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1.
Nineteen compounds were isolated from the CHCl3 soluble portion of the heartwood of Eucalyptus citriodora. These compounds included trans‐calamenene (1), T‐muurolol (2), α‐cadinol (3), 2β‐hydroxy‐α‐cadinol (4), 4‐hydroxy‐3,5‐dimethoxybenzaldehyde (5), 4‐hydroxy‐3,5‐dimethoxybenzoic acid (6), linoleic acid (7), squalene (8), α‐tocopherol (9), erythrodiol (10), morolic acid (11), betulonic acid (12), cycloeucalenol (13), cycloeucalenol vernolitate (14), β‐sitosterol (15), β‐sitosteryl‐β‐D‐glucopyranoside (16), β‐sitostenone (17), yangambin (18), sesamin (19). Among them, 14 is a new compound. The structures of these compounds were elucidated on the basis of spectroscopic evidence. 相似文献
2.
Dr. Huy N. Hoang Dr. Russell W. Driver Dr. Renée L. Beyer Dr. Timothy A. Hill Dr. Aline D. de Araujo Dr. Fabien Plisson Dr. Rosemary S. Harrison Lena Goedecke Dr. Nicholas E. Shepherd Prof. David P. Fairlie 《Angewandte Chemie (International ed. in English)》2016,55(29):8275-8279
Cyclic pentapeptides (e.g. Ac‐(cyclo‐1,5)‐[KAXAD]‐NH2; X=Ala, 1 ; Arg, 2 ) in water adopt one α‐helical turn defined by three hydrogen bonds. NMR structure analysis reveals a slight distortion from α‐helicity at the C‐terminal aspartate caused by torsional restraints imposed by the K(i)–D(i+4) lactam bridge. To investigate this effect on helix nucleation, the more water‐soluble 2 was appended to N‐, C‐, or both termini of a palindromic peptide ARAARAARA (≤5 % helicity), resulting in 67, 92, or 100 % relative α‐helicity, as calculated from CD spectra. From the C‐terminus of peptides, 2 can nucleate at least six α‐helical turns. From the N‐terminus, imperfect alignment of the Asp5 backbone amide in 2 reduces helix nucleation, but is corrected by a second unit of 2 separated by 0–9 residues from the first. These cyclic peptides are extremely versatile helix nucleators that can be placed anywhere in 5–25 residue peptides, which correspond to most helix lengths in protein–protein interactions. 相似文献
3.
Three new compounds have been isolated from the whole plant of Monochoria vaginalis and characterized as: (2S,3R,4E,8E,2′R)‐1‐O‐(β‐D ‐glucopyranosyl)‐N‐(2′‐hydroxyicosanoyl)‐4,8‐sphingadienine, (2S,3R,4E,8E,2′R)‐1‐O‐(β‐D ‐glucopyranosyl)‐N‐(2′‐hydroxyoctadecanoyl)‐4,8‐sphingadienine and 7‐oxostigmasteryl‐3‐O‐(6′‐hexadecanoyl)‐β‐D ‐glucopyranoside. Their structures were established by spectral and chemical evidence. 相似文献
4.
Dr. Christopher R. Emerson Dr. Lev N. Zakharov Prof. Dr. Paul R. Blakemore 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16342-16356
Four putative functionalized α‐chloroakyllithiums RCH2CHLiCl, where R=CHCH2 ( 18 a ), CCH ( 18 b ), CH2OBn ( 18 c ), and CH[O(CH2)2O] ( 18 d ), were generated in situ by sulfoxide–lithium exchange from α‐chlorosulfoxides, and investigated for the stereospecific reagent‐controlled homologation (StReCH) of phenethyl and 2‐chloropyrid‐5‐yl ( 17 ) pinacol boronic esters. Deuterium labeling experiments revealed that α‐chloroalkyllithiums are quenched by proton transfer from their α‐chlorosulfoxide precursors and it was established that this effect compromises the yield of StReCH reactions. Use of α‐deuterated α‐chlorosulfoxides was discovered to ameliorate the problem by retarding the rate of acid‐base chemistry between the carbenoid and its precursor. Carbenoids 18 a and 18 b showed poor StReCH efficacy, particularly the propargyl group bearing carbenoid 18 b , the instability of which was attributed to a facile 1,2‐hydride shift. By contrast, 18 d , a carbenoid that benefits from a stabilizing interaction between O and Li atoms gave good StReCH yields. Boronate 17 was chain extended by carbenoids 18 a , 18 b , and 18 d in 16, 0, and 68 % yield, respectively; α‐deuterated isotopomers D ‐ 18 a and D ‐ 18 d gave yields of 33 and 79 % for the same reaction. Double StReCH of 17 was pursued to target contiguous stereodiads appropriate for the total synthesis of (?)‐epibatidine ( 15 ). One‐pot double StReCH of boronate 17 by two exposures to (S)‐D ‐ 18 a (≤66 % ee), followed by work‐up with KOOH, gave the expected stereodiad product in 16 % yield (d.r.~67:33). The comparable reaction using two exposures to (S)‐D ‐ 18 d (≤90 % ee) delivered the expected bisacetal containing stereodiad (R,R)‐DD ‐ 48 in 40 % yield (≥98 % ee, d.r.=85:15). Double StReCH of 17 using (S)‐D ‐ 18 d (≤90 % ee) followed by (R)‐D ‐ 18 d (≤90 % ee) likewise gave (R,S)‐DD ‐ 48 in 49 % yield (≥97 % ee, d.r.=79:21). (R,S)‐DD ‐ 48 was converted to a dideuterated isotopomer of a synthetic intermediate in Corey’s synthesis of 15 . 相似文献
5.
Irina Iovel Lena Golomba Sergey Belyakov Juris Popelis Solveiga Grinberga Edmunds Lukevics 《应用有机金属化学》2000,14(11):721-726
The addition of Me3SiCN to Schiff bases 1a–8a, synthesized by the reaction of furan and thiophene aldehydes with 3‐ and 4‐aminobenzotrifluorides, has been studied in the presence of various Lewis acids. A series of the corresponding trifluoromethyl derivatives of heterocyclic α‐aminonitriles 1–8 was synthesized in 38–80% isolated yields. It was found that 4A molecular sieves (MS) accelerate the addition and increase the yields of the products. The investigated catalysts are ranked by their activity in the following order: AlBr3 + 4AMS > AlBr3 > AlCl3 > Ti[O(iPr)]4. A single crystal of N‐(5‐methyl‐2‐thienylcyanomethyl)‐3‐trifluoromethylaniline was obtained and studied by X‐ray diffraction. The results showed that it was the crystal of the (R) isomer of this compound. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
6.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(10):780-783
The molecular conformation and supramolecular architecture of cocaethylene [systematic name: ethyl (1R ,2R ,3S ,5S )‐3‐benzoyloxy‐8‐methyl‐8‐azabicyclo[3.2.1]octane‐2‐carboxylate], C18H23NO4, have been determined for the first time. Cocaethylene is a narcotic produced in vivo when cocaine and ethanol are administered concomitantly. The intra‐ and intermolecular features of cocaethylene and its less potent narcotic precursor cocaine are very similar. The only molecular difference is in the conformation of the methyl group of the ethoxycarbonyl group. Similar to cocaine, the carboxylate atoms and the α‐C atom are coplanar in cocaethylene, but the methyl C atom of the ethyl group is bent by ca 90° away from this plane in the narcotic reported here. The main supramolecular motif is a one‐dimensional chain stabilized by weak C—H…O contacts. 相似文献
7.
Zhan‐Lin Xu Xiao‐Yuan Ma Shuai Ma Xiu‐Yan Wang 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(9):m245-m248
The asymmetric unit of the title compound, [Pb2(C8H4O4)2(C18H11N5)2]n, contains two PbII atoms, two benzene‐1,4‐dicarboxylate (1,4‐bdc) dianions and two 6‐(4‐pyridyl)‐5H‐imidazolo[4,5‐f][1,10]phenanthroline (L) ligands. Each PbII atom is eight‐coordinated by three N atoms from two different L ligands and five carboxylate O atoms from three different 1,4‐bdc dianions. The two 1,4‐bdc dianions (1,4‐bdc1 and 1,4‐bdc2) show different coordination modes. Each 1,4‐bdc1 coordinates to two PbII atoms in a chelating bis‐bidentate mode. Each carboxylate group of the 1,4‐bdc2 anion connects two PbII atoms in a chelating–bridging tridentate mode to form a dinuclear unit. Neighbouring dinuclear units are connected together by the aromatic backbone of the 1,4‐bdc dianions and the L ligands into a three‐dimensional six‐connected α‐polonium framework. The most striking feature is that two identical three‐dimensional single α‐polonium nets are interlocked with each other, thus leading directly to the formation of a twofold interpenetrated three‐dimensional α‐polonium architecture. The framework is held together in part by strong N—H...O hydrogen bonds between the imidazole NH groups of the L ligands and the carboxylate O atoms of 1,4‐bdc dianions within different α‐polonium nets. 相似文献
8.
α‐Imidazolformylarylhydrazine 2 and α‐[1,2,4]triazolformylarylhydrazine 3 have been synthesized through the nucleophilic substitution reaction of 1 with imidazole and 1,2,4‐triazole, respectively. 2,2′‐Diaryl‐2H,2′H‐[4,4′]bi[[1,2,4]‐triazolyl]‐3,3′‐dione 4 was obtained from the cycloaddition of α‐chloroformylarylhydrazine hydrochloride 1 with 1,2,4‐triazole at 60 °C and in absence of n‐Bu3N. The inducing factor for cycloaddition of 1 with 1,2,4‐triazole was ascertained as hydrogen ion by the formation of 4 from the reaction of 3 with hydrochloric acid. 4 was also acquired from the reaction of 3 with 1 and this could confirm the reaction route for cycloaddition of 1 with 1,2,4‐triazole. Some acylation reagents were applied to induce the cyclization reaction of 2 and 3.1 possessing chloroformyl group could induce the cyclization of 2 to give 2‐aryl‐4‐(2‐aryl‐4‐vinyl‐semicarbazide‐4‐yl)‐2,4‐dihydro‐[1,2,4]‐triazol‐3‐one 6. 7 was obtained from the cyclization of 2 induced by some acyl chlorides. Acetic acid anhydride like acetyl chloride also could react with 2 to produce 7D . 5‐Substituted‐3‐aryl‐3H‐[1,3,4]oxadiazol‐2‐one 8 was produced from the cyclization reaction of 3 induced by some acyl chlorides or acetic acid anhydride. The 1,2,4‐triazole group of 3 played a role as a leaving group in the course of cyclization reaction. This was confirmed by the same product 8 which was acquired from the reaction of 1 , possessing a better leaving group: Cl, with some acyl chlorides or acetic acid anhydride. 相似文献
9.
A novel N‐containing compound, vibratilicin (=3‐[3‐(dimethylamino)‐4‐(hydroxyamino)‐4‐oxobutoxy]‐2‐(palmitoyloxy)propyl (9E,12E)‐octadeca‐9,12‐dienoate; 1 ), was isolated from the fruiting bodies of the basidiomycete Cortinarius vibratilis Fr. Compound 1 is a representative of the rare natural products containing hydroxamic acid moieties, and can be viewed as a derivative of neoengleromycin ( 2 ). Also isolated from the same fungus were five known compounds: ergosta‐5,7,22‐trien‐3β‐ol, 5α,8α‐epidioxyergosta‐6,22‐dien‐3β‐ol, p‐anisic acid, N‐(2‐hydroxyhexadecanoyl)‐4‐sphingenine, and (4E,8E)‐2‐N‐(2′‐hydroxypalmitoyl)‐1‐O‐(β‐D ‐glucopyranosyl)‐9‐methyl‐4,8‐sphingadienine. Their structures were determined mainly spectroscopically, including 2D‐NMR techniques (HMBC, HMQC, 1H,1H‐COSY). 相似文献
10.
Boris Minkovich Ilya Ruderfer Alexander Kaushansky Dr. Dmitry Bravo‐Zhivotovskii Prof. Yitzhak Apeloig 《Angewandte Chemie (International ed. in English)》2018,57(40):13261-13265
The first two α‐sila‐dipeptides, 7 and cyclo‐sila‐dipeptide 8 , were synthesized and characterized by several methods, including X‐ray crystallography. Bulky t‐BuMe2Si substituents provide some kinetic stabilization to the synthesized molecules. 7 and 8 are the first examples of a “Si for C switch” in the central α‐position of an amino acid or a peptide, in which silicon is bonded to both the amino and the carbonyl groups. 相似文献
11.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(1):361-368
A synthetic route to enantiomerically pure (1R,2S)‐1‐phenylphospholane‐2‐carboxylic acid ( 1 ), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation–carboxylation of the 1‐phenylphospholane borane complex 3 by using sBuLi/1,2‐dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine‐coordinated α‐phosphinoalkyllithium borane complex 4 , was investigated by employing lithiodestannylation–carboxylation of both diastereomers of the 1‐phenyl‐2‐trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at ?100 °C. The key intermediate, the DPE‐coordinated trans‐1‐phenyl‐2‐phospholanyllithium borane complex 9 , was isolated, and the structure was identified by X‐ray crystal structure analysis. This is the first X‐ray crystal structure determined for an α‐monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li? C bond (2.170 Å) has been confirmed. Moreover, 1H–7Li HOESY and 6Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9 , its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at ?100 °C. Finally, 1 was used as a chiral ligand in a palladium‐catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity. 相似文献
12.
Uk Lee Hea‐Chung Joo Ki‐Min Park Tomoji Ozeki 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(4):m152-m155
The crystal structure of octaguanidinium α‐silicodiplatinodecatungstate hexahydrate, (CH6N3)8[α‐SiPt2W10O40]·6H2O, has been analyzed via a high‐energy X‐ray diffraction experiment at the SPring‐8 BL04B2 beamline. The title compound contains a novel α‐Keggin heteropolyanion in which two of the addenda atoms are replaced by Pt atoms. W and Pt atoms occupy the same coordinates; the occupancy fractions are (W) and (Pt), and the α‐Keggin anion has symmetry. The two types of W(Pt)—W(Pt) distance are in the ranges 3.3565 (4)–3.3704 (4) and 3.7033 (4)–3.7100 (4) Å, the four types of W(Pt)—O bond length are in the ranges 1.721 (5)–1.725 (5), 1.910 (5)–1.932 (5), 1.934 (5)–1.956 (5) and 2.339 (4)–2.348 (4) Å, and the Si—O bond length is 1.646 (4) Å. 相似文献
13.
Bin Wang Dr. Hua‐Ji Liu Xiao‐Bin Fu Prof. Dr. Yefeng Yao Prof. Dr. Yu Chen 《化学:亚洲杂志》2015,10(8):1690-1697
Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI‐IBAm), 4‐(phenylazo)benzoic acid (PABA), and α‐cyclodextrin (α‐CD) were assembled together at pH≈7 to form the three‐component supramolecular complexes that were verified by 1H and 2D ROESY 1H NMR spectroscopy. UV/Vis spectrometric titration experiments showed that the content of α‐CD in the three‐component complexes was less than the feed amount and it was difficult for all the PABA units in the complexes to further form complexes with α‐CD. The obtained three‐component supramolecular complexes exhibited thermoresponsive properties in water. Increasing the α‐CD concentration led to a sharp increase in the cloud point temperature (Tcp) at the beginning, but after the [α‐CD]/[PABA] ratio was in the region of 1.3–1.6, the Tcp increased gradually When the concentration of α‐CD was low, a higher concentration of PABA led to a lower Tcp, however, the opposite was observed when the concentration of α‐CD was high. For the three‐component complex, increasing the α‐CD concentration at pH≈7 or at pH≈9 led to different Tcp temperatures. In the low α‐CD concentration range, adjusting the pH from ≈7–≈9 resulted in an increase in the Tcp, similar but not so pronounced as that of the two‐component system of HPEI‐IBAm/[PABA]. When the concentration of α‐CD was high, adjusting the pH from ≈7–≈9 decreased the Tcp; this observation is different to that of the two‐component system of HPEI‐IBAm/[PABA]. Reversible trans‐to‐cis photoisomerization of azobenzene units in the complexes occurred, following irradiation with UV or visible light. Trans‐to‐cis isomerization of azobenzene units decreased the Tcp. However, this result differed to that of the two‐component system of HPEI‐IBAm/PABA. 相似文献
14.
Francis E. Porbeni I. Daniel Shin Xintao Shuai Xingwu Wang Jeffery L. White Xin Jia Alan E. Tonelli 《Journal of Polymer Science.Polymer Physics》2005,43(15):2086-2096
A biodegradable diblock copolymer of poly(ϵ‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA) was synthesized and characterized. The inclusion compound (IC) of this copolymer with α‐cyclodextrin (α‐CD) was formed and characterized. Wide‐angle X‐ray diffraction showed that in the IC crystals α‐CDs were packed in the channel mode, which isolated and restricted the individual guest copolymer chains to highly extended conformation. Solid‐state 13C NMR techniques were used to investigate the morphology and dynamics of both the bulk and α‐CD‐IC isolated PCL‐b‐PLLA chains. The conformation of the PCL blocks isolated within the α‐CD cavities was similar to the crystalline conformation of PCL blocks in the bulk copolymer. Spin–lattice relaxation time (T1C) measurements revealed a dramatic difference in the mobilities of the semicrystalline bulk copolymer chains and those isolated in the α‐CD‐IC channels. Carbon‐observed proton spin–lattice relaxation in the rotating frame measurements (T1ρH) showed that the bulk copolymer was phase‐separated, while, in the IC, exchange of proton magnetization through spin‐diffusion between the isolated guest polymer chains and the host α‐CD was not complete. The two‐dimensional solid‐state heteronuclear correlation (HetCor) method was also employed to monitor proton communication in these samples. Intrablock exchange of proton magnetization was observed in both the bulk semicrystalline and IC copolymer samples at short mixing times; however, even at the longest mixing time, interblock proton communication was not observed in either sample. In spite of the physical closeness between the isolated included guest chains and the host α‐CD molecules, efficient proton spin diffusion was not observed between them in the IC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2086–2096, 2005 相似文献
15.
Eight new two‐ligand complexes of copper(II) with 1,10‐phenanthroline and one of four different α‐hydroxy‐carboxylic acids (glycolic, lactic, mandelic and benzylic) were prepared. The complexes of general formula [Cu(HL)2(phen)] · nH2O (HL = monodeprotonated acid) ( 1 – 4 ) were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermo‐gravimetric analysis. The complexes of general formulae [Cu(HL)(phen)2](HL) · H2L · nSolv [ 1 a (HL = HGLYO–, n = 1, Solv = MeCN) and 3 a (HL = HMANO–, n = 0)] and [Cu(L)(phen)(OH2)] · nH2O [ 2 a (L = LACO2–, n = 4) and 4 a (L = BENO2–, n = 2)] were characterized by X‐ray diffractometry. In all these latter a pentacoordinated copper atom has a basically square pyramidal coordination polyhedron, the distortion of which towards a trigonal bipyramidal configuration has been evaluated in terms of the parameter τ. In 1 a and 3 a there are three forms of α‐hydroxycarboxylic acid: a monodentate monoanion, a monoanionic counterion, and a neutral molecule lying in the outer coordination sphere; in 2 a and 4 a the α‐hydroxycarboxylic acid is a bidentate dianion coordinating through carboxyl and hydroxyl oxygens. 相似文献
16.
《Journal of separation science》2003,26(14):1263-1268
Interferon α‐2b produced by Escherichia coli consists of 165 amino acids and contains two disulphide bonds; its purity was confirmed by LC‐UV (DAD)‐FLD and LC‐MS techniques. A C4 column was used with UV detection at 214 nm; diode array detector (DAD) spectra were recorded from 200–400 nm and fluorescence detection was performed at specific wavelengths of trypthophan emission and excitation. Peptide mapping was performed with trypsin. Peptides produced by trypsin digestion were analysed by LC‐UV (DAD)‐FLD, LC‐MS, and LC‐MS/MS using a C18 column. Amino acid sequence coverage was about 95%. UV spectra in the range from 200 nm to 400 nm, emission (Em) and excitation (Ex) spectra of each separated peptide were additionally compared with spectra of the same peptide produced by digestion of European Pharmacopaeia interferon α‐2b standard (spectral matching). The chromatogram of any interferon α‐2b (drug substance or certificated standard) sample produced in the same manner with the same amino acid composition should be similar to the chromatogram obtained by the method described in this paper. Molecular masses of peptides were obtained from MS experiments and MS/MS experiments gave additional structural information. The molecular mass of interferon α‐2b was obtained by MALDI‐TOF MS analysis in linear mode, with an accuracy comparable to the theoretical average mass ± 5 atomic mass units. The molecular mass was obtained from the deconvoluted ESI mass spectrum. 相似文献
17.
Hosna Fatahi Mohammad Jafarzadeh Zahra Pourmanouchehri 《Journal of heterocyclic chemistry》2019,56(8):2090-2098
Fe3O4@SiO2–APTES‐supported trifluoroacetic acid nanocatalyst was used for the one‐pot synthesis of α‐aminonitriles via a three‐component reaction of aldehydes (or ketones), amines, and sodium cyanide. This method produced a high yield of 75–96% using only a small amount of the catalyst (0.05 g) in EtOH at room temperature. The catalyst was also employed for the synthesis of 5‐substituted 1H‐tetrazoles from nitriles and sodium azide in EtOH at 80°C. The tetrazoles were produced with good‐to‐excellent yields in a short reaction time of 4 h. Both synthetic methods were carried out in the absence of an organic volatile solvent. Because the supported trifluoroacetic acid generated a solid acid on the surface, thus the acid corrosiveness was not a serious challenge. This heterogeneous nanocatalyst was magnetically recovered and reused several times without significant loss of catalytic activity. 相似文献
18.
Kévin Cocq Nathalie Saffon‐Merceron Yannick Coppel Corentin Poidevin Valérie Maraval Remi Chauvin 《Angewandte Chemie (International ed. in English)》2016,55(48):15133-15136
A ring carbo‐mer of naphthalene, C32Ar8 (Ar=p‐n‐pentylphenyl), has been obtained as a stable blue chromophore, after a 19‐step synthetic route involving methods inspired from those used in the synthesis of carbo‐benzenes, or specifically devised for the present target, like a double Sonogashira‐type coupling reaction. The last step is a SnCl2/HCl‐mediated reduction of a decaoxy‐carbo‐decalin, which is prepared through successive [8+10] macrocyclization steps. Two carbo‐benzene references are also described, C18Ar6 and o‐C18Ar4(C≡C‐SiiPr3)2. The carbo‐naphthalene bicycle is locally aromatic according to structural and magnetic criteria, as revealed by strong diatropic ring current effects on the deshielding of 1H nuclei of the Ar groups and on the negative value of the DFT‐calculated NICS at the center of the C18 rings (?12.8 ppm). The stability and aromaticity of this smallest fused molecular fragment of α‐graphyne allows prediction of the same properties for the carbon allotrope itself. 相似文献
19.
R. Katsarava V. Beridze N. Arabuli D. Kharadze C. C. Chu C. Y. Won 《Journal of polymer science. Part A, Polymer chemistry》1999,37(4):391-407
The purpose of this research was to synthesize new regular poly(ester amide)s (PEAs) consisting of nontoxic building blocks like hydrophobic α‐amino acids, α,ω‐diols, and aliphatic dicarboxylic acids, and to examine the effects of the structure of these building block components on some physico‐chemical and biochemical properties of the polymers. PEAs were prepared by solution polycondensation of di‐p‐toluenesulfonic acid salts of bis‐(α‐amino acid) α,ω‐alkylene diesters and di‐p‐nitrophenyl esters of diacids. Optimal conditions of this reaction have been studied. High molecular weight PEAs (Mw = 24,000–167,000) with narrow polydispersity (Mw/Mn = 1.20–1.81) were prepared under the optimal reaction conditions and exhibited excellent film‐forming properties. PEAs obtained are mostly amorphous materials with Tg from 11 to 59°C. α‐Chymotrypsin catalyzed in vitro hydrolysis of these new PEA substrates was studied to assess the effect of the building blocks of these new polymers on their biodegradation properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 391–407, 1999 相似文献
20.
Combination of ultracentrifugation and solid‐phase extraction with subsequent chromatographic analysis of α‐tocopherol in erythrocyte membranes
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Jiří Plíšek Naďa Pospíchalová Maria Khalikova Jana Aufartová Dagmar Solichová Lenka Kujovská Krčmová Petr Solich 《Journal of separation science》2015,38(4):634-640
A novel and rapid sample pretreatment technique based on a combination of ultracentrifugation and solid‐phase extraction for the determination of α‐tocopherol in human erythrocyte membranes by high‐performance liquid chromatography with ultraviolet detection is presented in this work. Red blood cell samples were ultracentrifuged (288 000 × g, 3 min, 4°C) in the presence of d ‐mannitol, 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid and calcium chloride. The α‐tocopherol was then extracted from the erythrocyte membranes by solid‐phase extraction with n‐hexane in the presence of ascorbic acid. Tocopherol acetate was used as the internal standard. The extract was dissolved in methanol and separated on the monolithic column Chromolith Performance RP‐18e (100 × 4.6 mm) using 100% methanol as the mobile phase. The absorbance of α‐tocopherol was measured at a wavelength of 295 nm. The method was validated and showed sufficient accuracy and precision, ranging from 96.4 to 100.8% and from 4.5 to 6.3%, respectively. Moreover, the developed method was applied to the determination of erythrocyte α‐tocopherol in real samples from patients. The combined ultracentrifugation and solid‐phase extraction technique substantially decreased the time for the sample pretreatment step compared to liquid–liquid extraction and could be applicable for the quantitation of other analytes in erythrocyte membranes. 相似文献