Novel lipase-catalyzed ring-opening copolymerization of oxiranes and dicarboxylic anhydride forming polyesters bearing carboxyl groups and their physicochemical properties and biodegradability

Oxiranes, such as benzyl glycidate and glycidyl phenyl ether, were copolymerized with dicarboxylic anhydride by lipase at a temperature between 60 and 80 °C to yield the corresponding polyesters bearing carboxyl or phenyl groups. Bulk polymerization, especially at 80 °C, and preferably using porcine pancreatic lipase, gave biodegradable polyesters with a molecular weight of greater than 10000. Poly(sodium carboxylate)s containing ester linkages in the backbone prepared in this study were readily biodegradable by the activated sludge and exhibited a calcium ion sequestration capacity.     

硼酚醛树脂的合成与固化机理的研究

本文研究了硼酚醛树脂的合成与固化反应过程的机理, 结果表明, 甲阶段的硼酚醛树脂主要是硼酸苄酯, 固化过程中形成硼酸苯酯, 反应过程中有醚键生成, 醚键断裂产生羰基。     

Copolymerization of carbon dioxide and propylene oxide using an aluminum porphyrin system and its components

The catalytic activities of tetraphenylporphinatoaluminum chloride (TPPAlCl) and its propylene oxide adduct (TPPAl(PO)₂Cl) were investigated in detail together with a quarternary salt Et₄NBr for the copolymerization of carbon dioxide and propylene oxide. In addition, for the components and starting raw materials of the catalyst systems, catalytic activities were examined for the copolymerization. The TPPAlCl catalyst delivered oligomers containing ether linkages to a large extent, regardless of its PO adduction. And cyclic propylene carbonate, as byproduct, was formed in a very small portion. Using the TPPAlCl coupled with Et₄NBr as a catalyst system, the formation of ether linkages was reduced significantly in the copolymerization; however, the obtained oligomer still contained ether linkages of 25.0 mol % in the backbone. On the other hand, the formation of cyclic carbonate was increased to 22.4 mol % relative to the oligomer product. The results indicate that the salt, which was coupled with the TPPAlCl catalyst, plays a key role in reducing the formation of ether linkage in the oligomer and, however, in enhancing the formation of cyclic carbonate. Similar results were obtained for the copolymerization catalyzed by the TPPAl(PO)₂Cl/Et₄NBr system. That is, the formation of ether linkages was not restricted further by the PO adduction of the TPPAlCl component in the catalyst system. Only oligomers with a relatively high molecular weight were produced. This indicates that the PO adduction of the TPPAlCl component contributes highly to the initiation and propagation step in the oligomerization, consequently leading to a relatively high molecular weight oligomer. In contrast, the Et₄NBr, as well as the Et₂AlCl, produced only cyclic carbonate in a very low yield. Furthermore, tetraphenylporphine exhibited no catalytic activity, regardless of using together with Et₄NBr. On the other hand, the Et₂AlCl coupled with Et₄NBr provided a low molecular weight oligomer having ether linkages of 92.3 mol % in addition to the cyclic carbonate. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3329–3336, 1999     

碳苷研究 V: 用Grignard试剂合成取代苯酚中酚羟基的保护及脱保护

本文报道了一些取代苯酚的合成, 并探讨了用Grignard试剂合成取代苯酚中酚羟基的保护及脱保护的问题. 利用苄基和甲基作为酚羟基的保护基, 对文献报道的切断醚键脱保护方法进行了评价. 找到了两种新体系能在更温和条件下切断醚键的方法, 指出了它们的适用条件. 实验结果符合硬软酸碱理论.     

Vinyl ether end‐groups in poly(ethylene glycol)s from the Na2CO3‐promoted degradation of 1,3‐dioxolan‐2‐one polymers

The Na₂CO₃‐promoted polymerization of 1,3‐dioxolan‐2‐one (I) to afford poly(ethylene glycol) III was reinvestigated. The reaction appeared to involve a nucleophilic attack against the carbonyl and methylene groups of I to afford poly(carbonate) II with poly(ethylene glycol) linkages and ethylene oxide IV as a side product (10–22%). As the reaction progressed, poly(carbonate) II decreased and poly(ethylene glycol) III increased. Under some conditions, poly(ethylene glycol)s V and VI with vinyl ether terminal groups were formed unexpectedly. The formation of unsaturated products during the polymerization of I/EO (ethylene oxide) has not been reported in the literature. We believe that vinyl ethers were formed from the degradation of poly(carbonate)s and were accompanied by a reduction in molecular weight. The structures of vinyl ethers V and VI were confirmed by hydrogenation of the double bond into the ethyl ether group in VII and VIII, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 152–160, 2000     

Synthesis of (+)-juruenolide c: use of sequential 5-exo-digonal radical cyclization, 1,5-intramolecular hydrogen transfer, and 5-endo-trigonal cyclization.

Acetylenic alcohol 10 was converted successively into silane 11 and phenylseleno carbonate 14. On treatment with Ph3SnH, the latter underwent 5-exo-digonal radical cyclization, intramolecular hydrogen transfer, and 5-endo-trigonal cyclization, yielding 15. Conversion of the lactone into the lactol benzyl ether 17, carbon-silicon bond cleavage, and regeneration of the lactone carbonyl gave (+)-juruenolide C (1).     

PHOTOLYSIS OF NITRATE ESTERS—II. SOLUTION PHOTOLYSIS OF ARALKYL NITRATE ESTERS: KINETICS, ESR SPECTRA, AND PHOTOPRODUCTS

Abstract— Irradiation of benzyl nitrate, meso- and dl-hydrobenzoin dinitrates, and cis- and trans -1,2-acenaphthenediol dinitrates in benzene solutions 0.02M in nitrato groups at 265–313 mp decomposed the esters with a quantum yield of 0.4±0.2 in reasonable agreement with earlier work on the gas-phase photolysis of ethyl nitrate. An important primary process was ArRCHONO₂+h v ArRCHO +NO₂, although ArRCHONO₂+h v ArRCHONO + O was not excluded. In secondary reactions solvent benzene was oxidized and nitrated, aldehydes were formed from the nitrate esters, and nitric oxide was evolved. The higher quantum yields of the photodecomposition in ethanol (0.8±0.3) and ether (3±1) solutions were interpreted in terms of a charge-transfer state similar to that found with nitroalkanes in these solvents. Acetaldehyde was produced in a rapid secondary reaction in alcohol solutions at 25° and at 77° K, NO₂ was identified as an intermediate from the ESR spectrum. No stereospecificity was detected in a comparison of rates, photoproducts, and ESR spectra for the stereoisomers. The overall results indicated inter- rather than intramolecular migration of oxy-nitrogen groups in secondary reactions. An apparently new, long-lived, oxynitrogen radical was detected in benzene solutions of nitric oxide and nitrate esters irradiated at 25°.     

Synthesis and properties of a dendritic FRET donor-acceptor system with cationic iridium(III) complex core and carbazolyl periphery

In order to enhance the photoluminescence of cyclometalated iridium(III) complexes, which are potentially useful for biolabeling and bioimaging, a series of benzyl ether branched dendritic moieties with carbazolyl termini were introduced to the cyclometalating C^N ligands of the heteroleptic Ir(III) complexes. The complexes also contain a bidentate bipyridine ligand with a carboxyl group for further bioconjugation or functionalization. The dendritic benzyl ether moieties with carbazolyl peripheral groups have demonstrated a dual function as both a F?rster resonance energy transfer (FRET) donor and an oxygen shield to the Ir(III) complex core. The peripheral carbazolyl groups absorb UV light more intensively and transfer energy efficiently to the Ir(III) complex core via the FRET effect, and thus the photoluminescence of the Ir(III) complex at around 560 nm is significantly enhanced. Furthermore, the benzyl ether dendrimers containing carbazolyl termini can shield the Ir(III) complex core to weaken the oxygen quenching effect, which leads to a further enhancement of the PL of the Ir(III) complex.     

Catalytic Chain Transfer Copolymerization of Propylene Oxide and CO2 using Zinc Glutarate Catalyst

Oligo and poly(propylene ether carbonate)-polyols with molecular weights from 0.8 to over 50 kg/mol and with 60–92 mol % carbonate linkages were synthesized by chain transfer copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) mediated by zinc glutarate. Online-monitoring of the polymerization revealed that the CTA controlled copolymerization has an induction time which is resulting from reversible catalyst deactivation by the CTA. Latter is neutralized after the first monomer additions. The outcome of the chain transfer reaction is a function of the carbonate content, i. e. CO₂ pressure, most likely on account of differences in mobility (diffusion) of the various polymers. Melt viscosities of poly(ether carbonate)diols with a carbonate content between 60 and 92 mol % are reported as function of the molecular weight, showing that the mobility is higher when the ether content is higher. The procedure of PO/CO₂ catalytic chain copolymerization allows tailoring the glass temperature and viscosity.     

A New Oxidative Conversion of Carbohydrate Benzyl Ethers to Benzoyl Esters with RuCl3-NaIO

Abstract

The benzyl group is often used in organic synthesis, especially in carbohydrate chemistry, as one of the most useful of the hydroxyl protecting groups. Benzyl ethers are stable to basic conditions and the benzyl group is removed easily by hydrogenolysis or under Birch reduction conditions. Alternatively, the benzyl ether group is oxidized to benzoyl ester and removed under basic conditions. A few oxidation methods have been reported using more than a stoichiometric amount of chromium reagents such as CrO₃-H₂SO₄ (Jones reagent)¹ or CrO₃-AcOH₂. Here we report a new and mild oxidation of benzyl ether to benzoyl ester with a catalytic amount of RuO₄ derived from RuCl₃ and NaIO₄. This method has proved effective in removing benzyl ether groups chemoselectively in the presence of benzylidene acetal and benzyl glycosidic functions.     

Reactive Polymer as Artificial Solid Electrolyte Interface for Stable Lithium Metal Batteries

Lithium (Li) metal anodes have the highest theoretical capacity and lowest electrochemical potential making them ideal for Li metal batteries (LMBs). However, Li dendrite formation on the anode impedes the proper discharge capacity and practical cycle life of LMBs, particularly in carbonate electrolytes. Herein, we developed a reactive alternative polymer named P(St-MaI) containing carboxylic acid and cyclic ether moieties which would in situ form artificial polymeric solid electrolyte interface (SEI) with Li. This SEI can accommodate volume changes and maintain good interfacial contact. The presence of carboxylic acid and cyclic ether pendant groups greatly contribute to the induction of uniform Li ion deposition. In addition, the presence of benzyl rings makes the polymer have a certain mechanical strength and plays a key role in inhibiting the growth of Li dendrites. As a result, the symmetric Li||Li cell with P(St-MaI)@Li layer can stably cycle for over 900 h under 1 mA cm⁻² without polarization voltage increasing, while their Li||LiFePO₄ full batteries maintain high capacity retention of 96 % after 930 cycles at 1C in carbonate electrolytes. The innovative strategy of artificial SEI is broadly applicable in designing new materials to inhibit Li dendrite growth on Li metal anodes.     

Transparent Films from CO2‐Based Polyunsaturated Poly(ether carbonate)s: A Novel Synthesis Strategy and Fast Curing

Transparent films were prepared by cross‐linking polyunsaturated poly(ether carbonate)s obtained by the multicomponent polymerization of CO₂, propylene oxide, maleic anhydride, and allyl glycidyl ether. Poly(ether carbonate)s with ABXBA multiblock structures were obtained by sequential addition of mixtures of propylene oxide/maleic anhydride and propylene oxide/allyl glycidyl ether during the polymerization. The simultaneous addition of both monomer mixtures provided poly(ether carbonate)s with AXA triblock structures. Both types of polyunsaturated poly(ether carbonate)s are characterized by diverse functional groups, that is, terminal hydroxy groups, maleate moieties along the polymer backbone, and pendant allyl groups that allow for versatile polymer chemistry. The combination of double bonds substituted with electron‐acceptor and electron‐donor groups enables particularly facile UV‐ or redox‐initiated free‐radical curing. The resulting materials are transparent and highly interesting for coating applications.     

Novel lipase-catalyzed ring-opening copolymerization of oxiranes and succinic anhydride forming polyesters bearing functional groups

Oxiranes, such as glycidyl phenyl ether (GPE) and benzyl glycidate (BG), were copolymerized with succinic anhydride (SA) by lipase at a temperature between 60 and 80°C to yield the corresponding polyesters bearing carboxyl or phenyl groups. Bulk polymerization, especially at the temperature of 80°C, and preferably using porcine pancreatic lipase gave biodegradable polyesters with a molecular weight greater than 5000.     

Photoswitchable flexible and shape-persistent dendrimers: comparison of the interplay between a photochromic azobenzene core and dendrimer structure

Two analogous classes of dendrimers with a single azobenzene moiety at the core have been prepared. Flexible benzyl aryl ether dendrimers 1a-e were obtained in good yields by direct alkylation of diphenolic azobenzene 3 with benzyl aryl ether dendrons [G-n]-Br (n = 0-4). In rigid dendrimers 2a-e, the azobenzene configurational switch was linked to phenylacetylene dendrons through acetylenic linkages to maintain the shape-persistent nature of these dendrimers. A comparison of these two different classes of dendrimers with azobenzene cores reveals a difference in the properties of the photochromic moiety upon dendritic incorporation as well as a significant difference in the photomodulation of dendrimer properties. The E --> Z photoisomerization quantum yield decreased markedly with increasing generation for dendrimers 1a-e but only slightly for dendrimers 2a-e. However, increasing generation did not significantly alter thermal isomerization kinetics or activation barriers. The hydrodynamic volumes of azobenzene-containing dendrimers 2b-e were significantly modulated when the azobenzene unit is subjected to irradiation, while those of dendrimers 1b-e were only slightly affected.     

Design, synthesis, and photochemical behavior of poly(benzyl ester) dendrimers with azobenzene groups throughout their architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans-cis isomerization by irradiation and cis-trans isomerization by either irradiation or heating.     

Synthesis of carbonate-containing high temperature poly(arylene-siloxanylenes)

A method for the first synthesis of high molecular weight carbonate-containing siloxanylene polymers was successfully developed. The procedure covered the preparation and polymerization of pure carbonate-containing bis-silanols which included bis(4-hydroxydimethylsilylphenyl)-carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)-phenyl] carbonate, and their meta analogs. Because conventional siloxane polymerization methods, such as the heterocondensation of bis-silanols with diaminosilanes or homocondensation reactions catalyzed by alkali reagents, decomposed carbonate linkages, a new polymerization technique that involved the use of phosgene was used. The procedure was both facile and effective in the polymerization of other arylene bis-silanols.     

醚的初始暗氧化反应机理的研究

有机化合物的空气氧化是一个历史悠久的研究课题。早在1851年Schonbein[1]就注意到醚在空气中会被氧化产生过氧化物。本世纪初,Clover和Milas分析了醚的空气氧化产物,并且对醚的氧化机理,进行了研究。     

Studies in polyphenol chemistry and bioactivity. 3.(1,2) stereocontrolled synthesis of epicatechin-4alpha,8-epicatechin, an unnatural isomer of the B-type procyanidins

Oligomeric procyanidins containing 4alpha-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. We report herein the preparation of the prototypical dimer, epicatechin-4alpha,8-epicatechin (6), by reaction of the protected 4-ketones 11a,b with aryllithium reagents derived by halogen/metal exchange from the aryl bromides 26a,b. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols 27a,b was effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the beta face. If benzyl was chosen for protection of the 3-hydroxyls, all protective groups could subsequently be removed in a single step by hydrogenolysis. tert-Butyldimethylsilyl groups, on the other hand, permitted selective deprotection of the 3-hydroxyls in preparation for their subsequent acylation with tri-O-benzylgalloyl chloride. Only monogalloylation at the "bottom" 3-hydroxyl took place when 28c was acylated under the previously reported conditions, reflecting the increased steric hindrance of the "top" 3-hydroxyl group in 28c compared with its 4beta,8-isomer 3. The preparation of compounds 14 and 17 containing phloroglucinol trimethyl ether in the 4alpha and 4beta linkages to epicatechin is also described. The 8-position of the bromine atom in 19, previously conjectured in analogy to the structurally characterized tetramethyl ether 20, was confirmed by transformation of both compounds into the common derivative 25.     

Protease-mediated fragmentation of p-amidobenzyl ethers: a new strategy for the activation of anticancer prodrugs

A new anticancer prodrug activation strategy based on the 1,6-elimination reaction of p-aminobenzyl ethers is described. Model studies were undertaken with the N-protected peptide benzyloxycarbonyl-valine-citrulline (Z-val-cit), which was attached to the amino groups of p-aminobenzyl ether derivatives of 1-naphthol and N-acetylnorephedrine. The amide bond that formed was designed for hydrolysis by cathepsin B, a protease associated with rapidly growing and metastatic carcinomas. Upon treatment with the enzyme, the Z-val-cit-p-amidobenzyl ether of 1-naphthol (2) underwent peptide bond hydrolysis with the rapid release of 1-naphthol. The aliphatic Z-val-cit-p-amidobenzyl ether of N-acetylnorephedrine (5) also underwent amide bond hydrolysis, but without the ensuing elimination of N-acetylnorephedrine. On the basis of these results, the phenolic anticancer drugs etoposide (6) and combretastatin A-4 (7) were attached to the Z-val-cit-p-amidobenzyl alcohol through ether linkages, forming the peptide-drug derivatives 8 and 9, respectively. Both compounds were stable in aqueous buffers and serum and underwent ether fragmentation upon treatment with cathepsin B, resulting in the release of the parent drugs in chemically unmodified forms. The released drugs were 13-50 times more potent than were the prodrug precursors on a panel of cancer cell lines. In contrast, the corresponding carbonate derivative of combretastatin A-4 (13) was unstable in aqueous environments and was as cytotoxic as combretastatin A-4. This result extends the use of the self-immolative p-aminobenzyl group for the fragmentation of aromatic ethers and provides a new strategy for anticancer prodrug development.     

Effects of poly(ethylene glycol) branch chain linkage mode on polycarboxylate superplasticizer performance

Polycarboxylate superplasticizers (PCs) with ether linkages and ester linkages between the main chains and the poly(ethylene glycol) (PEG) branch chains were synthesized, respectively. The effects of the PCs molecule linkage mode on the performance of concrete paste were investigated using the slump loss test and thermogravimetric analysis and analyzing fluidity, absorption, and setting time. Results showed that the linkage between main chains and PEG branch chains in PCs molecules had an important influence on the performance of cement paste and concrete prepared from them. PCs with ester linkages can endow the cement paste with higher fluidity and higher water‐reduction ratio resulting from the higher absorption amount on the cement particles. This is related with the alternating distribution of the carboxyl groups and branch chains of PEG when different macromonomers are involved in the preparation of PCs. PCs containing ester linkages are more vulnerable than PCs with ether linkages in an alkali environment, leading to quicker slump loss and shorter setting times. In contrast, PCs with ether linkages had excellent fluidity and slump flow stability. A slightly different ettringite hydration product was observed during the early period of the hydration of cement paste that employed these two PCs. Copyright © 2012 John Wiley & Sons, Ltd.