123809-60-9

Stereochemical elucidation of molecules with multiple chiral centers is difficult. Even with VCD spectroscopy, excluding all but one diastereomeric structural candidate is challenging because the stereochemical inversion of one chiral center among many centers does not always result in noticeable differences in their VCD spectra. This work demonstrates that the introduction of a suitable VCD chromophore with absorption in the 2300-1900 cm-1 region can be used for extracting local stereochemical information and for the stereochemical assignment of the C-1 position of various sugars as a case study. Through studies on a series of epimeric pairs of monosaccharides and their derivatives, we found that the introduction of one -OCD3 group to each C-1 position produced almost mirror-image VCD patterns in the 2300-1900 cm-1 region depending on the C-1 stereochemistry irrespective of the other molecular moieties. This work also shows that comparison of the observed VCD signals and the calculated ones enables the stereochemical assignment of a chiral center in the vicinity of the chromophore. This study provides a proof of concept that the use of a VCD chromophore in the 2300-1900 cm-1 region enables the analysis of selected stereochemistry of suitable molecular systems. Further studies on this concept should lead to the development of a method useful for the structural elucidation of other types of complex molecules.

A convergent synthesis of the complex, doubly-branched pentasaccharide domain of the natural-product immunoadjuvant jujuboside A is described. The key step is a sterically-hindered glycosylation reaction between a branched trisaccharide trichloroacetimida

The fragmentation mechanisms of prototypical disaccharides have been studied herein by coupling tandem mass spectrometry (MS) with collisional chemical dynamics simulations. These calculations were performed by explicitly considering the collisions between the protonated sugar and the neutral target gas, which led to an ensemble of trajectories for each system, from which it was possible to obtain reaction products and mechanisms without pre-imposing them. The β-aminoethyl and aminopropyl derivatives of cellobiose, maltose, and gentiobiose were studied to observe differences in both the stereochemistry and the location of the glycosidic linkage. Chemical dynamics simulations of MS/MS and MS/MS/MS were used to suggest some primary and secondary fragmentation mechanisms for some experimentally observed product ions. These simulations provided some new insights into the fundamentals of the unimolecular dissociation of protonated sugars under collisional induced dissociation conditions.

Fully unprotected D-glucose, D-mannose, and D-fructose were regioselectively glycosylated with several phenylthioglycosides to afford glycosyl-β(1→6)-α/β-D-glucopyranose, glycosyl- β(1→1)-α-D-mannofuranoside, and glycosyl-β(1→1)- β-D-fructopyranose in goo

The first synthesis of leptosin, a novel glycoside isolated from mānuka honey is described. Utilising an acetyl protecting group strategy the glycoside was obtained with excellent anomeric selectivity by deploying a Schmidt glycosylation as a key step.

A simple and general synthetic protocol to obtain oligosaccharide-appended salicylaldehydes, key intermediates for the synthesis of water-soluble metal-salophen complexes, is here reported. Six new aldehydes have been prepared and fully characterized as well as the corresponding zinc- and uranyl-salophen complexes. These new derivatives show very good solubility in water. Preliminary studies on the association of compound 19-U, that is, the uranyl maltotetraose derivative, with hydrogen phosphate and fluoride provide very encouraging results and open up the possibility of using such compounds for the efficient recognition of anions in pure water.

A series of alkyl α/β-(1→6)-diglucopyranosides 1-12 were synthesized and assessed for cytotoxicity against HL-60, U937, Molt-3 and MCF-7 cancer cell lines. The menthyl derivatives displayed strong cytotoxic properties showing IC50 values betwee

Derivatization of carbohydrates is of considerable interest since the derivatives can be used for structural studies in the field of mass spectrometry. We report here the synthesis of a series of sterically crowded derivatives of various linkage and stere

Two indole glycosides, calanthoside and glucoindican, were isolated from two oriental orchids, Calanthe discolor LINDL. and C. liukiuensis SCHLTR., together with calaphenanthreol, calaliukiuenoside, and bioactive known alkaloids, tryptanthrin, indirubin, and isatin. The structures of calanthoside, glucoindican, calaphenanthreol, and calaliukiuenoside were determined on the basis of physicochemical and chemical evidence. Furthermore, it was found that enzymatic hydrolysis of calanthoside furnished tryptanthrin as the main product, whereas indirubin and isatin were obtained by acid hydrolysis of calanthoside.

We have investigated the thermotropic and lyotropic properties of some long chain alkyl glycosides with disaccharide headgroups. The thermotropism was measured with polarising microscopy and additionally the lyotropism with the contact preparation method, Fourier-transform Infrared (FTIR) spectroscopy, X-ray diffraction and small angle neutron scattering. A broad thermotropic as well as lyotropic polymorphism was found. The compounds displayed thermotropic S(A) (lamellar) and cubic phases, and the investigation of the lyotropic phase behaviour led to the observation of inverted bicontinuous cubic V(II) phases, lamellar L(α) phases, normal bicontinuous cubic V(I) phases, normal columnar H(I) phases, normal discontinuous cubic I(I) phases and lyotropic cholesteric phases. The phases are discussed with respect to the chemical structures that have been varied systematically to derive structure-property relationships. (C) 2000 Elsevier Science Ireland Ltd.

Synthetic methods for the preparation of per-O-acetylated, (1->6)-linked disaccharides containing either a D-galactose or a D-glucose residue at the reducing end are desribed.In these methods, 1,2,3,4-tetra-O-acetyl-β-trityl-β-D-glucopyranose was first converted into 1,2,3,4-tetra-O-acetyl-β-glucopyranose (1) by rapid treatment with 90percent triflouroacetic acid, followed by rapid isolation designed to minimize O-acyl migration.Disaccharides were formed by glucosylation of 1 or 1,2:3,4-di-O-isopropylidene-D-galactopyranose with per-O-acetylglycosyl halides.Isopropylidene groups in the resulting disaccharide, if present, were removed, and the disaccharide was per-O-acetylated.Per-O-acylated β-Gal-(1->6)-Glc and β-GlcNAc-(1->6)-Gal, and a mixture of per-O-acetylated α-Gal-(1->6)-Gal and β-Gal-(1->6)-Gal (in the ratio 3:7) were thus obtained.The per-O-acetylated Gal-(1->6)-Gal disaccharides were converted, by a reaction sequence previously reported, into (2,2-dimethoxyethyl)aminocarbonylmethyl 1-thio-β-D-glycosides, wich could then be coupled to proteins via reductive alkylation.For the anomeric mixture of per-O-acetylated Gal-(1->6)-Gal, conversion into the corresponding 1-thioglycoside permitted resolution of the isomers by chromatography on silica gel.When disaccharides, as borate complexes, were chromatographed on a column of a strong, anion-exchange resin, all of the (1->6)-linked disaccharides of neutral sugars tested (including melibiose) were eluted later than analogous disaccharides having other linkages, and also later than any neutral monosaccharides.

Several new peracetylated pyrimidine N-1 nucleosides containing one two β-D-hexopyranosyl residues have been synthesized and their physical characteristics are reported.The conformation of these nucleosides has been investigated by highresolution 13C-n.m.r. analysis after deblocking.It was poddible to distinguish between the syn and anti rotamers of 3-β-D-glucopyranosyluracyl, and to establish the favored anti conformation in solution of the nucleoside disaccharide, antibiotic anthelmycin.