Nonhydrolytic Conditions Research Articles

Cleavage of Carboxylic Esters by Aluminum and Iodine.

A one-pot procedure for deprotecting carboxylic esters under nonhydrolytic conditions is described. Typical alkyl carboxylates are readily deblocked to the carboxylic acids by the action of aluminum powder and iodine in anhydrous acetonitrile. Cleavage of lactones affords the corresponding ω-iodoalkylcarboxylic acids. Aryl acetylates undergo deacetylation with the participation of the neighboring group. This method enables the selective cleavage of alkyl carboxylic esters in the presence of aryl esters.

Tin stearate organometallic precursor prepared SnO2 quantum dots nanopowder for aqueous- and non-aqueous medium photocatalytic hydrogen gas evolution

Current study reports a rapid one-pot non-hydrolytic condition in the synthesis of SnO2 QDs nanopowder using tin (II) stearate (Sn(St)2) as environmentally-benign organometallic precursor, which is an unprecedentedly employed-compound in preceding SnO2 nanopowder productions. The as-synthesized SnO2 QDs that are hydrophobic can be easily transferred from organic solvent to aqueous solution through a robust ligand exchange method. The stearate-capping ligands on the surface of QDs can be replaced by beta-cyclodextrin (β-CD) and eventually render the QDs highly water soluble, which ultimately make it exhibit bi-functionality for different liquid medium applications. Structural characterizations reveal that the bi-functional QDs are indeed well-matched with the standard rutile SnO2 cassiterite phase without the presence of any impurities. The QDs can be interchangeably used as photocatalyst for both aqueous and non-aqueous phase, where it shows significant enhancement of hydrogen gas production as compared to that of commercial SnO2 nanopowder.

Synthesis, Structural Features, Cytotoxicity, and Magnetic Properties of Colloidal Ferrite Spinel Co1–xNixFe2O4(0.1 ≤ x ≤ 0.9) Nanoparticles

AbstractColloidal ferrite spinel nanoparticles (CoxNi1–xFe2O4) were prepared by a microwave‐stimulated Bradley technique under nonhydrolytic conditions. The effect of Ni2+doping on the structural properties was studied by powder XRD. The particle size, hydrodynamic size, and morphology were evaluated by transmission electron microscopy (TEM) and dynamic light scattering (DLS), which showed mean crystallite sizes of ca. 10 and 60 nm for powder and colloidal suspensions of CoxNi1–xFe2O4, respectively. The cytotoxicity of the nanoparticles was tested against murine macrophages J774.E, osteosarcoma D17 cells, and human red blood cells (RBCs). The adsorption of bovine serum albumin (BSA) was studied, and the BSA showed a high affinity for the surface of the nanoparticles. The CoxNi1–xFe2O4nanoparticles in colloidal suspension showed dose‐dependent cytotoxicity against all of the studied cell lines, and less harmful effects were observed against RBCs at concentrations of up to 0.1 mg/mL. The cytotoxicity towards the D17 and J774.E cells suggests that internalization by the living cells seems to be the key step to elicit the toxic response. Thus, the cytotoxicity of the particles under investigation seems to be cell‐type‐dependent and not uniform. The CoxNi1–xFe2O4colloids exhibited superparamagnetic behavior with blocking temperatures (TB) below 300 K. The magnetic characteristics are well preserved in colloidal form and are similar to those of the powdered ferrites.

Nonhydrolytic Synthesis of Silanols by the Hydrogenolysis of Benzyloxysilanes

Abstract The hydrogenolysis of benzyloxysilanes was smoothly catalyzed by Pd/C in THF to give corresponding silanols under nonhydrolytic conditions. The reaction proved to be applicable to various benzyloxysilanes giving silanemonools, diol, and triol.

Conformational changes in the catalytically inactive nucleotide-binding site of CFTR

A central step in the gating of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is the association of its two cytosolic nucleotide-binding domains (NBDs) into a head-to-tail dimer, with two nucleotides bound at the interface. Channel opening and closing, respectively, are coupled to formation and disruption of this tight NBD dimer. CFTR is an asymmetric adenosine triphosphate (ATP)-binding cassette protein in which the two interfacial-binding sites (composite sites 1 and 2) are functionally different. During gating, the canonical, catalytically active nucleotide-binding site (site 2) cycles between dimerized prehydrolytic (state O1), dimerized post-hydrolytic (state O2), and dissociated (state C) forms in a preferential C→O1→O2→C sequence. In contrast, the catalytically inactive nucleotide-binding site (site 1) is believed to remain associated, ATP-bound, for several gating cycles. Here, we have examined the possibility of conformational changes in site 1 during gating, by studying gating effects of perturbations in site 1.Previous work showed that channel closure is slowed, both under hydrolytic and nonhydrolytic conditions, by occupancy of site 1 by N6-(2-phenylethyl)-ATP (P-ATP) as well as by the site-1 mutation H1348A (NBD2 signature sequence). Here, we found that P-ATP prolongs wild-type (WT) CFTR burst durations by selectively slowing (>2×) transition O1→O2 and decreases the nonhydrolytic closing rate (transition O1→C) of CFTR mutants K1250A (∼4×) and E1371S (∼3×). Mutation H1348A also slowed (∼3×) the O1→O2 transition in the WT background and decreased the nonhydrolytic closing rate of both K1250A (∼3×) and E1371S (∼3×) background mutants. Neither P-ATP nor the H1348A mutation affected the 1:1 stoichiometry between ATP occlusion and channel burst events characteristic to WT CFTR gating in ATP. The marked effect that different structural perturbations at site 1 have on both steps O1→C and O1→O2 suggests that the overall conformational changes that CFTR undergoes upon opening and coincident with hydrolysis at the active site 2 include significant structural rearrangement at site 1.

Conformational Changes in the Catalytically Inactive Nucleotide Binding Site of CFTR

A central step in the gating of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is the association of its two cytosolic nucleotide-binding domains (NBDs) into a head-to-tail dimer, with two nucleotides bound at the interface. Channel opening and closing, respectively, are coupled to formation and disruption of this tight NBD dimer. CFTR is an asymmetric adenosine triphosphate (ATP)-binding cassette protein in which the two interfacial-binding sites (composite sites 1 and 2) are functionally different. During gating, the canonical, catalytically active nucleotide-binding site (site 2) cycles between dimerized prehydrolytic (state O1), dimerized post-hydrolytic (state O2), and dissociated (state C) forms in a preferential C-->O1-->O2-->C sequence. In contrast, the catalytically inactive nucleotide-binding site (site 1) is believed to remain associated, ATP-bound, for several gating cycles. Here, we have examined the possibility of conformational changes in site 1 during gating, by studying gating effects of perturbations in site 1.Previous work showed that channel closure is slowed, both under hydrolytic and nonhydrolytic conditions, by occupancy of site 1 by N6-(2-phenylethyl)-ATP (P-ATP) as well as by the site-1 mutation H1348A (NBD2 signature sequence). Here, we found that P-ATP prolongs wild-type (WT) CFTR burst durations by selectively slowing (>2x) transition O1-->O2 and decreases the nonhydrolytic closing rate (transition O1-->C) of CFTR mutants K1250A ( approximately 4x) and E1371S ( approximately 3x). Mutation H1348A also slowed ( approximately 3x) the O1-->O2 transition in the WT background and decreased the nonhydrolytic closing rate of both K1250A ( approximately 3x) and E1371S ( approximately 3x) background mutants. Neither P-ATP nor the H1348A mutation affected the 1:1 stoichiometry between ATP occlusion and channel burst events characteristic to WT CFTR gating in ATP. The marked effect that different structural perturbations at site 1 have on both steps O1-->C and O1-->O2 suggests that the overall conformational changes that CFTR undergoes upon opening and coincident with hydrolysis at the active site 2 include significant structural rearrangement at site 1.

Two Neonatal Diabetes Mutations on Transmembrane Helix 15 of SUR1 Increase Affinity for ATP and ADP at Nucleotide Binding Domain 2

K(ATP) channels, (SUR1/Kir6.2)(4) (sulfonylurea receptor type 1/potassium inward rectifier type 6.2) respond to the metabolic state of pancreatic β-cells, modulating membrane potential and insulin exocytosis. Mutations in both subunits cause neonatal diabetes by overactivating the pore. Hyperactive channels fail to close appropriately with increased glucose metabolism; thus, β-cell hyperpolarization limits insulin release. K(ATP) channels are inhibited by ATP binding to the Kir6.2 pore and stimulated, via an uncertain mechanism, by magnesium nucleotides at SUR1. Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. GBC binds with high affinity to aporeceptors, presumably in the inward facing ATP-binding cassette configuration; MgATP reduces binding affinity via a shift to the outward facing conformation. To determine nucleotide affinities under equilibrium, non-hydrolytic conditions, Mg(2+) was eliminated. A four-state equilibrium model describes the allosteric linkage. The K(D) for ATP(4-) is ~1 versus 12 mM, Q1178R versus wild type, respectively. The linkage constant is ~10, implying that outward facing conformations bind GBC with a lower affinity, 9-10 nM for Q1178R. Thus, nucleotides cannot completely inhibit GBC binding. Binding of channel openers is reported to require ATP hydrolysis, but diazoxide, a SUR1-selective agonist, concentration-dependently augments ATP(4-) action. An eight-state model describes linkage between diazoxide and ATP(4-) binding; diazoxide markedly increases the affinity of Q1178R for ATP(4-) and ATP(4-) augments diazoxide binding. NBD2, but not NBD1, has a higher affinity for ATP (and ADP) in mutant versus wild type (with or without Mg(2+)). Thus, the mutants spend more time in nucleotide-bound conformations, with reduced affinity for GBC, that activate the pore.

Ti8O8(OOCR)16, a New Family of Titanium–Oxo Clusters: Potential NBUs for Reticular Chemistry

AbstractThe reactions of titanium alkoxides with a large excess of different carboxylic acids under nonhydrolytic conditions leads to the reproducible formation of well‐defined nano‐building units (NBUs) with the formula [Ti8O8(OOCR)16] [R = C6H5, C(CH3)3, CH3]. The structures of these titanium–oxo–carboxylate clusters have been determined by crossingdifferent characterization techniques and methodologies (single‐crystal X‐ray diffraction, 13C and 1H NMR spectroscopy, and FTIR spectroscopy). These NBUs are obtained in high yields and, since all the alkoxo ligands have been removed by using solvothermal‐synthesis conditions, they present better stability upon hydrolysis than the often reported alkoxo–carboxylate–titanium–oxo clusters [TinO2n–x/2–y/2(OR′)x(OOCR)y] (n ≥ 2; x ≥ 1; y ≥ 1). In addition, the solubility and transferability of these clusters in common solvents can be tuned by selecting the nature of the organic ligand. Moreover, we also report for the first time, a robust post‐modification of the carboxylate ligands by transesterification reactions on the titanium–oxo clusters. These reactions keep the integrity of the octameric titanium–oxo core intact, while completely exchanging the organic shell of the cluster. This family of [Ti8O8(OOCR)16] clusters, which present 16 points of extension, a symmetric shape, and the ability to be post‐modified with conservation of the core structure, can therefore be considered as interesting NBUs to form new metal–organic frameworks.

Sulfonation of the surface of cordierite monoliths through a novel multi-step wet chemical process

A novel multi-step wet chemical process was developed to enhance the surface chemistry of cordierite monoliths by the chemical incorporation of sulfonic groups via an alkoxide type molecular precursor of silica previously bonded to the surface. The wet chemical process involved three steps: activation of the surface, bonding to the surface of a hybrid molecular precursor of silicon having an aromatic ring moiety, and chemical modification by sulfonation of the organic moiety in the hybrid precursor. The activation step was carried out to improve the surface area and create a rich surface chemistry based on hydroxyl groups capable of performing heterocondensation with the hybrid precursor. Two acid bath treatments were used to bring about the activation of the surface, being the first one based on hydrochloric acid and the second one on a mixture sulfuric acid–hydrogen peroxide. The reaction between the hydroxyl groups on the surface and the molecular precursor of silicon was done under non-hydrolytic conditions using toluene as a solvent. A mixture of chlorosulfonic acid and concentrated sulfuric acid was used to do the sulfonation. BET surface area, BJH nitrogen pore size distribution, diffuse reflectance Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and differential scanning calorimetry were the techniques used to characterize the solids. All of these characterizations showed a successful modification of the surface. Ionic exchange capacities of 0.062 and 0.076 meq/g and BET surface areas of 66 and 102 m 2/g, respectively, were obtained for materials prepared following two different procedures for the activation. The enhanced materials showed a thermal degradation beginning at 450 °C.

Heterogeneous Seeded Growth: Synthesis and Characterization of Bifunctional Fe3O4/ZnO Core/Shell Nanocrystals

In the present study, Fe3O4/ZnO core/shell nanocrystals (NCs) are synthesized via seed-meditated growth approach in nonhydrolytic condition. The controlling process of thermal pyrolysis of zinc acetate (ZnAc) renders a condition to overgrow ZnO layer on the surface of Fe3O4 NCs (seeds). The transmission electron microscope (TEM) micrograph shows that Fe3O4/ZnO NCs are spherical in shape, highly monodispersed, and exhibiting responding shell thickness by varying the mole ratio of seed to shell precursor. The X-ray powder diffraction patterns (XRD) for Fe3O4/ZnO NCs reveal the coexistence of both Fe3O4 and ZnO crystal structures, which the patterns can be well indexed with the standard powder diffraction patterns of both materials. The NCs exhibit superparamagnetism corresponding to an external magnet field provided by vibrating sample magnetometer (VSM) and show red-shift phenomenon under UV excitation at room temperature. The NCs are magnetically separable upon application of 0.6 T magnet, which shows tha...

DNA Conformational Dynamics in Mismatch Recognition

DNA mismatch recognition is done by the homodimer MutS in prokaryotes and by its homologues: heterodimers Msh2-Msh3 and Msh2-Msh6 in eukaryotes. Msh2-Msh6 binds preferentially to single insertion/deletions. Msh2-Msh3 has been shown to bind to DNA hairpins. It has been suggested that the conformational dynamics of the DNA substrate (bending and unbending) plays a fundamental role in the recognition process. Mismatch recognition allows identifying a single mismatched DNA pair among thousands of matched basepairs. The process is ATP dependent and different models for DNA discrimination have been proposed based in biochemical evidence as well as AFM studies. In this work we study the conformational dynamics of several DNA substrates and its complexes with the human MutS homologs. The DNA substrates were labeled with fluorescent dyes that constitute a fluorescence resonant energy transfer (FRET) pair. Experiments at the single molecule level allow us to follow the conformational dynamics of the substrates by determining the substrate's end to end distance. We were able to determine the binding and dissociation rates of the proteins from the substrates as well as the conformational state of the substrates under different conditions, including studies with ATP and ADP under both hydrolytic and non-hydrolytic conditions. In particular we discuss the role of the substrate's intrinsic dynamics for binding of hMsh2-hMsh3 to DNA hairpins and DNA 3-way junctions.

New Syntheses and Ring Expansion Reactions of Cyclobutenimines

Two routes are reported for the synthesis of iminocyclobutenones having N-(het)aryl substitution: an addition/substitution sequence starting with cyclobutenediones and an aza-Wittig method. A new synthetic route to N-alkyl derivatives is also presented. This involves O-alkylation of 3-alkylamino-1,2-cyclobutenediones using Meerwein’s reagent and subsequent deprotonation under non-hydrolytic conditions. Lithium organyls were found to add to the remaining carbonyl group. The resulting tertiary alcohols undergo ring enlargement on heating in xylene to give 4-aminophenols, 4-amino-1-naphthols, or cyclopenta-annulated quinolines from 4-vinyl, 4-aryl, and 4-alkynyl derivatives, respectively.

Modulation of MutS ATP-dependent Functional Activities by DNA containing a Cisplatin Compound Lesion (Base Damage and Mismatch)

DNA damage-dependent signaling by the DNA mismatch repair (MMR) system is thought to mediate cytotoxicity of the anti-tumor drug cisplatin through molecular mechanisms that could differ from those required for normal mismatch repair. The present study investigated whether ATP-dependent biochemical properties of Escherichia coli MutS protein differ when the protein interacts with a DNA oligonucleotide containing a GT mismatch versus a unique site specifically placed cisplatin compound lesion, a cisplatin 1,2-d(GpG) intrastrand cross-link with a mispaired thymine opposite the 3′ platinated guanine. MutS exhibited substantial affinity for this compound lesion in hydrolytic and in non-hydrolytic conditions of ATP, contrasting with the normal nucleotide inhibition effect of mispair binding. The cisplatin compound lesion was also shown to stimulate poorly MutS ATPase activity to approach the hydrolysis rate induced by nonspecific DNA. Moreover, MutS undergoes distinct conformation changes in the presence of the compound lesion and ATP under hydrolytic conditions as shown by limited proteolysis. In the absence of MutS, the cisplatin compound lesion was shown to induce a 39° rigid bending of the DNA double helix contrasting with an unbent state for DNA containing a GT mispair. Furthermore, an unbent DNA substrate containing a monofunctional adduct mimicking a cisplatin residue failed to form a persistent nucleoprotein complex with MutS in the presence of adenine nucleotide. We propose that DNA bending could play a role in MutS biochemical modulations induced by a compound lesion and that cisplatin DNA damage signaling by the MMR system could be modulated in a direct mode.

Silica Structures Templated on Fibers of Tetraalkylphosphonium Salt Gelators in Organogels

Phosphonium cations (18(n)RP(+)) consisting of three or four n-octadecyl chains and R = PhCH(2) or C(m)H(2)(m+1) (m = 1-5 or 12) when n = 3 and with iodide, bromide, chloride, fluoride, or perchlorate anions are used to gelate and polymerize solutions of 2-10 wt % tetraethyl orthosilicate in ethanol, benzene, tetrahydrofuran, and dimethyl sulfoxide using acid or base catalysis and under hydrolytic or nonhydrolytic conditions. These are the simplest low-molecular-mass organic gelator structures of which we are aware that have been able to template silica. The silica objects that are obtained after the hydrolytic sol-gel process include porous, spherulitic, and tubular objects in the size range of several micrometers to tens of nanometers. Their specific shapes and sizes depend on the specific conditions of the hydrolytic sol-gel process, including the nature of the catalyst. The electrostatic interaction between silicate intermediates and gelator strands is the driving force for templating. The template effect is strongly influenced by several factors, including (1) the competition between silicate/solvent and silicate/template interactions, (2) the period of the sol-gel process, (3) the hardness of the anion of the gelator salt, (4) the surface tension of the solvent, (5) and the sequence of drying and template removal processes. The nature of the R group influences the stability of the molecular gels but appears to have little effect on the silica morph obtained. In addition, it is shown in one case, where a direct comparison is possible, that the fibers of one of our phosphonium salts are a much more efficient template for silica than those of the corresponding ammonium salt (with its "harder" cationic center). The specific nature of the objects and the conditions under which they can be formed are discussed.

Modulator-Induced Interference in Functional Cross Talk between the Substrate and the ATP Sites of Human P-glycoprotein

The human P-glycoprotein (Pgp, ABCB1) is an ATP-dependent efflux pump for structurally unrelated hydrophobic compounds, conferring simultaneous resistance to and restricting bioavailability of several anticancer and antimicrobial agents. Drug transport by Pgp requires a coordinated communication between its substrate binding/translocating pathway (substrate site) and the nucleotide binding domains (NBDs or ATP sites). In this study, we demonstrate that certain thioxanthene-based Pgp modulators, such as cis-(Z)-flupentixol and its closely related analogues, effectively disrupt molecular cross talk between the substrate, and the ATP, sites without affecting the basic functional aspects of the two domains, such as substrate recognition, binding, and hydrolysis of ATP and dissociation of ADP following ATP hydrolysis. The allosteric modulator cis-(Z)-flupentixol has no effect on [alpha-(32)P]-8-azido-ATP binding to Pgp under nonhydrolytic conditions or on the K(m) for ATP during ATP hydrolysis. Both hydrolysis of ATP and vanadate-induced [alpha-(32)P]-8-azido-ADP trapping (following [alpha-(32)P]-8-azido-ATP breakdown) by Pgp are stimulated by the modulator. However, the ability of Pgp substrates (such as prazosin) to stimulate ATP hydrolysis and facilitate vanadate-induced trapping of [alpha-(32)P]-8-azido-ADP is substantially affected in the presence of cis-(Z)-flupentixol. Substrate recognition by Pgp as determined by [(125)I]iodoarylazidoprazosin ([(125)I]IAAP) binding both in the presence and in the absence of ATP is facilitated by the modulator, whereas substrate dissociation in response to vanadate trapping is considerably affected in its presence. In the Pgp F983A mutant, which is impaired in modulation by cis-(Z)-flupentixol, the modulator has a minimal effect on substrate-stimulated ATP hydrolysis as well as on substrate dissociation coupled to vanadate trapping. Finally, cis-(Z)-flupentixol has no effect on dissociation of [alpha-(32)P]-8-azido-ADP (or ADP) from vanadate-trapped Pgp, which is essential for subsequent rounds of ATP hydrolysis. Taken together, our results demonstrate a distinct mechanism of Pgp modulation that involves allosteric disruption of molecular cross talk between the substrate, and the ATP, sites without any direct interference with their individual functions.

ChemInform Abstract: Diphenyl Disulfide and Sodium in NMP as an Efficient Protocol for in situ Generation of Thiophenolate Anion: Selective Deprotection of Aryl Alkyl Ethers and Alkyl/Aryl Esters under Nonhydrolytic Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions.

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.

Epoxy–silica polymers as restoration materials

The epoxy monomer 3-glycidoxypropyltrimethoxysilane reacts, under non-hydrolytic conditions, with the primary amine (3-aminopropyl)triethoxysilane in 2:1 ( 1), 5:1 ( 2) and 10:1 ( 3) molar ratios leading to epoxy–silica materials which were characterized by TGA, DSC, Raman, and NMR investigations. The epoxy ring opening and the hydrolysis reactions of the Si(OR) 3 groups were examined by means of 13C NMR before gelation occurs. The identification of the different types of silicate substructures present in the solids 1, 2 and 3 was accomplished by 29Si CP-MAS NMR spectroscopy which also provides a quantitative measure of the degree of condensation through the relative abundance of T 0 [RSi(OR) 3], T 1 [RSi(OR) 2OSi], T 2 [RSi(OR)(OSi) 2] and T 3 [RSi(OSi) 3] silicon nuclei. The combined results of the Raman and 29Si CP-MAS investigations clearly show that all the mixtures, especially the higher ratio ones, are characterized by a high degree of cross-linking; in addition, for 2 and 3, residual epoxy fragments are still present in the solid structure. The absence of residual enthalpy curing peaks in the calorimetric analysis indicates that the volatiles are simply released from all the samples. The thermogravimetric analysis shows that, among all the mixtures, 1 is featured by different structural properties which cause a higher degradation temperature and a longer decomposition time. To evaluate the effect of different experimental conditions on the properties of the final products, the reactions were also performed in the presence of small amounts of KOH and of a stoichiometric amount of water to effect hydrolysis of Si(OR) 3 groups.

A mild and chemoselective method for deprotection of aryl acetates and benzoates under non-hydrolytic condition

Chemoselective deprotection of aryl acetates and benzoates can be achieved under non-hydrolytic condition by treatment with K 2CO 3 in N-methyl-2-pyrrolidone (NMP) at 100°C. Selective cleavage of aryl acetates and benzoates take place in the presence of alkyl carboxylates during intramolecular competitions.

Regioselective Opening of Epoxides Catalyzed by Sn (IV). A New Method for the Synthesis of Halohydrins?

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessAbstract Regioselective Opening of Epoxides Catalyzed by Sn (IV). A New Method for the Synthesis of Halohydrins? by Claudio J. Salomon Facultad de Cs. Bioquímicas y Farmacéuticas. IQUIOS-CONICET, Universidad Nacional de Rosario. Suipacha 531, 2000 Rosario, Argentina Molecules 2000, 5(3), 468-469; https://doi.org/10.3390/50300468 Published: 22 March 2000 Download Download PDF Download PDF with Cover Download XML Download Epub Browse Figure Versions Notes Abstract: The regioselective opening of epoxides with organotin oxides 1 and 2, in presence of halogenated alcohols was developed, yielding the halohydrin derivatives. IntroductionEpoxides are among the most versatile intermediates in organic chemistry due to the particular polarity and strength of their three member ring. Those characteristics make them in a very suitable substrate to the attack or many nucleophilic and electrophilic reagents [1].The regioselective opening of oxiranes has been the subject of interest for many years, since these heterocyclics are frequently used as starting material for the preparation of natural products and biological active compounds [2].Many different organotin reagents have been employed to effect the regio- and stereoselective cleavage of oxiranes in the presence of nucleophiles affording 1,2-alcoxialcohols, 1,2-aminoalcohols, 1, 2-azidoalcohols, etc [3]. Results and DiscussionAs a part of our ongoing research work concerning the development of organotin reagents for the opening of epoxides [4], the bis(tributyltin) oxide (1) and bis(chlorodibutyltin) oxide (2) were subjected to act as Lewis acids assisting the opening of epoxides in the presence of halogenated alcohols.When styrene oxide was reacted with t-BuOH and 1, the starting material was recovered unchanged after 5 days, probably due to steric hindrances. However, when the same reaction was carried out using the oxide 2, after 3 days a compound was isolated and identified as the chlorohydrin. In this case, bis(chlorodibutyltin) oxide would act as a Lewis acid and, moreover, as a chloride donor.In view of the result described above, we decided to extend the study using a series of halogenated alcohols as a nucleophiles in the presence of the organotin oxides 1 or 2.These results outlined in Scheme 1, shows the formation of the halohydrin derivatives in very good yield by the highly regioselective opening of styrene oxide. However, when the same methodology was applied to other monosubstituted epoxides, the results obtained were different. While the oxide 1, showed a low reactivity towards aliphatic oxiranes, the oxide 2 was able to assist the cleavage of those heterocycles by the nucleophilic attack of the alcohol, or by the chloride anion originated from (ClBu2Sn)2O.The unusual formation of the chlorohydrin compounds would be due to the reaction of the nucleophile with the reagent 2, and the subsequent nucleophilic attack of the chloride over the epoxide.In summary, (ClBu2Sn)2O emerge as a new reagent for the regioselective opening of epoxides yielding the chlorohydrin derivatives, in mild and non-hydrolytic conditions. AcknowledgementsI wish to thanks to Dr. O.A.Mascaretti for his interest and to the Agencia Nacional de Promoción Científica y Tecnológica (SECYT) and Universidad Nacional de Rosario for their financial support.References and NotesSmith, G. J. Synthesis 1984, 629. Schanen, V.; Cherrier, M.; Melo, S.; Quirion, J.; Husson, H. P. Synthesis 1996, 833. Hwang, G.; Chung, J.; Lee, W. J. Org. Chem. 1996, 61, 6183. [PubMed]Salomon, C.J.; Laborde, M.A; Gonzalez Sierra, M.; Mascaretti, O.A. Main Group Metal Chemistry 1998, 21, 617. Share and Cite MDPI and ACS Style Salomon, C.J. Regioselective Opening of Epoxides Catalyzed by Sn (IV). A New Method for the Synthesis of Halohydrins? Molecules 2000, 5, 468-469. https://doi.org/10.3390/50300468 AMA Style Salomon CJ. Regioselective Opening of Epoxides Catalyzed by Sn (IV). A New Method for the Synthesis of Halohydrins? Molecules. 2000; 5(3):468-469. https://doi.org/10.3390/50300468 Chicago/Turabian Style Salomon, Claudio J. 2000. "Regioselective Opening of Epoxides Catalyzed by Sn (IV). A New Method for the Synthesis of Halohydrins?" Molecules 5, no. 3: 468-469. https://doi.org/10.3390/50300468 Find Other Styles Article Metrics No No Article Access Statistics For more information on the journal statistics, click here. Multiple requests from the same IP address are counted as one view.