A new enzyme catalysis: 3,4-dioxidation of some aryl β-d-glycopyranosides by fungal pyranose dehydrogenase

Quinone-dependent pyranose dehydrogenase presents a new tool for versatile conversions of numerous carbohydrates to their di- and tricarbonyl derivatives. This enzyme purified from the basidiomycete Agaricus meleagris catalysed dioxidation of several aromatic β-d-glucopyranosides and a β-d-xylopyranoside into the corresponding 3,4-didehydro-β-d-aldopyranosides (β-d-aldopyranosid-3,4-diuloses) in high yields, typically >80% for 4-nitrophenyl glycosides. These new compounds were doubly hydrated in aqueous solution. According to in situ NMR investigations, the reaction intermediates were the corresponding 3- and 4-dehydro compounds. The analogous anomeric α-glycosides underwent one-step oxidation only at C-3 to 3-dehydro-α-d-aldopyranosides (α-d-pyranosid-3-uloses).     

Intramolecular 1,8-hydrogen atom transfer reactions in disaccharide systems containing furanose units

A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4-C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric d-furanoses. d-xylo- and d-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas d-arabino- and d-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively.     

Concerning a new glycoside preparation method. Synthesis of epidopodophyllotoxin-beta-D-glucopyranoside

A new method for the synthesis of glycosides is described. Epipodophyllotoxin ( 4 ) reacts with 2,3,4,6-tetra-O-acetyl-β-D -glucopyranose in the presence of BF₃-etherate at low temperature to yield tetra-O-acetyl-epipodophyllotoxin-β-D -glucopyranoside ( 6 ). This compound, which is sensitive to acid and base, can be converted into the free glucoside 8 by zinc acetate catalysed methanolysis. Glycosidation of podophyllotoxin ( 1 ) occurs under the same conditions but is associated with an inversion at C-1 of the aglycone moiety, leading also to the acetylated epi-glucoside 6 . It is assumed that the glycosidation proceeds through a common carbonium ion intermediate ( 12 ), generated from 1 and 4 respectively by the action of BF₃. The intermediate 12 is substituted by the pyranose component from the less hindered side, giving exclusively 1-epi derivatives (e.g. 6 ). The glycosidation reaction is also highly stereoselective with respect to the glycosidic linkage. The stereochemistry of this bond is determined by the configuration at C-1 of the pyranose compound employed for the glycosidation. Further experimental evidence for the proposed mechanism consists in the glycosidation of diphenylmethanol ( 14 ) to the corresponding β-D -glucoside 15 . Scope and limitation of the new glycosidiation method are briefly discussed.     

PMR investigation into the structure of some n-substituted 1-amino-1-deoxy-D-fructoses (amadori rearrangement products) : Evidence for a preferential conformation in solution

The PMR spectra at 220 MHz of some Amadori rearrangement products deduced from D-glucose with p-toluidine (1), N-methylphenylamine (2), di-butylamine (4), piperdine (5), and morpholine (6) have been studied in detail.Compounds 1-6 appear to exist in solution predominantly as an equilibrium mixture of the furanose and pyranose ring. The pyranose ring occurs exclusively in the β(D)-²C₅-conformation (corresponds to Reeves 1C-conformation). The furanose ring probably exists as a mixture of both the β- and α-anomer, in which the β-anomer is favoured.     

Structures of novel norstilbene dimer, longusone A, and three new stilbene dimers, longusols A, B, and C, with antiallergic and radical scavenging activities from Egyptian natural medicine Cyperus longus

The methanolic extract of the whole plant of Cyperus longus originating in Egypt was found to show antiallergic effect on ear passive cutaneous anaphylaxis reactions in mice. By bioassay-guided separation, 11 stilbenes and stilbene dimers including a novel norstilbene dimer, longusone A, and three new stilbene dimers, longusols A, B, and C, were isolated. Their structures were elucidated on the basis of chemical and physicochemical evidence. Among the isolates, longusol B (IC(50)=96 μM), luteolin (3.0 μM), resveratrol (17 μM), piceatannol (24 μM), and cassigarols E (84 μM) and G (84 μM) were found to inhibit the release of β-hexosaminidase, as a marker of antigen-induced degranulations, in rat basophilic leukemia (RBL-2H3) cells. In addition, the methanolic extract and the constituents showed 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (SC(50)=22 μg/ml and 2.8-29 μM, respectively).     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献   

The first ring inversion of pyranoses induced by bulky silyl protections at the 2- and 3-positions

The pyranose rings of the 2,3-bis-O-tert-butyldiphenylsilyl-α- and β-d-glucopyranoses, and of the 2,3-bis-O-tert-butyldimethylsilyl-β-d-glucopyranose were in the ¹C₄ form. These findings indicate that the introduction of bulky silyl protecting groups at the 2- and 3-positions can flip a pyranose ring into the axial-rich chair form. Previous such ring inversions have been carried out by the silyl protections at the 3- and 4-positions.     

Réactions inhabituelles dans la synthèse et la substituition d'un triflate osdique

Triflation of methyl 3-azido-3,4-dideoxy-α or β-DL-threo-pentopyranoside with triethylamine as acid acceptor in dichloromethane, gave the two isomers of a 1:2′ , 2:1′ dianhydride. Benzoate displacement of the α triflate occured with a pyranose to furanose contraction reaction at C-2.     

Multiple component approaches to C-glycosyl beta-amino acids by complementary one-pot Mannich-type and Reformatsky-type reactions

The development of new methods for the preparation of C-glycosyl beta-amino acid libraries with chemical and stereochemical diversity levels was investigated and the results are described herein. Two complementary one-pot three-component Mannich-type and Reformatsky-type synthetic strategies have been developed for the construction of chiral 3-amino propanoate fragments (eventually bis-substituted at C-2) directly linked to the anomeric carbon of pyranose and furanose residues. Both methods involved as the initial step the coupling of a sugar aldehyde to p-methoxybenzylamine but differed in the nucleophile (a d(2) synthon equivalent) which was successively added: a ketene silyl acetal (Mannich route) or a bromozinc enolate (Reformatsky route). Individual C-glycosyl beta-amino esters were isolated as single 3R diastereoisomers in fair to excellent yield (60-90%) and their structure assigned by NMR spectroscopy (Riguera protocol) supported by X-ray crystallography. A tentative explanation of the observed stereochemical outcome based on transition-state models is provided. A preliminary study on the synthesis of alpha,alpha-difluoro C-glycosyl beta-amino acids via a more traditional Reformatsky route is also reported.     

Crystal Structures of Methyl (Methyl 3-azido-2,3-dideoxy-β-L-lyxo- and -β-D-arabino-hexopyranosid)uronates

Single-crystal x-ray diffraction data for methyl (methyl 3-azido-2,3-dideoxy-β-L-lyxo- and β-D-arabino-hexopyranosid)uronates are presented. Three independent molecules in the asymmetric part of the unit cell of the β-D-arabino stereoisomer were found. These differ slightly in the geometry of the groups bound to the pyranose rings. Conformations and the geometry parameters of all the molecules as well as the planarity of the carbomethoxy group, the linearity of the azido group, and the orientation of the aglycone in the crystal lattice are discussed. Influence of the hybridization, resonance, and crystal packing on the geometry parameters is shown.     

Synthesis of an adenine nucleoside containing the (8'R) epimeric carbohydrate core of amipurimycin and its biological study

The (8'R) epimeric carbohydrate core 2 of amipurimycin was synthesized from D-glucose derived allylic alcohol 3 in 11 steps and 13% overall yield. The key steps involve an acid-catalyzed acetonide ring opening of 9 with concomitant formation of an unprecedented pyranose ring skeleton to give 2,7-dioxabicyclo[3.2.1]octane 10. The α-orientation of the furan ring in 10 readily allows the stereoselective β-glycosylation and opening of the furanose ring that on removal of protecting groups affords the pyranosyl adenine nucleoside 2. The antifungal and anticancer activities of 2 were studied.     

Crystal Structure of 1，6：3，4－Dianhydro－β－D－galactopyranose－2－O－p－tolylsulfonate（C_13H_14O_6S）

ＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅｏｆ１，６：３，４－Ｄｉａｎｈｙｄｒｏ－β－Ｄ－ｇａｌａｃｔｏｐｙｒａｎｏｓｅ－２－Ｏ－ｐ－ｔｏｌｙｌｓｕｌｆｏｎａｔｅ（Ｃ_１３Ｈ_１４Ｏ_６Ｓ）ＷａｎｇＡｎ－Ｌａｉ；ＬｕＳｈｉ－Ｊｉｅ；ＦｕＨｏｎｇ－Ｘｉａｎｇ；Ｗａ?..     

Competitive Host-guest Electrochemical Detection of Ivermectin Drug Using a β-Cyclodextrin/Graphene-based Electrode

The present study describes the novel development and application of an ivermectin (IVM) sensing electrochemical platform based on reduced graphene oxide (rGO) and the macrocyclic host β-cyclodextrin (β-CD) molecule. The sensing method was based in the host-guest characteristics of β-CD and competitive interaction between the target analyte and the methylene blue (MB) redox probe. Differential pulse voltammetry (DPV) was employed for the detection of IVM and a linear response between 0.5 and 40.0 μmol L⁻¹ with a limit of detection of 0.25 μmol L⁻¹ was obtained using the glassy carbon (GC)/rGO/β-CD electrode. The sensing platform was successfully applied for the detection of IVM in tap water samples, which may expand the applications of β-CD towards the analysis of other chemical species.     

Synthesis of Mono- and Disaccharide 4-[(ω-Sulfanylalkyl)oxy]benzoylhydrazones as Potential Glycoligands for Noble Metal Nanoparticles

A procedure has been developed for the synthesis of previously unknown aldose 4-[(ω-sulfanylalkyl) oxy]benzoylhydrazones (where alkyl is hexyl or decyl and aldoses are D-glucose, D-galactose, D-maltose, and D-lactose) that a repromising glycoligands for noble metal nanoparticles. According to the ¹H and ¹³C NMR data, 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones derived from D-glucose, D-maltose, and D-lactose in crystal and in DMSO-d₆ solution have exclusively the cyclic pyranose structure (α- and β-anomers). D-Galactose 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones in DMSO-d₆ solution exist as tautomeric mixtures of cyclic pyranose and open-chain acylhydrazone structures.

     

双(N 氧化吡啶 2-甲醛)缩1,2-丙二胺镍配合物的合成和晶体结构

合成所得双(N-氧化吡啶-2-甲醛)缩1,2-丙二胺的镍(II)配合物[Ni(piopn)(H_2O)_2](ClO_4)_2的晶体属空间群C_s~4-C_c, 晶胞参数a=0.7397(3) nm, b=1.3187(7) nm, c=2.5502(14) nm, β=102.18(4)°. 用分子轨道理论的近似方法分析了该配合物的电子结构和分子轨道, 探讨了分子的结构特征与红外光谱的关系.     

Chiral Phosphine Ligands Derived from Sugars. 14. Crystal Structure of Diphenyl(methyl 4',6'-O-benzylidene-3'-deoxy-α-D-altropyranoside-3-)phosphine Oxide

The crystal structure of the title compound, C26H27O6P, has been determined by single-crystal X-ray diffraction analysis. The crystal is orthorhombic with space group P212121, a=6.154(4), b=17.199(8), c=22.180(3)(A), V=2347.6(A)3, Dc=1.32 g/cm3, F(000)=984, μ=1.5cm-1, Z=4, and final R=0.075 and Rw=0.080 for 1417 reflections (I≥3σ(I)). The X-ray diffraction analysis revealed that the structure of the title compound s similar to that of its parent phosphine and the pyranose and 4, 6-O-benzylidene rings remain distorted chair conformations.     

不同晶型Bi2O3可见光光催化降解罗丹明B的研究

采用化学沉淀法制备了α、β、γ 3种晶体结构的Bi₂O₃光催化剂。利用XRD、TEM、氮气吸附、TG-DSC、紫外-可见漫反射光谱对样品的晶体结构、微观形貌、光学吸收特性进行了表征,并以罗丹明B(RhB)作为模型污染物,研究了不同的粉体光催化剂在可见光(λ>420 nm)照射下的光催化能力。结果表明：制备的α-Bi₂O₃为长3 μm、宽1 μm的板条状颗粒,带隙为2.84 eV;β-Bi₂O₃为粒径约150 nm的不规则颗粒,带隙为2.75 eV;γ-Bi₂O₃为直径6 nm、长度150~200 nm的纳米管,带隙为2.68 eV。在可见光照射下Bi₂O₃光催化降解RhB的活性如下：γ-Bi₂O₃>β-Bi₂O₃>α-Bi₂O₃,其中γ-Bi₂O₃在辐照60 min后对罗丹明B的脱色率可达97%以上。     

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.     

Stereoselective synthesis of C-glycosylphosphonates from their ketols. Reconsideration of an abandoned route

Isosteric phosphonate analogues of glycosyl 1-phosphates have been obtained by addition of LiCH₂P(O)(OMe)₂ to glyconolactones followed by Et₃SiH–TMSOTf reductive dehydroxylation of the resultant ketols. The compounds prepared include four β-linked pyranose derivatives (d-galacto, 2-azido-2-deoxy-d-galacto, d-gluco, d-manno) and one β-linked furanose derivative (d-manno). In the latter case the ketol was activated as its 2-acetate. In agreement with an observation in another laboratory, the dehydroxylation of a model ketol phosphonate failed with the use of Et₃SiH–BF₃·Et₂O.     

Chiral Phosphine Ligands Derived fro m Sugars .14 . Crystal Structure of Diphenyl( m ethyl4’,6’-O-benzylidene-3’-deoxy-α- D-altropyranoside-3-)phosphine Oxide

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