emission of P3HT/ZnO@PPEGMA nanocomposites was enhanced significantly, due to the presence of copolymer shell and the improvement of compatibility of ZnO@PPEGMA in the P3HT matrix. The results showed that the P3HT/ZnO@PPEGMA nanocomposites could be potential candidates for optical applications.

Sol-gel reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution

The reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution have been studied by multinuclear magnetic resonance and light scattering techniques. The study has shown that in this peculiar chemical environment the alkoxy groups of 3-glycidoxypropyltrimethoxysilane undergo a fast hydrolysis and condensation which favor the formation of open hybrid silica cages. The silica condensation reaches 90% at a short aging time but does not go to completion even after 9 days. The highly basic conditions also slow down the opening of the epoxies which fully react only after several days of aging. The epoxy opening generates different chemical species and several reaction pathways have been observed; in particular, the formation of polyethylene oxide chains, diols, termination of the organic chain by methyl ether groups and formation of dioxane species. These reactions are slow and proceed gradually with aging; light scattering analysis has shown that clusters of dimensions lower than 20 nm are formed after two days of reactions, but their further growth is hindered by the highly basic conditions which limit full silica condensation and formation of organic chains.

The influence of Metolose structure on the free volume and the consequent metoprolol tartrate release of patches

Matrix-type patches containing Metoprolol tartrate were prepared from two types of Metolose and acrylate polymers. Metolose SM 4000 and Metolose 90SH 100.000SR were applied in different proportions in the patches where the total polymer content was kept constant in each sample. The purpose of the study was to investigate the effect of Metolose structure on the free volume of the patches and the consequent drug release profile. The drug release profiles were characterized by zero-order and first-order models. The results indicate that Metolose, containing hydroxypropyl ether groups and methyl ether groups, enables the formation of H-bonds, thus increasing the free volume holes and the consequent extent and rate of drug release of patches.

Zirconium(IV) Compounds As Efficient Catalysts for Synthesis of α-Aminophosphonates

Zirconium(IV) compounds are reported as excellent catalysts for a three-component one-pot reaction of an amine, an aldehyde or a ketone, and a di/trialkyl/aryl phosphite to form alpha-aminophosphonates under solvent-free conditions at rt. Among the various zirconium compounds, ZrOCl2 x 8 H2O and ZrO(ClO4)2 x 6 H2O were most effective. The reactions were faster with dialkyl/diaryl phosphites than with trialkyl/triaryl phosphites. No O-Me cleavage occurs with aryl methyl ether and methyl ester groups. alpha,beta-Unsaturated carbonyl moiety does not undergo conjugate addition with the phorphorous moiety.

Ring-Modified Analogues and Molecular Dynamics Studies To Probe the Requirements for Fungicidal Activities of Malayamycin A and Its N-Nucleoside Variants

The importance of functional group orientations and the integrity of the bicyclic perhydrofuran core of malayamycin A and two equally active N-nucleoside analogues as fungicides were investigated. Two analogues 10 and 11, representing a THP-truncated and a bicyclic aza-variant, were synthesized and found to be inactive. Molecular dynamics studies on malayamycin A and analogues were performed to highlight the importance of properly orientating the urea and methyl ether groups.

Polysubstituted Isochroman Derivatives with Plant Growth Regulating Properties on Wheat (Triticum aestivum L. cv Klein Escorpion)

The synthesis of isochroman derivatives 4–9 from α-hydroxylactone 3 is reported. These heterocycles, carrying different substituents on C-3, C-4, and C-8, exhibited different degrees of inhibition of the vegetative growth of wheat (Triticum aestivum cv Klein Escorpion) plants, whereas plant developmental patterns such as their protein profile, carotenes/chlorophylls ratio, and weight/length relationship were not significantly affected. Microscopic observation of transverse sections of shoots and roots showed morphological changes in the treated plants, consistent with delayed development. The results suggest that among these isochromans the C-3 carbonyl moiety of the lactone and the C-4 free hydroxyl group are important but not essential for activity, and that a short side chain appended to C-3 is tolerated. However, cleavage of the C-8 methyl ether group to the related free phenol causes a drastic reduction in the growth inhibitory activity.

Optimization of polystyrene-supported triphenylphosphine catalysts for aza-Morita–Baylis–Hillman reactions

A series of polar group functionalized polystyrene-supported phosphine reagents were examined as catalysts in the aza-Morita–Baylis–Hillman reactions of N-tosyl arylimines and a variety of Michael acceptors with the aim of identifying the optimal polymer/solvent combination. For these reactions Janda Jel-PPh 3 (1 mmol PPh 3/g loading) resin containing methoxy groups ( JJ-OMe-PPh 3) on the polystyrene backbone in THF solvent provided the highest yield of all the catalyst/solvent combinations examined. The methyl ether groups were incorporated into JJ-OMe-PPh 3 using commercially available 4-methoxystyrene, and thus such polar polystyrene resins are easily accessible and should find utility as nucleophilic catalyst supports.

Total Synthesis of Dictyodendrin B

A concise total synthesis of dictyodendrin B (1) is reported, a scarce marine alkaloid endowed with promising telomerase inhibitory activity. Key steps of the chosen route are a reductive cyclization of ketoamide 11 to indole 12 mediated by low-valent titanium (from TiCl3 and KC8) followed by a photochemical 6pi-electrocyclization, which was performed in the presence of Pd/C and nitrobenzene to effect concomitant dehydrogenation/aromatization of the product initially formed. Regioselective bromination of the resulting pyrrolocarbazole 13 followed by lithium/bromine exchange and quenching of the resulting organolithium species with p-methoxybenzaldehyde installed the side chain at C2. Oxidation of the benzylic alcohol 15 thus obtained to ketone 17 was best achieved with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine-N-oxide (NMO) in dilute CH2Cl2 solution to avoid the formation of undue amounts of the unsymmetrical dimer 16. Ketone 17 was elaborated into the natural product by selective cleavage of the isopropyl ether with BCl3, introduction of the sulfate moiety with the aid of trichloroethyl chlorosulfuric acid ester, deprotection of all lateral methyl ether groups, and final reductive cleavage of the trichloroethyl ester moiety. The spectroscopic data of synthetic dictyodendrin B thus formed matched those of an authentic sample in all regards. Moreover, it was shown that global deprotection of the peripheral -OH groups in pyrrolo[2,3-c]carbazole 13 is accompanied by spontaneous air-oxidation to form the quinone core of dictyodendrin C.

Water-Soluble Cationic Poly(p-phenyleneethynylene)s (PPEs): Effects of Acidity and Ionic Strength on Optical Behavior

Three cationic PPEs P1‘−P3‘ were obtained through quaternization of their neutral polymers, of which all side chains were respectively featured with a tertiary amino group (P1), an alternative tertiary amino and tri(ethylene glycol)methyl ether group (P2), and an alternative tertiary amino and dodecyloxy group (P3). P1‘ showed intrinsic water-solubility although its quaternization degree was only 45%. Slightly blue-shifted UV−vis absorption maxima in an acidic environment (maximal Δλmax ≈ 3 nm) and obvious red-shifted absorption (maximal Δλmax ≈ 30 nm) and emission maxima (maximal Δλmax ≈ 20 nm) in an alkaline environment at pH < 13 are explained in terms of pH-induced planarization of the conjugated backbone. After the pH was increased to 14, a new absorption (λmax ≈ 478 nm) and emission (λmax ≈ 495 nm) peak appeared in the redder region and the fluorescence intensity further dramatically decreased, implying the occurrence of the conformational change from the planarization of conjugated backbone to the interchain aggregation. The fluorescence enhancement of P1‘ in an acidic environment and the fluorescence decrease of P1‘ in an alkaline environment are attributed to the pH-influenced quenching ability of the nonbonding electron pair on the nitrogen atom, which belongs to the unquaternized tertiary amino group on the side chain, and the interchain aggregation. Such pH-influenced fluorescence intensity can be efficiently buffered by adding salts at pH < 10. Although adding salts in a neutral environment only creates the planarization of PPE conjugated backbone, adding salts in an alkaline environment significantly promotes the formation of interchain aggregation. Amplified quenching of P1‘ by anionic quencher Fe(CN)64- was observed and its Ksv increased significantly after adding salts or increasing pH to 14, for example from Ksv = 9.6 × 105 M-1 at pH = 7 to 7.7 × 106 M-1 at pH = 10 when [NaCl] = 0.1 M, due to the formation of elongated π-conjugation.

A porphyrin dye with monoexponential fluorescence intensity and anisotropy decay behavior in spherical micelles.

A new fluorescent dye based on tetraphenylporphyrin contg. four di(isopropylene glycol)methyl ether groups is used as a micellar probe. The fluorescence lifetime of this porphyrin deriv. is about 10 ns, which is in the order of the rotation time of a micelle. The size of the dye (diam. ca. 37 A) ensures that it perfectly fits into most micelles. The novel fluorophore shows a monoexponential decay both in fluorescence intensity and in anisotropy in solns. of the spherical micelles. The micellar radii deduced with the help of this fluorophore are in excellent agreement with the values inferred from the scattering expts.

Supramolecular ion channels from a transmembrane bischolic acid derivative showing two discrete conductances.

Bischolic acid derivative 1 linked by m-xylylene dicarbamate at the 3,3'-position was synthesized and the single ion channel properties were examined. Compound 1 showed two clearly distinct conductances, 9.5 (type A) and 25.3 pS (type B), under 500 mM KCl symmetric salt conditions, whereas various conductances, ranging from 5-20 pS, were observed in the tetramethylether analogue reported previously. Results indicate that the replacement of four methylether groups with hydroxyls at the 7, 7', 12, and 12' positions in the bischolic acid framework influences the stability of aggregated (supramolecular) ion channel structures. Ion permeability ratios (potassium/chloride and potassium/sodium) for each type of channel were also determined.

Polyether-grafted SnO2 nanoparticles designed for solid polymer electrolytes with long-term stabilityElectronic supplementary information (ESI) available: XPS results and in situ IR spectra. See http://www.rsc.org/suppdata/jm/b4/b405179c/

Polyether-grafted SnO2 nanoparticles are prepared through a hydrothermal method and exchange reactions. X-ray diffraction (XRD) and transmission electron microscopic (TEM) results illustrate that these nanoparticles are uniform, mono-dispersed and about 3 nm in diameter, while thermo-gravimetric and differential thermal analyses (TG-DTA) and infrared (IR) data prove that poly(ethylene glycol methyl ether) (PEGME) groups are bound tightly on SnO2 surfaces. The composites of such PEGME-SnO2 nanoparticles and LiClO4 exhibit ionic conductivity over 10−5 S cm−1, and the PEGME–SnO2–LiClO4 composites act as the main conductive component when PEGME–SnO2 fillers are incorporated in the prototypical PEO–LiClO4 films. The PEO–(PEGME–SnO2)–LiClO4 films exhibit improved conductivities with long-term stability, enhanced Li+ transference numbers and better mechanical properties.

LB film structure of poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)- p-phenylene vinylene) studied by spectroscopy

A PPV derivative, poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)- p-phenylene vinylene), has been synthesized by the Gilch route to study the influence of a long alkyl side chain and a di(ethylene oxide) methyl ether group on the multilayer structure obtained by Langmuir–Blodgett (LB) technique. UV–visible, PL, and FTIR spectra are applied to study the conformation and orientation of the MMDU-PPV molecules in multilayer organization. MMDU-PPV is apt to form a transferable monolayer film, in which the plane of its π system is perpendicular to the air–water interface. The adjacent conjugated main chains of MMDU-PPV in LB films are aligned in parallel fashion and packed with the plane of its π system approximately perpendicular to the layer plane and not organized to compact π-stacking structure for introducing di(ethylene oxide) methyl ether (DEOM) side chains to conjugated main chains. The long alkyl side chains are characterized by all trans-zigzag conformation and average tilt angle of 36±1.5°. The layer-by-layer multilayer of MMDU-PPV obtained by Langmuir–Blodgett technique exhibits some in-plane anisotropy and more pure photoluminescence than that of the dilute MMDU-PPV solution.

Carbon-13 NMR spectroscopic studies on chemically modified and unmodified synthetic and natural humic acids

Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ( 13C-CP/MAS-NMR) was applied to study the chemical modification process of humic acids (HA) with diazomethane and the subsequent alkaline hydrolysis of the methylated HA. This modification process results in HA with selectively blocked phenolic OH groups, which can be used for metal ion binding studies with humic substances. Different chemically modified and unmodified natural and synthetic HA with carbon-13 of natural abundance were investigated. In addition, carbon-13 labeled modified synthetic HA, that were synthesized with [ 13C]diazomethane as methylation reagent, were studied to confirm the assumed modification process and to determine the type of functional groups that have the highest affinity for methylation with diazomethane. The results of the NMR studies with carbon-13 labeled modified HA show that predominantly carboxyl and phenolic OH groups are methylated with diazomethane resulting in methyl ester and methyl ether groups, respectively. Due to the alkaline treatment of the methylated HA, the methyl esters of carboxyl groups are hydrolyzed, whereas methyl ethers of phenolic OH groups remain unchanged, which results in modified HA with blocked phenolic OH groups. From the spectra of the modified and unmodified HA with carbon-13 of natural abundance it can be concluded that the applied preparative modification procedure causes only the desired structural changes in HA.

Catalysis by colloidal polymers in aqueous media

Crosslinked polymer latexes were prepared by emulsion copolymerization of either styrene or one of 14 different alkyl methacrylates and vinylbenzyl chloride and converted to quaternary ammonium ion latexes by reaction with trimethylamine or tributylamine. As catalytic colloidal media the cation exchange latexes increased the rate decarboxylation of 6-nitrobenzisoxazole-3-carboxylate up to 10 000 times and the rate of basic hydrolysis of p-nitrophenyl alkanoates up to 16 times in aqueous dispersions at room temperature. Latexes containing either 2-ethylhexyl methacrylate as the inert component of the polymer or tributylammonium ion active sites were most active. Catalytic activity for the decarboxylation did not depend on particle size when the diameter was <1 μm. Polyampholyte latexes containing 29/18 and 25/23 molar ratios of styrylmethyl(trimethyl)ammonium cations and methacrylate anions were colloidally stable in 4 M NaCl. Catalytic activity decreased with increasing concentrations of NaCl in the dispersions, and all of the latexes except the polyampholytes coagulated at>0.1 M NaCl. Dendrimers having one hydrophobic octyl group and one hydrophilic tri(ethylene glycol) methyl ether group on each tertiary amine end were prepared from commercial poly(propylene imine) dendrimers having eight and 32 primary amine end groups and were converted to quaternary ammonium dendrimers by methyl iodide. After ion-exchange for chloride, the polycationic dendrimers increased the rate of the decarboxylation by 200–500 times the rate in pure water.