Biomimetic synthesis of petuniasterone D via the epoxy ester[bond]ortho ester rearrangement

The side chain of the insecticidal steroid petuniasterone D was synthesized by the biomimetic acid-catalyzed epoxy ester[bond]ortho ester rearrangement. In addition to the natural (22R,24R)-configuration of the side chain ortho ester, compounds bearing the epimeric (22R,24S)-, (22S,24R)-, and (22S,24S)- [3.2.1]-bicyclic ortho esters were also produced by stereospecific rearrangement of the corresponding isomeric epoxy esters. Functionalization of the steroid nucleus of the (22R,24R)-ortho ester completed the synthesis of the natural product.     

Enzyme labeling in steroid enzyme immunoassays. Comparison of the p-nitrophenyl ester and N-succinimidyl ester methods.

Enzyme labeling of steroids by the p-nitrophenyl ester method was investigated in comparison with the N-succinimidyl ester method. The active ester of a testosterone or 11-deoxycortisol derivative was treated with beta-galactosidase and horseradish peroxidase to give labeled antigens. Various molar ratios of steroid to enzyme and pH conditions were tested. Satisfactory immunoreactivities with an anti-steroid antibody in each enzyme immunoassay system were obtained with the labeled antigens prepared at pH 8.5 by the use of molar ratios higher than 30. The enzyme labeling method should be useful in the case of polar steroids or drugs, since the p-nitrophenyl ester is relatively stable when compared with the N-succinimidyl ester.     

Improved ester interchange catalysts

Mixed alkoxide/aryloxide clusters are long-lived and milder than previously reported ester interchange catalysts. They completely transform difficult substrates in a single synthetic operation with lower catalyst and reagent ester loadings. In addition to superior activities, these mixed clusters are kinetically less basic toward enolizable esters.     

Masked omega-lithio ester enolates: synthetic applications

The protocol of lithiation by means of lithium and a catalytic (5% molar) amount of DTBB (4,4'-di-tert-butylbiphenyl), applied to omega-chloro ortho ester 6 under Barbier-type conditions gives, after final acid-catalyzed methanolysis, the corresponding functionalized esters 8 or 9 (for chlorotrimethylsilane as electrophile) or, after ortho ester deprotection and acid catalyzed treatment, the delta-lactones 11. The procedure is also practical for bicyclic ortho esters 14: the beta-chloro OBO ester derivate generates the gamma- lactones 15 and the gamma-chloro OBO ester gives corresponding esters 8.     

Photoreaction between benzoylthiophenes and N-BOC-tryptophan methyl ester

Drug-induced photoallergy requires as the first step formation of covalent drug-protein photoadducts. One of the key amino acids involved in this process is tryptophan (Trp). In this context, several diaryl ketones, including 2-benzoylthiophene (BT), [2-(5-benzoyl-5-thienyl)]-2-methylpropanoic methyl ester (TPA methyl ester) and 4-(2-thienylcarbonyl)phenyl]-2-methylpropanoic methyl ester (SUP methyl ester) have been irradiated in the presence of N-BOC-(L)-tryptophan methyl ester. Laser flash photolysis has allowed to detect three neutral radicals (ketyl, indolyl and skatolyl radicals) resulting from formal hydrogen-atom abstraction. This correlates well with the isolation of homodimers, as well as with cross-coupling products, in the preparative irradiation. The main cross-coupling products were in all cases lactones arising from the reaction of the Trp-derived skatolyl radicals with the corresponding ketyl radicals. These lactones were obtained as the (4R) stereoisomers with remarkable diasteroselectivity. No coupling products through the phenyl p-position of BT or TPA methyl ester were found. By contrast, ketone homodimers and cross-coupling products arising from reaction through the thienyl 5-position were obtained when using BT and SUP methyl ester; this is very interesting, because stable LAT-derived products are difficult to isolate.     

Ester phenyl-as-triazine and ester phenylquinoxaline polymers

A series of new high molecular weight soluble ester phenyl-as-triazine and ester phenyl-quinoxaline polymers were prepared by solution cyclopolycondensation of oxalamidrazone or 3,3′-diaminobenzidine, respectively, with various bis(benzilyl)esters. Ester groups are incorporated within the backbone of the polymer chain and also as pendant groups on the heterocyclic ring. By TGA in air, initial weight losses for the all-aromatic polyester phenyl-as-triazines and polyester phenylquinoxalines began at ca. 350 and 400°C, respectively. Films of ester phenyl-as-triazine and ester phenylquinoxaline polymers exhibited good thermo-oxidative stability after aging in circulating air at 232 and 288°C, respectively. Two phenylquinoxaline model compounds were also prepared.     

(Meth)acrylate vinyl ester hybrid polymerizations

In this study, vinyl ester monomers were synthesized by an amine catalyzed Michael addition reaction between a multifunctional thiol and the acrylate double bond of vinyl acrylate. The copolymerization behavior of both methacrylate/vinyl ester and acrylate/vinyl ester systems was studied with near‐infrared spectroscopy. In acrylate/vinyl ester systems, the acrylate groups polymerize faster than the vinyl ester groups resulting in an overall conversion of 80% for acrylate double bonds in the acrylate/vinyl ester system relative to only 50% in the bulk acrylate system. In the methacrylate/vinyl ester systems, the difference in reactivity is even more pronounced resulting in two distinguishable polymerization regimes, one dominated by methacrylate polymerization and a second dominated by vinyl ester polymerization. A faster polymerization rate and higher overall conversion of the methacrylate double bonds is thus achieved relative to polymerization of the pure methacrylate system. The methacrylate conversion in the methacrylate/vinyl ester system is near 100% compared to only ～60% in the pure methacrylate system. Utilizing hydrophilic vinyl ester and hydrophobic methacrylate monomers, polymerization‐induced phase separation is observed. The phase separated domain size is in the order of ～1 μm under the polymerization conditions. The phase separated domains become larger and more distinct with slower polymerization and correspondingly increased time for diffusion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2509–2517, 2009     

Polymers from the vinyl ester of dehydroabietic acid

The vinyl ester of dehydrogenated abietic acid has been homopolymerized, copolymerized with vinyl chloride, vinyl acetate, and butadiene and terpolymerized with styrene and acrylonitrile. Both in the homopolymerization and the copolymerization, the vinyl ester of dehydroabietic acid has given lower molecular weight polymers than were obtained with the vinyl ester of tetrahydroabietic acid. Polymers containing the vinyl ester of dehydroabietic acid can be readily crosslinked with peroxide.     

Stereospecific ester activation in nitrite-mediated carbohydrate epimerization

[reaction: see text] The Lattrell-Dax method of nitrite-mediated substitution of carbohydrate triflates is an efficient method to generate structures of inverse configuration. In the present study, epimerization of gluco- and galactopyranoside derivatives to the corresponding allo- and gulopyranoside structures by triflation/nitrite treatment has been investigated. It was found that a neighboring ester group was essential for the reactivity of the nitrite-mediated triflate inversion. Furthermore, a good inversion yield also depended on the relative configuration of the neighboring ester group to the triflate. Only with the ester group in the equatorial position, whatever the configuration of the triflate, did the reaction proceed smoothly, whereas a neighboring axial ester group proved largely inefficient. The results were subsequently used to predict the inversion of glucopyranoside derivatives to the mannopyranoside epimers.     

Ultrasonic and dielectric studies of segmented ester polyurethanes

Ultrasonic and dielectric relaxation measurements are reported as a function of frequency and temperature for a series of segmented ester polyurethanes. Glass transitions for the ester block were determined using a combination of differential scanning calorimetry and dilatometry. The activation energy associated with the dipolar relaxation of the ester group was found to be sensitive to changes in the molecular weight and the relative proportions of the ester and isocyanate in the polymers. These data are discussed with reference to the morphological changes which are known to occur in these systems.     

一定条件下硝酸酯炸药与聚氨酯胶的相互作用研究

用气相质谱(GC-MS)、FTIR对在100℃下处理数十小时后的硝酸酯炸药、聚氨酯胶及二者隔离体系和接触体系的气相组分、凝聚相进行了表征。结果表明:两者直接接触后,彼此之间发生的变化主要由硝酸酯炸药发生分解产生的NO2促使聚氨酯胶的降解并加速自身的分解,聚氨酯胶的降解产物又进一步催化硝酸酯炸药的分解;两者间接接触后,各自释出的气氛对彼此的结构没有影响。     

The preparation and reactions of dienol ester and dienol ester derivatives of hagemann's ester and its t-butyl analogue

The efficient conversion of Hagemann's ester and its t-butyl analogue into dienol ethers and dienol esters, and reactions of the derived dienolates with electrophiles is described.     

Mathematical formulas for ester hydrolysis and formation

Mathematical formulas are developed to describe the progress of ester hydrolysis reactions and the reverse reactions of ester formation, in aqueous solution. Included is a formula for the time to achieve a given degree of reaction. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 277–280, 2001     

Hydrogenation of 2,4-hexadienoic acid methyl ester

Hydrogenation of 2,4-hexadienoic acid methyl ester on supported metal catalysts (Pd/C, Pt/C, Rh/C and Ru/C) has been investigated. Methyl esters of 2-hexenoic and 3-hexenoic acids were formed and further hydrogenated to the methyl ester of hexanoic acid. Palladium was found to be the most active and selective catalyst for this reaction owing to the formation of intermediates.     

Solid-phase synthesis of beta-lactams via the ester enolate-imine condensation route

The ester enolate-imine condensation route to beta-lactams via an immobilized ester enolate has been achieved for the first time. The key reaction in the synthesis is the cyclization of the resin bound ester dianion and an imine. Traceless cleavage from the T1-triazene linker system yields the desired beta-lactams.     

Low frequency elastic modulus measurements on segmented ester polyurethanes

Low frequency extentional modulus measurements are reported as a function of temperature on a series of low isocyanate containing segmented ethyleneadipate diphenyldiisocyanate elastomers. The effects of variation of isocyanate content, molecular weight of the ester block and the ratio of 1, 3 to 1, 4 butanediol chain extender on the glass transition temperatures of the ester phase are explored. The mobility of the ester phase appears to reflect the degree of perfection of the organisation of the urethane phase. The plateau modulus similarly exhibits a correlation with the perfection of the hard phase packing and this is also reflected in the variation of the effective crosslink density obtained from swell measurements. The detailed organisation appears from this study to influence the degree of mobility of the ester phase.     

Dynamic-covalent macromolecular stars with boronic ester linkages

Macromolecular stars containing reversible boronic ester linkages were prepared by an arm-first approach by reacting well-defined boronic acid-containing block copolymers with multifunctional 1,2/1,3-diols. Homopolymers of 3-acrylamidophenylboronic acid (APBA) formed macroscopic dynamic-covalent networks when cross-linked with multifunctional diols. On the other hand, adding the diol cross-linkers to block copolymers of poly(N,N-dimethylacrylamide (PDMA))-b-poly(APBA) led to nanosized multiarm stars with boronic ester cores and PDMA coronas. The assembly of the stars under a variety of conditions was considered. The dynamic-covalent nature of the boronic ester cross-links allowed the stars to reconfigure their covalent structure in the presence of monofunctional diols that competed for bonding with the boronic acid component. Therefore, the stars could be induced to dissociate via competitive exchange reactions. The star formation-dissociation process was shown to be repeatable over multiple cycles.     

Efficient conversion of aldoximes to nitriles using phosphoric acid diethyl ester 2-phenylbenzimidazol-1-yl ester

Abstract  Aromatic aldoximes were converted to the corresponding nitriles in good to excellent yields by employing phosphoric acid diethyl ester 2-phenylbenzimidazol-1-yl ester as reagent. The method was equally effective for oximes bearing electron-donating and electron-withdrawing substituents. Graphical Abstract        

非酯类拟除虫菊酯研究进展

从结构活性关系和合成方面综述了非酯类拟除虫菊酯的研究进展。     

异硫氰酸酯的还原偶联

本文以镁为消耗性电极(阳极), 进行了异硫氰酸酯的电极还原偶联反应的研究, 得到了双分子偶联产物-N, N'-二烃基二硫代草酸胺。