Stereoselective synthesis of polyoxygenated linear diaza-triquinanes via intramolecular 1,3-dipolar cycloaddition of sugar-derived hex-5-enals

An efficient and stereoselective synthesis of diaza-triquinanes, the skeleton structures of many natural products, has been accomplished by intramolecular 1,3-dipolar cycloaddition of azomethine imine generated from sugar-derived hex-5-enal and pyrazolidin-3-one.     

Spiro-sulfamidate and sulfate nucleosides via 2′ and 3′-C-branched-chain sugars and nucleosides

C-branched-chain sugars and nucleosides were obtained by organocatalysis from ulose derivatives. After a reduction step, the corresponding 1,3-diol was derivatized into 3′-spiro-sulfamidates and unexpected sulfates by treatment with a Burgess reagent. Deprotection of the Boc-derivatives was carried out while preserving the cyclic sulfate. An example of ring opening of the cyclic sulfate derivative with sodium azide leading to the corresponding 3′-C-azidoalkyl branched-chain nucleosides is given.     

Chiron approach strategy to the bicyclic oxazolidinylpiperidine: a building block for preparing mono- and bi-cyclic iminosugars

A chiron approach to the synthesis of bicyclic oxazolidinylpiperidine, a synthetically potential building block for preparing mono- and bi-cyclic iminosugars, is reported from d-glucose using ring closing metathesis as the key step.     

Substituent effects in endocyclic cleavage-recyclization anomerization reaction of pyranosides

Pyranosides with 2,3-trans carbamate or 2,3-trans carbonate groups are anomerized under mild acidic conditions via endocyclic cleavage reaction. In order to understand the nature of the anomerization reaction via the endocyclic cleavage-recyclization process, the substituent effects at various positions were investigated.     

Synthesis and characterisation of a chiral lanthanoid cluster with an unusually exposed cubane core via concomitant deesterification of ethyl acetate

An unusual chiral lanthanoid cluster has been synthesised and characterised that exhibits a cubane cage motif with a remarkably exposed central core. This discovery stems from the use of a new asymmetric diketone ligand, (Z)-3-hydroxy-3-methyl-1-(1,2:3,4-di-O-isopropylidene-α-d-galactopyranose)prop-2-en-1-one (Hmgp), which incorporates both a methyl terminus and a protected d-galactose moiety to induce chirality. Reaction of this ligand with hydrated holmium chloride results in the formation of a cubane cluster, [Ho₄(μ₃-OH)₄(η²-mgp)₆(μ-η²-mgp)(μ-η²-Ac)(H₂O)₂] (1), which bears seven chiral ligands that form a highly shielded hemisphere and an acetate co-ligand that is postulated to form via deesterification of ethyl acetate.     

Hydration forces between bilayers in the presence of dissolved or surface-linked sugars

We analyse the experimental evidence of the hydration force near phospholipid bilayers when the “solvent” is a solution of carbohydrates. Two cases must be clearly distinguished: when sugar is dissolved, depletion causes a supplementary attractive force, while in the case of sugar linked to the lipid the contact pressure increases by orders of magnitude. Attractive interaction inferred between bilayers is sometimes derived from indirect evidence, i.e. scattering, attraction between layers adsorbed, shape of phase boundary limits, and without the simultaneous determination of the osmotic compressibility. Generally, water molecules in the first hydration shell of sugar compete with water molecules bound (by more than one kT in free energy) to lipid head-groups. A general result is that the decay length of any repulsive effect remains close to 0.2 nm, even in concentrated sugar solutions. A tentative general explanation of this experimental fact is given together with consequences, such as the possibility of several types of critical points appearing in bilayer stacks. Decay length as well as effective contact pressure is considered with respect to carbohydrate activity.     

A sorbitol-selective fluorescence sensor

A new anthracene derivative bearing two phenylboronic acid groups at the 1,8-positions was prepared and its binding properties towards sorbitol, xylitol, fructose, glucose and galactose have been studied using fluorescence analysis.     

Structural insights of a cellobiose dehydrogenase enzyme from the basidiomycetes fungus Termitomyces clypeatus

Filamentous fungi secrete various oxidative enzymes to degrade the glycosidic bonds of polysaccharides. Cellobiose dehydrogenase (CDH) (E.C.1.1.99.18) is one of the important lignocellulose degrading enzymes produced by various filamentous fungi. It contains two stereo specific ligand binding domains, cytochrome and dehydrogenase - one for heme and the other for flavin adenine dinucleotide (FAD) respectively. The enzyme is of commercial importance for its use in amperometric biosensor, biofuel production, lactose determination in food, bioremediation etc. Termitomyces clypeatus, an edible fungus belonging to the basidiomycetes group, is a good producer of CDH. In this paper we have analyzed the structural properties of this enzyme from T. clypeatus and identified a distinct carbohydrate binding module (CBM) which is not present in most fungi belonging to the basidiomycetes group. In addition, the dehydrogenase domain of T. clypeatus CDH exhibited the absence of cellulose binding residues which is in contrast to the dehydrogenase domains of CDH of other basidiomycetes. Sequence analysis of cytochrome domain showed that the important residues of this domain were conserved like in other fungal CDHs. Phylogenetic tree, constructed using basidiomycetes and ascomycetes CDH sequences, has shown that very surprisingly the CDH from T. clypeatus, which is classified as a basidiomycetes fungus, is clustered with the ascomycetes group. A homology model of this protein has been constructed using the CDH enzyme of ascomycetes fungus Myricoccum thermophilum as a template since it has been found to be the best match sequence with T. clypeatus CDH. We also have modelled the protein with its substrate, cellobiose, which has helped us to identify the substrate interacting residues (L354, P606, T629, R631, Y649, N732, H733 and N781) localized within its dehydrogenase domain. Our computational investigation revealed for the first time the presence of all three domains - cytochrome, dehydrogenase and CBM - in the CDH of T. clypeatus, a basidiomycetes fungus. In addition to discovering the unique structural attributes of this enzyme from T. clypeatus, our study also discusses the possible phylogenetic status of this fungus.     

Synthesis and Properties of New Tricephalic Tetrasiloxane Surfactants Containing Carbohydrate and Hydrocarbon Chain

A new family of tricephalic tetrasiloxane surfactants containing carbohydrate and hydrocarbon chain (SiC(n + 1)N-GA, in which n + 1 represents a hydrocarbon chain length of 1, 8, 12, 16), was synthesized using two-step method. Their structures were confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (¹H NMR). Their surface activities and aggregation properties in aqueous solution were investigated by surface tension measurements, transmission electron microscopy, and dynamic light scattering. The results indicated that the critical micelle concentration (CMC) of these surfactants increased and the surface tension (γ_CMC) at the CMC decreased with an increase in the number of hydrocarbon chain, and they can self-assemble into spherical micelles with average diameters in the range from 5 to 200 nm, which are smaller than for single-headed surfactants.     

Selective deprotection of trityl group on carbohydrate by microflow reaction inhibiting migration of acetyl group

The trityl group is an important and useful protecting group for primary hydroxy groups on carbohydrates. However, during deprotection, neighboring acetyl groups can easily migrate to the deprotected hydroxy groups. Hence, deprotection of trityl groups was optimized using a microreactor with regard to flow rate, reagent concentration, reaction time, and substrate concentration. The optimized microflow reaction conditions inhibited migration and could be applied to large-scale reactions and other substrates.