Rapid synthesis of oligosaccharide moieties of globotriaosylceramide using fluorous protective group

The use of the Bfp (bisfluorous chain type propanoyl) group as a fluorous protective group made it possible to rapidly synthesize galabiose and the Gb3 oligosaccharide derivatives by a simple fluorous-organic extraction purification. The fluorous oligosaccharide synthesis using the Bfp group is an excellent strategic alternative to solid phase oligosaccharide synthesis, and removes some of the disadvantages of the solid phase method.     

Solvent interactions and conformational choice in a core N-glycan segment: gas phase conformation of the central, branching trimannose unit and its singly hydrated complex

The intrinsic conformational preferences and structures of the branched trimannoside, alpha-phenyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside (which contains the same carbohydrates found in a key subunit of the core pentasaccharide in N-glycans) and its singly hydrated complex, have been investigated in the gas phase isolated at low temperature in a molecular beam expansion. Conformational assignments of their infrared ion dip spectra, based on comparisons between experiment and ONIOM (B3LYP/6-31+G(d):HF/6-31G(d)) and single-point MP2 calculations have identified their preferred structures and relative energies. The unhydrated trimannoside populates a unique structure supported by two strong, central hydrogen bonds linking the central mannose unit (CM), and its two branches (3M and 6M) closely together, through a cooperative hydrogen-bonding network: OH4(CM)-->OH6(3M)-->OH6(6M). A closely bound structure is also retained in the singly hydrated oligosaccharide, with the water molecule bridging across the 3M and 6M branches to provide additional bonding. This structure contrasts sharply with the more open, entropically favored trimannoside structure determined in aqueous solution at 298 K. In principle this structure can be accessed from the isolated trimannoside structure by a simple conformational change, a twist about the alpha(1,3) glycosidic linkage, increasing the dihedral angle psi[C1(3M)-O3(3M)-C3(CM)-C2(CM)] from approximately 74 degrees to approximately 146 degrees to enable accommodation of a water molecule at the centrally bound site occupied by the hydroxymethyl group on the 3M ring and mediation of the water-linked hydrogen-bonded network: OH4(CM) -->OH(W)-->OH6(6M). The creation of a "water pocket" motif localized at the bisecting axis of the trimannoside is strikingly similar to the structure of more complex N-glycans in water, suggesting perhaps a general role for the "bisecting" OH4 group in the central (CM) mannose unit.     

Rossicasins A, B and rosicaside F, three new phenylpropanoid glycosides from Boschniakia rossica

Three phenylpropanoid glycosides have been isolated, together with the known phenylpropanoid glycosides rossicaside A (4), B (5), E (6), and trans-p-coumaryl alcohol 1-O-beta-D-glucopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->3)-beta-D-glucopyranoside (7), and an acylated oligosaccharide beta-D-glucopyranosyl(1-->4)-alpha-L-rhamnopyranosyl-(1-->3)-(4-O-trans-caffeoyl)-D-glucopyranose) (8), from the aqueous extract of Boschniakia rossica (CHAM. et SCHLECH.) FEDTSCH. et FLEROV. Spectroscopic evidence led to the assignments of their structures as trans-p-coumaryl-(6'-O-beta-D-xylopyranosyl)-O-beta-D-glucopyranoside (1), trans-p-coumaryl-(6'-O-alpha-L-arabinopyranosyl)-O-beta-D-glucopyranoside (2) and 2-(3,4-dihydroxyphenyl)-R,S-2-ethoxy-ethyl-O-beta-D-glucopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->3)(4-O-trans-caffeoyl)-beta-D-glucopyranoside (3), designated as rossicasin A, rossicasin B, and rossicaside F, respectively. Compound 7 was identified from the degradation reaction and this is the first isolation from a natural source.     

Using non-covalent complexes to direct the fragmentation of glycosidic bonds in the gas phase

An investigation of the gas phase chemistry of proton bound oligosaccharide (S)-ligand (L) non-covalent complexes, [S + H + L](+) has been carried out using electrospray ionization (ESI) and tandem mass spectrometry in a quadrupole ion trap. When subjected to collision-induced dissociation (CID), these [S + H + L](+) complexes undergo a range of reactions that can be broadly classified into three main types: (1) Simple dissociation into the individual monomers; (2) cleavage of the oligosaccharide to form B-type sequence ions; (3) cleavage of the ligand species. The second type of reaction is particularly interesting as it can produce a "ladder series" of [B(x) + L](+) ions via ligand induced oligosaccharide bond cleavage. This novel gas phase reaction greatly simplifies the sequencing of oligosaccharides. Both the oligosaccharide and ligand were found to influence the type of reaction pathway observed, with the "ladder series" of [B(x) + L](+) ions being favored for permethylated oligosaccharides and for bifunctional ligands. Cytosine is a particularly good ligand at facilitating the formation of [B(x) + L](+) ions. Analogies with condensed phase chemistry of sugars is made and a potential mechanism for ligand induced oligosaccharide bond cleavage is proposed.     

A new phenoxyacetate-based linker system for the solid-phase synthesis of oligosaccharides

[structure: see text]. A novel linker system has been designed, and its first application to solid-phase oligosaccharide synthesis is described. The use of the highly reactive o-nitro-phenoxyacetate linker allows a fast and quantitative cleavage using mild basic conditions. This method combined with the trichloroacetimidate glycosylation exhibits highly promising results as demonstrated for the synthesis of tetrasaccharide 1 (n = 3) containing glucose beta(1 --> 4) and beta(1 --> 6) linkages.     

Multistability in a BEDT-TTF based molecular conductor

The low dimensional organic conductor (BEDT-TTF)(2)Br(1.3)I(1.1)Cl(0.6) [BEDT-TTF = bis(ethylenedithio)tertathiafulvalene] is shown to be a unique molecular solid that exists in three crystalline polymorphic forms (alpha'-, alpha' "-, beta' '-phase) and, surprisingly, is able to adopt the same metal-like beta' '-phase at both low (T < 185 K) and high (T > 395 K) temperatures. Several crystals of the alpha'- and alpha' "-phases have been studied using three different techniques: dc-conductivity measurements, ESR spectroscopy, and X-ray diffraction analysis. All these techniques show the existence of the reversible semiconductor <--> metal (alpha' " <--> beta' ') phase transition at both high and low temperatures as well as the alpha' <--> alpha' " phase transition at high temperatures. The phase transitions of these polymorphs are characterized by huge hysteresis and dramatic changes in the transport and magnetic properties. Based on ab initio calculations, it is suggested that dipole-dipole interactions can play a key role in the rich polymorphism of this molecular solid.     

Chemoenzymatic synthesis of sialylated glycopeptides derived from mucins and T-cell stimulating peptides.

The Tn, T, sialyl-Tn, and 2,3-sialyl-T antigens are tumor-associated carbohydrate antigens expressed on mucins in epithelial cancers, such as those affecting the breast, ovary, stomach, and colon. Glycopeptides carrying these antigens are of interest for development of cancer vaccines and a short, chemoenzymatic strategy for their synthesis is reported. Building blocks corresponding to the Tn (GalNAc alpha-Ser/Thr) and T [Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens, which are relatively easy to obtain by chemical synthesis, were prepared and then used in the synthesis of glycopeptides on the solid phase. Introduction of sialic acid to give the sialyl-Tn [Neu5Ac alpha(2-->6)GalNAc alpha-Ser/Thr] and 2,3-sialyl-T [Neu5Ac alpha(2-->3)Gal beta(1-->3)GalNAc alpha-Ser/Thr] antigens is difficult when performed chemically at the building block level. Sialylation was therefore carried out with recombinant sialyltransferases in solution after cleavage of the Tn and T glycopeptides from the solid phase. In the same manner, the core 2 trisaccharide [Gal beta 1-->3(GlcNAc beta 1-->6)GalNAc] was incorporated in glycopeptides containing the T antigen by using a recombinant N-acetylglucosaminyltransferase. The outlined chemoenzymatic approach was applied to glycopeptides from the tandem repeat domain of the mucin MUC1, as well as to neoglycosylated derivatives of a T cell stimulating viral peptide.     

Observed bands in Raman and infrared spectra of 1,3-dioxolane and their assignments

We present a Raman study of liquid and polycrystalline dioxolane, together with data for a solid dioxolane/argon film. Observed bands are assigned to the bent conformer on the basis of ab initio calculated vibrations, accompanied with potential energy distribution. Two internal modes were calculated at 658 and 720 cm⁻¹ for the bent form. These were observed at 665 and 722 cm⁻¹ in liquid, and split into four bands (at 694, 697, 725, and 728 cm⁻¹) in the crystal at 10 K. In the solid dioxolane/argon film an additional band appears at 705 cm⁻¹ (between the bands at 675 and 726 cm⁻¹). A search for an additional dioxolane conformer trapped in argon was undertaken by performing molecular dynamics simulations of dioxolane/argon solid film and averaging overall molecular conformations. The resulting conformation did not correspond to an energy minimum, but indicated that changes of only a few degrees in dihedral angles could shift ring deformation and OCO bending modes for more than 10 cm⁻¹. Differential scanning calorimetric measurements gave evidence of solidification upon cooling at 146 K, and two phase changes on heating (one at 158.3 K, and a melting transition at 180.3 K). Further study is required on the hysteresis effect in the temperature behavior of dioxolane, and on the nature of the intermediate solid phase.     

Chemical constituents from Pseudolarix kaempferi

A novel degraded triterpenoid isopseudolaritone A (1) and one new oligosaccharide, 1-O-isopropyl-6-O-[2-O-methyl-alpha-L-rhamnopyranosyl(1 --> 6)]-beta-D-glucopyranose (2), two new artefacts, 9-O-formacyl cedrusin (5) and 9,9'-O-diformacyl cedrusin (6), as well as 12 known phenolic Compounds (3-4, 7 16), were isolated from the root bark of Pseudolarix kaempferi. Their structures were elucidated mainly by spectroscopic methods.     

The 2-naphthylmethyl (NAP) group in carbohydrate synthesis: first total synthesis of the GlyCAM-1 oligosaccharide structures

Total syntheses of the GlyCAM-1 (glycosylation-dependent cell adhesion molecule-1) oligosaccharide structures: [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-(6-O-SO3Na)-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (1) and [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (2) through a novel sialyl LewisX tetrasaccharide donor are described. Employing sequential glycosylation strategy, the starting trisaccharide was regio- and stereoselectively constructed through coupling of a disaccharide imidate with the monosaccharide acceptor phenyl-6-O-naphthylmethyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside with TMSOTf as a catalyst without affecting the SPh group. The novel sialyl Lewisx tetrasaccharide donor 3 was then obtained by alpha-L-fucosylation of trisaccharide acceptor with the 2,3,4-tri-O-benzyl-1-thio-beta-L-fucoside donor. The structure of the novel sialyl Lewisx tetrasaccharide was established by a combination of 2D DQF-COSY and 2D ROESY experiments. Target oligosaccharides 1 and 2 were eventually constructed through heptasaccharide which was obtained by regioselective assembly of advanced sialyl Lewisx tetrasaccharide donor 3 and a sialylated trisaccharide acceptor in a predictable and controlled manner. Finally, target heptasaccharides 1 and 2 were fully characterized by 2D DQF-COSY, 2D ROESY, HSQC, HMBC experiments and FAB mass spectroscopy.     

Synthesis and thermal energy storage properties of the polyurethane solid–solid phase change materials with a novel tetrahydroxy compound

Based on the phase change theory, a novel tetrahydroxy compound (THCD) was designed and prepared. Depending on the spatial structure of the tetrahydroxy compound, a form-stable thermoplastic polyurethane solid–solid phase change material (TPUPCM) was synthesized via employing PEG as soft segments, while multi-benzene ring structure made by 4,4′-diphenylmethane diisocyanate and tetrahydroxy compound as hard segments. The composition and structure of THCD and TPUPCM, the TPUPCM’s the weight average molecular weight and number average molecular weight, dissolving and melting abilities, phase change behaviors, thermal performances and crystalline morphology were investigated by Fourier transform infrared spectrometer, ¹H nuclear magnetic resonance spectrometer, multiangle laser light scattering apparatus, differential scanning calorimentry, dynamic mechanical thermal analysis, thermogravimetry analysis system, wide-angle X-ray diffraction, polarizing optical microscopy. The results show that the solid–solid phase change material owns excellent phase change properties and a broad processing temperature range. The heating cycle phase change enthalpy is 137.4 J/g, and the cooling cycle phase change enthalpy is 127.6 J/g. The started decomposition temperature and the maximum decomposition temperature are at 323.5 and 396.2 °C, respectively. Furthermore, the solid–solid phase change material is dissolvable, meltable and can be processed directly, and has great potential applications in thermal energy storage.     

Chiral self-assembly of enantiomerically pure (4S,7R)-campho[2,3-c]pyrazole in the solid state: a vibrational circular dichroism (VCD) and computational study

NH-Indazoles in solid phase usually form NH⋯N hydrogen bonds between positions 1 and 2, which determine the secondary structure, forming dimers, trimers, or catemers (chains). Thus, the difficulty of the experimental analysis of the structure of the family of 1H-indazoles is clear. We have outlined a complete strategy by using different techniques of vibrational spectroscopy that are sensitive (VCD) and not sensitive (IR, FarIR, and Raman) to the chirality together with quantum chemical calculations. We have studied the chiral structure of (4S,7R)-campho[2,3-c]pyrazole both in solution (CCl₄) and in the solid phase (crystal). This compound crystallizes as a chiral trimer (LABHEB), with the monomer also being chiral. Herein, Far-IR, IR, and Raman spectra in solution and in the solid state are assigned using the support of B3LYP/6-31G(d) and B97D/6-31+G(d,p) calculations of (4S,7R)-campho[2,3-c]pyrazole monomers, dimers, and trimers, these last cyclamers being partially and fully optimized. Later, analysis of the vibrational circular dichroism (VCD) spectra allowed us to determine the chiral self-assembly of (4S,7R)-campho[2,3-c]pyrazole crystals (LABHEB). In the crystal, only the trimers are present while in solution, the monomer predominates. We have highlighted the importance of the analysis of the low frequency region (700–25 cm⁻¹) in the FT-Raman and Far-IR spectra, because it provides relevant information in order to confirm the presence of the trimers in the solid phase.     

Standard enthalpies of formation of 2-aminobenzothiazoles in the crystalline phase by rotating-bomb combustion calorimetry

The standard molar enthalpies of combustion of 2-aminobenzothiazole (2AB), 2-amino-4-methyl-benzothiazole (2A4MB), and 2-amino-6-methyl-benzothiazole (2A6MB) were determined in the crystalline phase at T = 298.15 K using a rotating-bomb combustion calorimeter. The molar energies of combustion of these compounds were found to be: (−4273.6 ± 0.9), (−4896.9 ± 1.1), and (−4906.9 ± 1.2) kJ · mol⁻¹, respectively. From these values, the corresponding standard molar enthalpies of formation in the solid phase were obtained as: (59.55 ± 1.28), (2.71 ± 1.50), and (13.53 ± 1.53) kJ · mol⁻¹, respectively. The enthalpies of formation in the gas phase were determined using the experimental enthalpies of formation in the solid phase and predicted values of the enthalpies of sublimation. Additionally, the enthalpies of formation in the gas phase were calculated by means of the Gausian-4 theory, using several gas-phase working reactions, and were compared with those found using the predicted enthalpies of sublimation.     

A new class of proton-conducting ionic plastic crystals based on organic cations and dihydrogen phosphate

Choline dihydrogen phosphate ([N_1.1.1.2OH]DHP) and 1-butyl-3-methylimidazolium dihydrogen phosphate ([C₄mim]DHP) were synthesized as a new class of proton-conducting ionic plastic crystals. Both [N_1.1.1.2OH]DHP and [C₄mim]DHP showed solid–solid phase transition(s) and showed a final entropy of fusion lower than 20 J K⁻¹ mol⁻¹ which is consistent with Timmerman’s criterion for molecular plastic crystals. The ionic conductivity of [N_1.1.1.2OH]DHP was in the range of 10⁻⁶ S cm⁻¹–10⁻³ S cm⁻¹ in the plastic crystalline phase. On the other hand, the ionic conductivity of [C₄mim]DHP showed about 10⁻⁵ S cm⁻¹ in the plastic crystalline phase. [N_1.1.1.2OH]DHP showed one order of magnitude higher ionic conductivity than [C₄mim]DHP in the temperature range where the plastic phase is stable.     

Synthesis of fragments of the glycocalyx glycan of the parasite Schistosoma mansoni

The chemical synthesis of alpha-L-Fucp-(1 --> 3)-beta-D-GalpNAc-(1 --> 4)-beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2, beta-D-GalpNAc-(1 --> 4)-[alpha-L-Fucp-(1 --> 3)-]beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2, and alpha-L-Fucp-(1 --> 3)-beta-D-GalpNAc-(1 --> 4)-[alpha-L-Fucp-(1 --> 3)-]beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2 is described. These structures represent fucosylated oligosaccharide fragments of the glycocalyx glycan of the cercarial stage of the parasite Schistosoma mansoni, and in protein-conjugated form they are potential diagnostics in the search for antibodies raised against the glycan in the serum of infected humans.     

Expression, purification, and characterization of a galactofuranosyltransferase involved in Mycobacterium tuberculosis arabinogalactan biosynthesis

The major structural component of the cell wall of Mycobacterium tuberculosis is a lipidated polysaccharide, the mycoyl-arabinogalactan-peptidoglycan (mAGP) complex. This glycoconjugate plays a key role in the survival of the organism, and thus, enzymes involved in its biosynthesis have attracted attention as sites for drug action. At the core of the mAGP is a galactan composed of D-galactofuranose residues attached via alternating beta-(1-->5) and beta-(1-->6) linkages. A single enzyme, glfT, has been shown to synthesize both glycosidic linkages. We report here the first high-level expression and purification of glfT by expression of the Rv3808c gene in Escherichia coli C41(DE3). Following a three-step purification procedure, 3-7 mg of protein of >95% purity was isolated from each liter of culture. We subsequently probed the substrate specificity of glfT by evaluating a panel of potential mono- and oligosaccharide substrates and demonstrated, for the first time, that trisaccharides are better substrates than disaccharides and that one disaccharide, in which the terminal D-galactofuranose residue is replaced with an L-arabinofuranose moiety, is a weak substrate. Kinetic characterization of the enzyme using four of the oligosaccharide acceptors gave K(m) values ranging from 204 microM to 1.7 mM. Through the use of NMR spectroscopy and mass spectrometry, we demonstrated that this recombinant enzyme, like the wild-type protein, is bifunctional and can synthesize both beta-(1-->6) and beta-(1-->5)-linkages in an alternating fashion. Access to purified glfT is expected to facilitate the development of high-throughput assays for the identification of inhibitors of the enzyme, which are potential antituberculosis agents.