Ester Oxygen Atom Research Articles

L-cysteine ethyl ester prevents and reverses acquired physical dependence on morphine in male Sprague Dawley rats.

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the co-administration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150mg/kg) for 36h and were receiving a continuous infusion of saline (20μL/h, IV) via osmotic minipumps for the same 36h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8μmol/kg/h, IV) for 36h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150mg/kg) for 48h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150mg/kg for 48h)-treated rats that began receiving an infusion of L-CYSee (20.8μmol/kg/h, IV) at 36h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of L-CYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans.

Investigation of transition metal chelates with a ligand (3-cyano-6-thiophen-2-yl[4,4′]bipyridinyl-2-yloxy)-acetic acid hydrazide as corrosion inhibitors for copper in 1.0 M HCl solution

Mn(II), Fe(III),Co(II), Ni(II) and Cu(II) complexes of the ligand named (3-Cyano-6-thiophen-2-yl[4,4′]bipyridinyl-2-yloxy)-acetic acid hydrazide (abbreviated as HL) have been synthesized. Structure assignment of such chelates have been performed by means of analytical and spectral tools which joint assured the formulation of the chelates in 1 M: 1 L ratio with non-electrolytic character for all the complexes. Fe(III) complex is 1:3 electrolyte. The spectral IR toll proved the neutral tridentate ligand nature connecting to the metal ions by the azomethine nitrogen, carbonyl and ester oxygen atoms. Octahedral structure has been concluded for all the isolated chelates as deduced from the UV-Vis spectral analysis. The investigated complexes were tested to protect or restrain the corrosion of copper in 1.0 M HCl solution at 298 K using different techniques. The outcomes being acquired illuminated that the synthesized compounds were discovered to be efficient inhibitors and their % IEs were concluded to be dependent on both concentrations and structures. The order of the % IEs of the tested compounds was: HL-Mn> HL-Fe> HL-Co ≥ HL- Ni> HL-Cu> HL. The acquired high % IEs were ascribed to the powerful adsorption of the organic molecules on the surface of copper which was agreed with Langmuir adsorption isotherm. The kinetics of corrosion inhibition by the examined compounds appeared negative-first order process. PDP results indicated that the complex HL-Mn behaves as a mixed-kind inhibitor with slight anodic seniority. The employed techniques used for the complex HL-Mn were in a good consistence with each other.

Enhanced Fluorescence by Inter/Intramolecular Hydrogen Bonding in Si-Substituted Coumarins

Introducing heteroatoms in organic fluorophores offers a unique strategy to tune their photophysical properties without dangling structural decorations. Silicon-substituted coumarins (Si-coumarins) are the analogues of coumarin with the substitution of ester oxygen atoms by silicon atoms. In Si-coumarins, significant fluorescence enhancement in protic solvents through the formation of inter/intramolecular hydrogen bonds (H-bonds) offered great potential in various aspects with many unique photophysical properties. The energies of nπ* and ππ* states in Si-coumarins are elaborately tuned by inter/intramolecular H-bonds and solvents after incorporating silicon atoms. For example, the inter/intramolecular H-bonds elevate the energy of the nπ* state in protic solvents, leading to an enlarged energy gap between the nπ* and ππ* states. Thus, fluorescence is enhanced by reducing the nonradiative transition through the nπ* state in coumarins, resulting in many unique photophysical properties. The understanding of H-bonds in Si-coumarins offers more potential strategies for the design of novel fluorophores.

Conformational and solvent effects in structural and spectroscopic properties of 2-hydroxyethyl methacrylate and acrylic acid

• 2-Hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) were investigated through MD simulations and DFT calculations. • Properties derived from simulations were compared to experimental electronic and vibrational spectra. • Different solvation models were used in theoretical spectra calculation. 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) are monomers widely used in the production of hydrogels with medium-high water content. The structural and spectroscopic properties of HEMA and AA were studied using a combination of computational strategies based on both density functional theory (DFT) calculations and molecular dynamics (MD) simulations. DFT calculations have confirmed the co-existence of two stable HEMA conformers, while solute-solvent interactions between HEMA and AA with water were characterized by the analysis of MD simulations carried out by employing four different water models and different simulation conditions. The carbonyl and hydroxyl oxygen atoms of HEMA are involved in hydrogen bonding, whereas the ester oxygen atom does not appreciably interacts with the solvent. No significant differences in solute-solvent interactions are found between the two HEMA conformers. Their spectroscopic properties were calculated and the results were compared to experimental data. Although electronic spectra do not really allow a differentiation of the conformers, IR spectra present some peculiar bands to discriminate the presence and obtain information on the ratio of the conformers in solution. To verify the influence of a solvent with higher dipole moment on chemical properties, acetonitrile has been considered as an alternative solvent.

Synthesis of salicylates from anionically activated aromatic trifluoromethyl group

An efficient approach to salicylates via a novel transformation of anionically activated aromatic trifluoromethyl group is described. Anionically activated trifluoromethyl group can react with phenols/alcohols under alkaline conditions to afford aryl/alkyl salicylates in high yields. Mechanism studies indicate that the carbonyl oxygen atom of ester is from the H2O in the solvent.

Microhydration of sorbitan monostearate (Span 60) investigated using hybrid QM/MM calculations in the gas phase

The binding interactions and structural and electronic properties involved in microhydration of Span 60•(H2O)n (n = 1–10) complexes were investigated using hybrid QM/MM calculations in the gas phase. The Span 60 head group and its hydrating water molecules were treated using the QM method, while the Span 60 tail group was treated with the MM method. For the monohydration complex, it was revealed that the hydration energy and binding force are strongly dependent on the hydration sites (O1–O6) of the Span 60 head group. The ether oxygen (O4) exhibited the highest hydration energy and the strongest hydrogen bonds. An ester oxygen atom (O2) showed a lower binding force due to its delocalized lone pair electrons. For polyhydration complexes, it was found that the average hydration energy of each polyhydration complex is close to that of the monohydrated form because of steric hindrance and electrostatic repulsions between water molecules. Interaction between the ether oxygen (O4) and water molecules is still prominent for all polyhydration complexes. The charge transfer phenomenon is noticeably altered when a few water molecules bind with a particular oxygen atom of the Span 60 head group, leading to an increase in the polarity of this group. Hydrogen bond lengths tend to decrease slightly and the conformation change of the Span 60 head group is significantly affected as the number of hydrated water molecules increases.

Superior acidic sulfate ester group based high conductive membrane for vanadium redox flow battery

Proton conductive group is essential to provide ion transport site and tune micro-phase separation in proton exchange membranes for vanadium redox flow battery (VRFB), while nearly all the fabrication methods are based on the benchmark sulfonic acid group. Herein, the sulfate ester group (-OSO3H) with superior acidity is proposed as a novel proton conductive group to achieve high proton transport at lower IECs, therefore disentangles the trade-off between vanadium crossover and conductive ion diffusion. The electron withdrawing ester oxygen atom endows sulfate ester group with 27 kJ mol−1 lower proton binding energy than the sulfonic acid group, leading to higher proton dissociation ability and better micro-phase separation. The 1,3-propanediol cyclosulfate grafted polybenzimidazole with IEC of 1.85 (OPBI-OSO3H-1.85) reaches comparable area resistance (0.19 Ω cm−2) to the sulfonic acid grafted polybenzimidazole with much higher IEC of 2.95 (OPBI-SO3H-2.95), but 19.1% decrease in vanadium permeability. The cell assembled with OPBI-OSO3H-1.85 achieves high energy efficiency of about 86.7% and low decay of discharge capacity (0.41% per cycle), superior to that of OPBI-SO3H-2.95 (0.51% per cycle) and Nafion 212 (0.71% per cycle). The sulfate ester group is proved to be chemically stable in H2SO4/vanadium environment.

A fresh-bias photoresponse of graphene field-effect transistor: An electrical tunable fast dipole moment generation

A unique extra photoresponse of graphene field-effect transistor to the first laser pulse after a switch of back-gate voltage (VBG) is reported and explored here. It is referred as fresh-bias photoresponse (FBPR). FBPR suggests a unique prompt charge transfer process triggered by laser illumination with the help of the VBG and the transferred charge holds as far as the VBG holds unchanged. The responsible charge transfer process is proposed between ester oxygen and carbonyl carbon atoms in the ester side chains of poly(methyl methacrylate) (PMMA) molecule. The proposed mechanism explains perfectly all of the features of FBPR. The charge transfer process generates an inter-molecular dipole moment of PMMA. Such dipole moment generation is much fast than that introduced by a photo-triggered isomerization reaction of photochromic molecule, which have been used in graphene based photodetectors. This mechanism is further confirmed by the test result of a control device with mechanically exfoliated graphene channel and a control device fabricated on hexagonal boron nitride substrate. The mechanism behind FBPR may provide a new way of developing phototransistors, photodetectors or photoelectronic memory devices in the future.

Cytotoxicity of N-(P-chlorophenyl)-7-hydroxycoumarin -3-yl carboxamide and Ethyl 7-hydroxycoumarin-3-yl Ester

Background: Coumarins (2H-1-benzopyran-2-one), an important class of heterocyclic compounds, and its derivatives can be found in many natural or synthetic drug molecules and possess versatile bioactivities making them important molecules for medical practitioners and medicinal chemists.
 Aims and Objective: Our study aims to evaluate cytotoxicity of new Coumarin derivatives: N-(P-chlorophenyl)-7-hydroxycoumarin-3-yl carboxamide (comp-3) and Ethyl 7-hydroxycoumarin-3-yl ester (comp-2) against four human cell lines such as human breast cancer (MCF-7), human liver cancer (HEPG-2), human colon cancer (HCT) and human prostate cancer cell (PC-3).
 Methodology: The ethyl-7-hydroxycoumarin-3-ylester (comp-2) was prepared via cyclocon-densation of 2, 4-dihydroxybenzaldhyde with diethylmalonate in the presence of piperidine under fusion followed by Amonolyses with 4-chloro-aniline in the presence of acid medium under fusion produced the N-(4-chlorophenyl)-7-hydroxycoumarin-3-yl carboxamide (comp-3).
 Result: The synthesized compounds have potent cytotoxicity against different tumor cell lines (MCF-7, HEPG-2, HCT, and PC-3).
 Discussion: The compound N-(P-chlorophenyl)-7-hydroxycoumarin-3-yl carboxamide (comp-3) is better than Ethyl 7-hydroxycoumarin-3-yl ester (comp-2) because of the nature of the halogen atom (a chlorine or a bromine atom) in the ‘meta’ position of the phenyl ring relative to the ester oxygen atom of 2-oxo-2H-1-benzopyran- 3-carboxylate led to a better anti-tumor effect than that observed in the absence of any substituent.

Biochemical Studies on Coumarin Derivatives as Antioxidant and Antitumor Agents

Background: Coumarin derivatives have attracted intense interest in recent years, because they have anti-tumor, antioxidant activities, and induce apoptosis.
 Aims and Objective: Our study aims to evaluate the antitumor and anti-oxidant activities of new Coumarin derivatives: N-(P-chlorophenyl)-7-hydroxycoumarin-3-yl carboxamide and Ethyl 7-hydroxycoumarin-3-yl ester against in vivo tumor model.
 Methodology: the toxicity for the synthesized compounds was determined. The anticancer and anti-oxidant activities were studied by evaluation the viability of tumor cells, life span prolongation, and estimation of antioxidants.
 Results: Our compounds exhibited significant anti-oxidant activity towards Ehrlich ascites carcinoma (EAC) cells by reduction the MDA and NO concentration (p<0.001) compared to the positive control group. Whereas significantly increase in the G. peroxidase activity (p<0.001) in treated groups compared to the positive control group. Anticancer agent kills tumors by induction of apoptosis that showing significantly increases in Caspase-3 and Bax activity compared to positive control group.
 Discussion: The compound N-(P-chlorophenyl)-7-hydroxycoumarin-3-yl carboxamide is better than Ethyl 7-hydroxycoumarin-3-yl ester compound because of the nature of the halogen atom (a chlorine or a bromine atom) in the ‘meta’ position of the phenyl ring relative to the ester oxygen atom of 2-oxo-2H-1-benzopyran- 3-carboxylate led to a better anti-tumor effect than that observed in the absence of any substituent.

Local structure and hydrogen bonding in liquid γ-butyrolactone and propylene carbonate: A molecular dynamics simulation

In this work we report a new potential model for classical molecular dynamics (MD) simulation of two dipolar aprotic solvents – propylene carbonate (PC) and γ-butyrolactone (GBL). Parameters for intramolecular interactions as well as the partial atomic charges were derived from quantum chemical calculations, while the OPLS/AA force field Lennard-Jones intermolecular parameters were adjusted to reproduce the experimental thermodynamic and the transport properties of these solvents in the wide temperature range. The comparison of new potential models with existing models for PC and GBL is given. Using the proposed models, the local structure of these solvents was studied in detail, paying special attention to packing ability, dipole-dipole orientation and hydrogen-bonding (H-bonding) interactions. Based on the results of MD simulations and QTAIM analysis, it was shown that H-bonds involving carbonyl oxygen atoms in PC and GBL are rather weak, while no H-bonds are formed with ester oxygen atoms. According to the present results, the mutual molecular orientation in PC and GBL varies with the distance, being above/below plane-parallel configuration for closest neighbors, and in-plane T-shaped configurations for farther neighbors. The nearest neighbors approach coupled with angular distribution functions was applied for the estimation of the Kirkwood factor in the framework of the Onsager-Kirkwood-Fröhlich theory. Our results shows that in order to reproduce the corresponding experimental values the Kirkwood factor it is necessary to take in account the mutual orientation of ~8–9 neighboring molecules for GBL and ~5–6 molecules for PC.

Determination of the Structure of Alkyl Radicals in a Series of Highly Toxic Organophosphorus Compounds Using Mass Spectrometry Databases and Library Search

We propose an approach to the identification of alkyl radicals attached to the ester oxygen atom in a series of highly toxic organophosphorus compounds, based on the revealed regularities in the formation of mass spectra of monofunctional RX compounds (R is alkyl radical and X is functional group). The method includes the extraction of the hydrocarbon subspectrum from the mass spectrum of the analyte and its comparison with the hydrocarbon subspectra of the known monofunctional compounds. Alkyl radicals are identified using simple metrics that characterize the coincidence of hydrocarbon subspectra. The results of the identification of alkyl (cycloalkyl) radicals in a series of O-alkyl (cycloalkyl) alkylphosphonofluoridates, and O-alkyl (cycloalkyl) N,N-dialkylphosphoramidocyanidates show that ≥95% of the structures of the radicals of these compounds are within 10 positions of the search result list.

A molecular dynamics simulation of the structure of sodium lauryl ether sulfate and poly(vinyl alcohol) at the air/water interface

The influence of a poly(vinyl alcohol) (PVA) molecule on the air/water interfacial structure of adsorbed sodium lauryl ether sulfate with one polyethylene oxide group (SLE1S) was investigated using molecular dynamics simulations. Increasing SLE1S surface density increases the interface thickness and forces both SLE1S and PVA molecules to migrate towards the air (actually vacuum) to different degrees. While most surfactants, when dilute, align parallel with the interface, increasing surfactant surface density forces tail groups gradually to align more perpendicularly to the interface. The three types of oxygen atoms in the SLE1S head group, i.e. the ionic, ester and ether oxygen atoms, form three distinct hydration shells, with PVA monomers appearing both within these shells and between the second and third shell due to its own hydrogen bonding with water and excluded volume of surfactant and water. The ionic oxygen atoms form more hydrogen bonds with water molecules and PVA than do the ester and ether oxygen atoms. The addition of PVA decreases slightly the number of hydrogen bonds between the surfactant oxygen atoms and the water molecules, as PVA chains form new hydrogen bonds with both of them. With increasing surfactant concentration, the PVA is pushed away from the bulk water, decreasing the number of the hydrogen bonds between it and water. These results are relevant to the use of polymers to aid surfactant in aqueous foaming applications.

Synthesis of the labile rhenium(I) complexes fac-Re(CO)3(L)[κ2-O,O-FcC(O)CHC(O)Me] (where Fc = ferrocenyl; L = THF, H2O, alkyne) and alkyne addition to the diketonate ligand

Refluxing equimolar amounts of 1-ferrocenyl-1,3-butanedione (Fcacac) with BrRe(CO)5 in THF yielded the labile solvent complex fac-Re(CO)3 (THF)[κ2-O,O-FcC(O)CHC(O)Me] (1) in 80% isolated yield. 1 may also be prepared in quantitative yield using fac-BrRe(THF)2(CO)3 as the starting rhenium complex. The THF molecule in 1 is replaced by H2O during chromatographic purification to furnish the corresponding aqua complex fac-Re(CO)3(H2O)[κ2-O,O-FcC(O)CHC(O)Me] (2) while the reaction of 1 with PPh3 gives fac-Re(CO)3(PPh3)[κ2-O,O-FcC(O)CHC(O)Me] (3). Treatment of 1 with the terminal alkynes phenylacetylene and methyl propiolate proceeds rapidly at room temperature to give the π intermediates fac-Re(CO)3 (alkyne)[κ2-O,O-FcC(O)CHC(O)Me] [4 (PhC≡CH); 6 (MeO2CCCH)] that are not stable and undergo a 1,4-addition with regiospecific alkyne attack at the γ-methine site of the Fcacac moiety to afford fac-Re(CO)3 [κ3-C,O,O-FcC(O)CH(E-PhC = CH)C(O)Me] (5) and fac-Re(CO)3 [κ3-C,O,O-FcC(O)CH(Z-HC=CCO2Me)C(O)Me] (7). The solid-state structure for 5 and 7 was established by X-ray crystallography, and the computed mechanisms that account for the formation of these two products from 1 and alkyne are presented. 1 reacts with the internal alkyne dimethyl acetylenedicarboxylate (DMAD) to furnish the novel dimeric compound [fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)}]2 (9). The structure of 9 confirms the linking of the monomeric fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)} fragments through the intermolecular coordination of the ester oxygen atom associated with the α-carbomethoxy moiety of the E-metalated alkene; the latter moiety is traced to the initial DMAD insertion into the 6-membered metallocyclic ring in the π precursor fac-Re(CO)3 (MeO2CCCCO2Me)[κ2-O,O-FcC(O)CHC(O)Me].

Regioselective Neighboring-Group-Participated 2,4-Dibromohydration of Conjugated Enynes: Synthesis of 2-(2,4-Dibromobut-2-enoyl)benzoate and Its Applications.

A regioselective 2,4-dibromohydration of conjugated enynes is reported for the synthesis of 2-(2,4-dibromobut-2-enoyl)benzoate. In the presence of tetra-n-butylammonium bromide and H2O the transformation proceeds smoothly with good reaction efficiency and a broad reaction scope. Mechanism studies indicate that the neighboring ester group participates in the 2,4-dibromohydration, and the oxygen atom of ester is transferred into the C-C triple bond to form the keto carbonyl group in the product. 2-(2,4-Dibromobut-2-enoyl)benzoate is recognized as an important synthon toward phthalazin-1(2H)-one and the natural product Shihunine.

Influence of Small Fluorophilic and Lipophilic Organic Molecules on Dipalmitoylphosphatidylcholine Bilayers.

In this study, we investigate the effect of a series of additive molecules with different types of philicities on the structure and dynamics of dipalmitoylphosphatidylcholine (DPPC) bilayers. To this aim, we performed extensive force field molecular dynamics simulations of the systems, using our recently developed perfluoroalkane force field. We found that addition of perfluoro-n-decane and fluorotelomer alcohol at 323 K leads to a phase transition of the membrane from liquid crystalline to the gel phase, whereas the addition of n-decane and partially fluorinated n-decane leaves the liquid crystalline phase intact. The systems in the gel phase show a significantly reduced diffusivity for both DPPC and additive molecules. The addition of nonfluorinated and partially fluorinated n-decane even leads to an increased DPPC diffusivity. While nonfluorinated n-decane and partially fluorinated n-decane are found mainly in the middle of the bilayer, perfluoro-n-decane penetrates significantly deeper into the membrane leaflet. Fluorotelomer alcohol is found almost exclusively inside the leaflet, with its hydroxyl groups forming a strong hydrogen bond network to the ester oxygen atoms in the head group of DPPC. A slight increase in temperature by only 10 K is already sufficient to dynamically overcome this hydrogen bond network, such that no phase transition occurs in that case.

Topological control of supramolecular crystal structures of phenylene bis-monothiooxamate derivatives and in vitro anticancer activity

This paper describes the synthesis, physical characterization, X-ray crystal structures and antitumoral activity against human carcionogenic cells of three new diethyl ester acid derivatives of phenylene bis-monothiooxamate compounds, namely Et2H2opbta (1), Et2H2mpbta (2) and Et2H2ppbta (3) [opbta = N,N′-1,2-phenylenebis(2-thiooxamate), mbpta = N,N′-1,3-phenylenebis(2-thiooxamate) and ppbta = N,N′-1,4-phenylenebis(2-thiooxamate)]. Compounds 1–3 were obtained under mild conditions by reaction of the corresponding N,N′-phenylenebis(oxamate) analogues and Lawesson's reagent resulting in the formation of CS bonds at the carbonyl amide functions. Crystal structures of 1–3 consist of 1D supramolecular assemblies of centrosymmetric H2Et2ppbta (3) or noncentrosymmetric chiral H2Et2opbta (1) and H2Et2mpbta (2) molecules with opposite helical chirality (M and P enantiomers) resulting from intermolecular NH⋯O (1 and 3) or NH⋯S (2) hydrogen bonds between the amide hydrogen atoms and the carbonyl ester oxygen or thionyl amide sulfur atoms from the thiooxamate moieties respectively, together with weak S⋯S bonds between the thionyl amide sulfur atoms (1). The cytotoxicity of H2Et2xpbta [x = o (1), m (2) and p (3)] against chronic myelogenous leukemia cells was evaluated and the bioactivity follows the order 1 ≫ 2 > 3, compound 1 being six and ten times more active than 2 and 3, respectively.

Pairwise Packing of Anthracene Fluorophore: Hydrogen-Bonding-Assisted Dimer Emission in Solid State

Anthracene derivatives possessing a carbamate group and an ester group at their 9- and 10-positions, respectively, were prepared to furnish pairwise packing of anthracene fluorophores in their crystal structures. They were nonluminescent in ethanol solution and showed AIE (aggregation-induced emission) in aqueous ethanol solution and in solid state. Crystal structure analysis of them showed that the H-bonding networks involved in their crystal structures could be classified into four patterns, H-bonding between the carbamate and the ester carbonyl (motif A), H-bonding between the carbamate and the ester oxygen atom (motif B), H-bonded cyclic dimer of carbamate moieties (motif C), and H-bonded chain among carbamate moieties (motif D). Compounds with pairwisely packed anthracene fluorophores showed dimer emission with the longer fluorescence wavelength than others without the pair formation. Fluorescence maximum wavelengths and lifetimes become longer proportional to the degree of overlapping of two facing anthracene π-planes.

ChemInform Abstract: Activation of Alkynes with B(C6F5)3 — Boron Allylation Reagents Derived from Propargyl Esters.

Novel allyl boron compounds are readily synthesized via rearrangement reactions between Lewis acidic B(C6F5)3 and propargyl esters. These reactions proceed through an initial cyclization followed by ring-opening and concurrent C6F5-group migration. In the absence of disubstitution adjacent to the ester oxygen atom, an allyl boron migration rearrangement leads to formal 1,3-carboboration products. These allyl boron compounds act as allylation reagents with aldehydes introducing both a C3-allyl fragment and a C6F5-unit as a single anti-diastereomer. In these reactions, B(C6F5)3 activates the alkynes, prompting the rearrangement processes and enabling installations of C6F5 and R-groups.

Remarkably regioselective deacylation of cellulose esters using tetraalkylammonium salts of the strongly basic hydroxide ion

Tetraalkylammonium hydroxides have been found to mediate regioselective deacylation of cellulose esters. This deacylation surprisingly shows substantial selectivity for the removal of the acyl groups at O-2/3, affording cellulose-6-O-esters by a simple, efficient one-step process. The mechanism for this deacylation was investigated by studying the effect of tetraalkylammonium cation size upon ester deacylation selectivity. We hypothesize that coordination of the tetraalkylammonium cation by the ester oxygen atoms of the vicinal 2,3-acetate groups may drive the unexpected regioselectivity at the secondary alcohol esters. Broad scope with respect to ester type was demonstrated; regioselective O-2,3 deacylation was observed with cellulose acetate, propionate, butyrate, hexanoate and benzoate triesters. The scope of this deacylation of cellulose acetates has been investigated to understand how to carry it out most efficiently. Reaction with TBAOH in pyridine was the most effective process, providing the highest selectivity.