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1.
2-Acetamido-2-deoxypentonolactones were synthesized from per-O-acetylated formazans of d-ribose, d- and l-arabinose, respectively. In dimethyl sulfoxide, a novel spontaneous transformation of the per-O-acetyl-pentose formazans into new 3,4,5-tri-O-acetyl-pent-2-enose formazans has been recognized. Additional examples for the occurrence of the isomerism between pseudo-aromatic chelate and open phenylazo-phenylhydrazone system were demonstrated by 1H NMR spectroscopy in both the unprotected pentose formazans and 3,4,5-tri-O-acetyl-pent-2-enose formazans. Computational calculations supported higher stability of the ring form.  相似文献   

2.
Condensation of 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-α- -galactopyranosyl bromide (3) with methyl 2,3,4-tri-O-acetyl-β- -galactopyranoside (4) gave a fully acetylated (1→6)-β- -galactobiose fluorinated at the 3′-position which was deacetylated to give the title disaccharide. The corresponding trisaccharide was obtained by reaction of 4 with 2,3,4-tri-O-acetyl-6-O-chloroacetyl-α- -galactopyranosyl bromide (5), dechloroacetylation of the formed methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β- -galactopyranosyl)-(1→6)- 2,3,4-tri-O-acetyl-β- -galactopyranoside to give methyl O-(2,3,4-tri-O-acetyl-β- -galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β- -galactopyranoside (14), condensation with 3, and deacetylation. Dechloroacetylation of methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β- -galactopyranosyl)-(1→6)-O-(2,3,4-tri-O-acetyl- β- -galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β- -galactopyranoside, obtained by condensation of disaccharide 14 with bromide 5, was accompanied by extensive acetyl migration giving a mixture of products. These were deacetylated to give, crystalline for the first time, the methyl β-glycoside of (1→6)-β- -galactotriose in high yield. The structures of the target compounds were confirmed by 500-MHz, 2D, 1H- and conventional 13C- and 19F-n.m.r. spectroscopy.  相似文献   

3.
Using MALDI-TOF mass spectrometry, we have shown that leukocytic myeloperoxidase (MPO) in the presence of its substrates (H2O2 and Br?) does not induce any changes in saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Incubation of liposomes prepared from mono-unsaturated phosphatidylcholine (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) with the (MPO + H2O2 + Br?) system resulted in formation of bromohydrins as the main products. 1-Palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (lysophosphatidylcholine) was the main product of the reaction of polyunsaturated phosphatidylcholine (1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine) with the (MPO + H2O2 + Br?) system. The formation of lysophospholipids as well as of bromohydrins was not observed when the enzyme or one of its substrates (H2O2 or Br?) was absent from the incubation medium, or if an inhibitor of MPO (sodium azide) or hypobromite scavengers (taurine or methionine) were added. Thus, it can be postulated that the formation of bromohydrins as well as lysophospholipids by the (MPO + H2O2 + Br?) system results from reactions of hypobromite formed during MPO catalysis with double bonds of acyl chains of phosphatidylcholine. Such destructive processes may take place in vivo in membrane-or lipoprotein-associated unsaturated lipids in centers of inflammation.  相似文献   

4.
The reaction between 2-fluoroadenine (3) and 1,3,5-tri-O-benzyl-1-α-d-chloroarabinofuranose (4) with potassium t-amylate was evaluated in various solvents to afford 9-β-d-(2,3,5-tri-O-benzyl-arabinofuranosyl)-2-fluoroadenine (5) and the corresponding α-anomer (6). In addition, 7-β-d-(2,3,5-tri-O-benzyl-arabinofuranosyl)-2-fluoroadenine (7) and an unusual “bis-fluoroadenine” nucleoside (8) were isolated as by-products. The highest anomeric ratio (β/α > 10) and conversion (>80%) were observed with the highly polar solvent sulfolane. This reaction was demonstrated on gram scale as a practical laboratory synthesis of 5, a known intermediate in the synthesis of fludarabine.  相似文献   

5.
Abstract

Reaction of 2′,3′,5′-O-silylated inosine derivative 1 with 2, 3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH2Cl2-aq. NaOH) system in the presence of Bu4NBr gave three products, i. e., 6-O-α-, 6-O-β-, and N 1-β-isomers of glycosides 4, 5a, and 5b. A similar PTC reaction of 1 with 2, 3, 5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N1-β-glycoside 10. Reaction of 1 with 2, 3, 5-tri-O-benzoylribosyl bromide (11) afforded three products involving the desired N1-β-glycoside 12b, which could be deprotected to give N 1-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.

  相似文献   

6.
The nucleophilic addition–elimination reaction of 2′,3′,5′-tri-O-acetyl-2-fluoro-O 6-[2-(4-nitrophenyl)ethyl]inosine (8) with [15N]benzylamine in the presence of triethylamine afforded the N 2-benzyl[2-15N]guanosine derivative (13) in a high yield, which was further converted into the N 2-benzoyl[2-15N] guanosine derivative by treatment with ruthenium trichloride and tetrabutyl-ammonium periodate. A similar sequence of reactions of 2′,3′,5′-tri-O-acetyl-2-fluoro-O 6-[2-(methylthio)ethyl]inosine (9) and the 6-chloro-2-fluoro-9-(β-D-ribofuranosyl)-9H-purine derivative (11), which were respectively prepared from guanosine, with potassium [15N]phthalimide afforded the N 2-phthaloyl [2-15N]guanosine derivative (15; 62%) and 9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-6-chloro-2-[15N]phthalimido-9H-purine (17; 64%), respectively. Compounds 15 and 17 were then efficiently converted into 2′,3′,5′-tri-O-acetyl[2-15N]guanosine. The corresponding 2′-deoxy derivatives (16 and 18) were also synthesized through similar procedures.  相似文献   

7.
A novel 1,2-cis stereoselective synthesis of protected α-d-Gal-(1→2)-d-Glc fragments was developed. Methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranoside (13), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-α-d-glucopyranoside (15), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (17), and methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-d-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-β-d-glucopyranoside (19) were favorably obtained by coupling a new donor, isopropyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-1-thio-β-d-galactopyranoside (2), with acceptors, methyl 3-O-benzoyl-4,6-O-benzylidene-α-d-glucopyranoside (4), methyl 3,4,6-tri-O-benzoyl-α-d-glucopyranoside (5), methyl 3-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (8), and methyl 3,4,6-tri-O-benzoyl-β-d-glucopyranoside (12), respectively. By virtue of the concerted 1,2-cis α-directing action induced by the 3-O-allyl and 4,6-O-benzylidene groups in donor 2 with a C-2 acetyl group capable of neighboring-group participation, the couplings were achieved with a high degree of α selectivity. In particular, higher α/β stereoselective galactosylation (5.0:1.0) was noted in the case of the coupling of donor 2 with acceptor 12 having a β-CH3 at C-1 and benzoyl groups at C-4 and C-6.  相似文献   

8.
A series of new N′-[N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)thiocarbamoyl]-2-[(1-aryl-1H-tetrazol-5-yl)sulfanyl]acetohydrazides 5a5e were synthesized rapidly in high yields from 2-(1-aryl-1H-tetrazol-5-ylsulfanyl)acetohydrazides 3a3e and 2,3,4-tri-O-acetyl-β-d-xylopyranosyl isothiocyanate 4, then 5a5e were converted to a series of new 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-oxadiazole-2-amines 6a6e and 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-thiadiazole-2-amines 7a7e, respectively under mercuric acetate/alcohol system or acetic anhydride/phosphoric acid system, then deacetylated in the solution of CH3ONa/CH3OH. All of the novel compounds were characterized by IR, 1H NMR, 13C NMR, MS and elemental analysis. The structures of compounds 2e, 3e, 5a and 5c have been determined by X-ray diffraction analysis. Some of the synthesized compounds displayed PTP1B inhibition and microorganism inhibition.  相似文献   

9.
《Free radical research》2013,47(4):217-226
The non-toxic and water soluble dihydroquinoline type antioxidants: CH 402 (Na-2,2-dimethyl-l.2-dihydroquinoline-4-yl methane sulphonate) and MTDQ-DA (6.6-methylene bis 2.2-dimethyl-4-methane sulphonicacid: Na-1.2-dihydroquinoline) were studied in various in vitro tests in which oxygen free radicals were generated. Both compounds were shown to scavenge superoxide radical anions O?2 produced in aqueous solution by pulse radiolysis with rate constants k (O?2 + MTDQ-DA) = 4.108dm3 mol?1s?1 and k(O?2 +CH402) = 1.5.107dm3 mol?1s ?1. CH 402 and MTDQ-DA reduced the H2O2 produced in the glucose-glucose oxidase reaction, which was detected by the luminol + hemin reaction with a chemilumi-nometric method. The dihydroquinoline type substrates inhibited the NADPH-induced and Fe3 +—stimulated lipid peroxidation and the ascorbic acid-induced non-enzymatic peroxidation pathways in microsomal fractions of rat and mouse liver.  相似文献   

10.
Abstract

Zofenopril as an ACE inhibitor expired recently was found to have a favourable safety profile in comparison with other ACE inhibitors in treating high blood pressure, congestive heart failure, and acute myocardial infarction. It can be synthesised from the key building blocks of (S)-3-benzoylthio-2-methylpropanoic acid and (4S)-phenylthio-L-proline. In this report, an efficient hydrolytic resolution via Candida antarctic lipase B (CALB) for preparing the former block in isopropyl ether (IPE) containing (RS)-3-benzoylthio-2-methylpropyl pyrazolide (1) and water was developed. Quantitative improvements of the enzyme activity and enantioselectivity in terms of k2SKmS?1?=?5.726?L h?1 g?1 and E?=?217 at 45?°C were found from the kinetic analysis. Insights into the CALB performance via thermodynamic analysis were then addressed and compared with those by using (RS)-3-benzoylthio-2-methylpropyl 1,2,4-triazolide (2) as the substrate. A putative thermodynamic model was moreover hypothesised for elucidating the more enthalpy reduction of 68.92-70.86?kJ mol?1 from the acyl part of (S)-1 and (S)-2 as well as that of 23.69-25.63?kJ mol?1 from the triad imidazolium to Ser105 and leaving 1,2,4-triazole moiety of (R)-2 and (S)-2 on stabilising the corresponding transition states.  相似文献   

11.
12.
O-α- -Rhamnopyranosyl-(1→3)- -rhamnopyranose (19) and O-α- -rhamnopyranosyl-(1→2)- -rhamnopyranose were obtained by reaction of benzyl 2,4- (7) and 3,4-di-O-benzyl-α- -rhamnopyranoside (8) with 2,3,4-tri-O-acetyl-α- -rhamnopyranosyl bromide, followed by deprotection. The per-O-acetyl α-bromide (18) of 19 yielded, by reaction with 8 and 7, the protected derivatives of the title trisaccharides (25 and 23, respectively), from which 25 and 23 were obtained by Zemplén deacetylation and catalytic hydrogenolysis, With benzyl 2,3,4-tri-O-benzyl-β- -galactopyranoside, compound 18 gave an ≈3:2 mixture of benzyl 2,3,4-tri-O-benzyl-6-O-[2,4-di-O-acetyl-3-O-(2,3,4-tri-O-acetyl-α- -rhamnopyranosyl)-α- -rhamnopyranosyl]-β- -galactopyranoside and 4-O-acetyl-3-O-(2,3,4-tri-O-acetyl-α- -rhamnopyranosyl)-β- -rhamnopyranose 1,2-(1,2,3,4-tetra-O-benzyl-β- -galactopyranose-6-yl (orthoacetate). The downfield shift at the α-carbon atom induced by α- -rhamnopyranosylation at HO-2 or -3 of a free α- -rhamnopyranose is 7.4-8.2 p.p.m., ≈1 p.p.m. higher than when the (reducing-end) rhamnose residue is benzyl-protected (6.6-6.9 p.p.m.). α- -Rhamnopyranosylation of HO-6 of gb- -galactopyranose deshields the C-6 atom by 5.7 p.p.m. The 1 2-orthoester ring structure [O2,C(me)OR] gives characteristic resonances at 24.5 ±0.2 p.p.m. for the methyl, and at 124.0 ±0.5 p.p.m. for the quaternary, carbon atom.  相似文献   

13.
Abstract

Ribosylation reactions of previously silylated 3-carbethoxy-8-methyl-1,4-dihydro-4-oxoquinoline (6a) and 3-carbethoxy-6-methyl-1,4-dihydro-4-oxoquinoline (6b) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose (7), under Lewis acid catalysis, were studied. The method using hexamethyldisilazane (HMDS)/trimethylchlorosilane (TMCS) mixture for silylation and anhydrous stannic chloride as catalyst for ribosylation failed to give any nucleoside product. On the other hand, the protected nucleoside 3-carbethoxy-6-methyl-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-1,4-dihydro-4-oxoquinoline (8b) was obtained in good yields using bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% of TMCS and the same catalyst. Compound 8b was more easily isolated in higher yields with an improvement of the later method by replacing stannic chloride with trimethylsilyl trifluoromethanesulfonate (TMSOTf).

De-O-benzoylation of 8b with methanolic sodium hydroxide solution afforded the free riboside 3-carbomethoxy-6-methyl-1-β-D-ribofuranosyl-1,4-dihydro-4-oxoquinoline (9b). The structures of the obtained products were confirmed by their LTV, MS, IR, 1H and 13C-NMR data.  相似文献   

14.
The heme-based oxygen-sensor enzyme from Escherichia coli (Ec DOS) is a heme-regulated phosphodiesterase with activity on cyclic-di-GMP and is composed of an N-terminal heme-bound sensor domain with the PAS structure and a C-terminal functional domain. The activity of Ec DOS is substantially enhanced by the binding of O2 to the Fe(II)-protoporphyrin IX complex [Fe(II) complex] in the sensor domain. The binding of O2 to the Fe(II) complex changes the structure of the sensor domain, and this altered structure becomes a signal that is transduced to the functional domain to trigger catalysis. The first step in intra-molecular signal transduction is the binding of O2 to the Fe(II) complex, and detailed elucidation of this molecular mechanism is thus worthy of exploration. The X-ray crystal structure reveals that Phe113 is located close to the O2 molecule bound to the Fe(II) complex in the sensor domain. Here, we found that the O2 association rate constants (>200 × 10−3 μM−1 s−1: F113L; 26 × 10−3 μM−1 s−1: F113Y) of the Fe(II) complexes of Phe113 mutants were markedly different from that (51 × 10−3 μM−1 s−1) of the wild-type enzyme, and auto-oxidation rates (0.00068 min−1: F113L; 0.039 min−1: F113Y) of the Phe113 mutants also differed greatly from that (0.0062 min−1) of the wild-type enzyme. We thus suggest that Phe113, residing near the O2 molecule, has a critical role in optimizing the Fe(II)-O2 complex for effective regulation of catalysis by the oxygen-sensor enzyme. Interactions of CO and cyanide anion with the mutant proteins were also studied.  相似文献   

15.
Ribulose-1,5-bisphosphate (RuBP) pool size was determined at regular intervals during the growing season to understand the effects of tropospheric ozone concentrations, elevated atmospheric carbon dioxide concentrations and their interactions on the photosynthetic limitation by RuBP regeneration. Soybean (Glycine max [L.] Merr. cv. Essex) was grown from seed to maturity in open-top field chambers in charcoal-filtered air (CF) either without (22 nmol O3 mol?1) or with added O3 (83 nmol mol?1) at ambient (AA, 369 μmol CO2 mol?1) or elevated CO2 (710 μmol mol?1). The RuBP pool size generally declined with plant age in all treatments when expressed on a unit leaf area and in all treatments but CF-AA when expressed per unit ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) binding site. Although O3 in ambient CO2 generally reduced the RuBP pool per unit leaf area, it did not change the RuBP pool per unit Rubisco binding site. Elevated CO2, in CF or O3-fumigated air, generally had no significant effect on RuBP pool size, thus mitigating the negative O3 effect. The RuBP pools were below 2 mol mol?1 binding site in all treatments for most of the season, indicating limiting RuBP regeneration capacity. These low RuBP pools resulted in increased RuBP regeneration via faster RuBP turnover, but only in CF air and during vegetative and flowering stages at elevated CO2. Also, the low RuBP pool sizes did not always reflect RuBP consumption rates or the RuBP regeneration limitation relative to potential carboxylation (%RuBP). Rather, %RuBP increased linearly with decrease in the RuBP pool turnover time. These data suggest that amelioration of damage from O3 by elevated atmospheric CO2 to the RuBP regeneration may be in response to changes in the Rubisco carboxylation.  相似文献   

16.
Two phenoxido bridged dinuclear Cu(II) complexes, [Cu2(L1)2(NCNCN)2] (1) and [Cu2(L2)2(NCNCN)2]·2H2O (2) have been synthesized using the tridentate reduced Schiff-base ligands 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL1) and 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL2), respectively. The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both the complexes present a diphenoxido bridging Cu2O2 core. The geometries around metal atoms are intermediate between trigonal bipyramid and square pyramid with the Addison parameters (τ) = 0.57 and 0.49 for 1 and 2, respectively. Within the core the Cu–O–Cu angles are 99.15° and 103.51° and average Cu–O bond distances are 2.036 and 1.978 Å for compounds 1 and 2, respectively. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = −184.3 and −478.4 cm−1 for 1 and 2, respectively) differ appreciably.  相似文献   

17.
The substrate-inhibitory analysis has shown that single “atypical” cholinesterase (ChE) presents in tissues of freshwater oligochaete Lumbriculus variegatus (O.F. M?ller). This enzyme differs both from “typical” acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Specific activity of oligochaete ChE ranges 55–100 μmol ATCh g−1 tissue min−1 or 0.7–1 μmol ATCh mg−1 protein min−1, ratio of maximal rates (V) of substrate hydrolysises is 100:72:71:83 for acetyl-, propionyl-, butyryl- and acetyl-β-metylthiocholine respectively. Values of Michaelis constant (Km) for these substrates are (1.9–2.5) × 10−4 M. The bimolecular enzyme inhibition rate constants (kII) for organophosphorus inhibitors paraoxon, DDVP, and iso-OMPA are 107, 106 и 103 mol−1 | min−1. ATCh and BuTCh exhibit the effect of substrate inhibition of ChE activity, while PrTCh and MeTCh do not.  相似文献   

18.
The reaction of Ru(XTPP)(DMF)2, where XTPP is the dianion of para substituted tetraphenylporphyrins and X is MeO, Me, H, Cl, Br, I, F, with O2 and CO were studied in DMF. The process was found to be first-order in metalloporphyrin, first-order in molecular oxygen and carbon monoxide, and second-order overall. Second-order rate constants for the CO reaction ranged from 0.170 to 0.665 M?1 s?1 at 25°C, those for the O2 reaction from 0.132 to 0.840 M?1 s?1 at 25°C. Similar activation parameters (ΔHCO± = 87 ± 1 kJ mol?1, ΔSCO± = 22 ± 4 JK?1 mol?1; ΔHO2± = 81 ± 1 kJ mol?1, and ΔSO2± = 11 ± 5 JK?1 mol?1) were found within each series. Reactivities of X substituted metalloporphyrins were found to follow different Hammett σ functions. The CO reactions correlated with σ? following normal behavior; the O2 reactions correlated with σ8° indicating O2 is π-bonded in the transition states. A dissociative mechanism is postulated for the process.  相似文献   

19.
The linkage isomers, (OC)5M[κ1-PPh2 CH2CH(PPh2)2] 1 and (OC)5M[κ1-PPh2 CH(PPh2)CH2PPh2] 2 (M = Cr, Mo and W) exist in equilibrium at room temperature. Equilibrium constants for 1Cr ? 2Cr, 1Mo ? 2Mo and 1W ? 2W at 25 °C in CDCl3 are 2.61, 5.0 and 4.74, respectively. Enthalpy favors the forward reaction (ΔH = −13.5, −12 and −12.2 kJ mol−1, respectively) while entropy favors the reverse reaction (ΔS = −37.6, −28 and −28.2 J K−1 mol−1, respectively). Isomerization is much faster than chelation with 1Mo ? 2Mo ? 1W ? 2W > 1Cr ? 2Cr. Enthalpies of activation for 1Cr ? 2Cr and 1W ? 2W are 119.0 and 92.6 kJ mol−1, respectively, and entropies of activation are 1.4 and −28.2 J K−1 mol−1, respectively. Isomerization is 104 times faster for these complexes than for (OC)5M[κ1-PPh2CH2CH2P(p-tolyl)2]. A novel mechanism is proposed to account for the rate differences. The X-ray crystal structure of 2W shows that the phosphorus atom of the short phosphine arm lies very close to a carbon atom of the W(CO)4 equatorial plane (3.40 Å) which could allow “through-space” coupling, accounting in part for the observation of long-range JPC and JPW coupling. The X-ray structure of (OC)5W[κ1-PPh2 C(CH2)PPh2] 5W has been determined for comparison to 2W.  相似文献   

20.
ABSTRACT

A novel synthesis of a new class of 2-(β-D-ribofuranosylthio)pyridine glycosides utilizing the reactions of substituted pyridine-2(1H)-thiones and 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose as starting components is described.  相似文献   

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