摘要:

A novel density functional method is presented for the calculation of electronic and thermodynamical properties of oligosaccharides. This method, termed K2-BVWN, offers two advantages; it scales asN3, whereNis the number of basis functions, and there are only two adjustable parameters. The current density functional method is tested in terms of reproducing high level gas phaseab initiocalculations in eleven low energy conformers of D-glucopyranose including exo-anomeric and different hydroxymethyl orientations (G−,G+, andT). The K2-BVWN method is also tested in terms of reproducing the spectroscopic features of D-glucopyranose and D-mannopyranose (α/β) as compared with both a vibrational self-consistent field calculation (VSCF) as well as experimental infrared spectroscopy. The VSCF calculations offer the advantage that it is possible to include higher order mode coupling and anharmonic effects directly into the calculation of the vibrational frequencies. In general, the K2-BVWN method reproduces theab initioenergetic trends of the different conformers of D-glucose. While the absolute energies are not the same between theab initioand the K2-BVWN method, both methods do predict a preference for the α-anomer in the gas phase (0.4 kcal/molab initio, 0.0 – 0.5 kcal/mol K2-BVWN). The K2-BVWN method was able to reproduce the experimental and VSCF calculated spectrum of both D-glucopyranose and D-mannopyranose in the frequency range between 1500 – 800 cm−1. Because the current density functional method is both relatively quick and accurate, it represents a significant advancement in the development of oligosaccharide force fields.

ISSN:0732-8303    

DOI:10.1080/07328309908544041

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The conformational behaviour of the major trisaccharide repeating unit (α-D-Galp-(1→2)-β-D-Ribf-(1→9)-α-5-O-Me-Kdnp-) of the polysaccharide fromSinorhizobium frediiSVQ293, a mutant derivative has been analysed by NMR spectroscopy and extensive molecular dynamics simulations. The results obtained indicate that the five-membered ring adopts an almost unique conformation as do the pyranose rings. The Ribf-(1→9)-α-5-O-Me-Kdnplinkage may adopt a variety of conformations while the α-D-Galp-(1→2)-β-D-Ribf- also populates an extended surface of the Φ/Ψ map. Two 10 ns MD simulations using the GB/SA continuum solvent model for water and the MM3* force field provides a population distribution of conformers which satisfactorily agrees with the experimental NMR data for both the glycosidic linkages and the hydroxymethyl groups.

ISSN:0732-8303    

DOI:10.1080/07328309908544042

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Miniature crystal models of six small carbohydrates were examined using the PM3 semiempirical quantum mechanics method. The minicrystal structures, consisting of 27 sugar residues, were optimized by the combined procedure of partial optimization and reconstruction of the model, while maintaining the original crystal symmetries. All of the minicrystals were successfully optimized without exhibiting a great increase in an energy at any reconstruction step. Some minicrystals showed a prolonged behavior of optimization cycles. A major source of structure change appeared to arise from hydroxyl group rotations wherein the largest movements mostly occurred in an early optimization stage. No significant deformations in geometry of either residues or hydrogen bonds were observed in the final minicrystal structures. The thermodynamic values calculated for the optimized minicrystals were in reasonably good agreement with the literature data. The present study indicated that the PM3 semiempirical method successfully predicted the basic features of intermolecular hydrogen bonding involved in a condensed system.

ISSN:0732-8303    

DOI:10.1080/07328309908544043

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

3-Methyl-1-phenyl-2-phospholene and 1-phenyl-2-phospholene 1-oxides were converted into 2-bromo-3-hydroxy-3-methyl-1-phenylphospholane and 2-bromo-3-hydroxy-1-phenylphospholane 1-oxide (1-bromo-1,3,4-trideoxy-1,4-C-[(R, S)-phenylphosphinylidene]-glycero-tetrofuranose) by the action of bromine in aqueous medium. The bromo substituent of the phospholane was substituted by treatment with amines or an azide anion to afford novel glycoside derivatives of phosphanyl sugar analogs such as 2-amino-3-hydroxy-1-phenylphospholane (3,4-dideoxy-1,4-C-[(R, S)-phenylphosphinylidene]-glycero-tetrofuranosylamine) and 2-azido-3-hydroxy-3-methyl-1-phenylphospholane 1-oxides with retention of the configuration. The 1,3-dipolar cycloaddition of the 2-azido derivative of the phospholane with alkynes gave 3-hydroxy-3-methyl-1-phenyl-2-(triazol-1′-y1)phospholane 1-oxides as a novel triazole-derived nucleoside of phosphanyl sugar analogs. The structure of the glycoside and nucleoside derivatives of the phosphanyl sugar analogs prepared was deterimined from IR, NMR, and X-ray crystallography analysis.

ISSN:0732-8303    

DOI:10.1080/07328309908544044

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The synthesis of thioglycosides for use as metabolically stable biological probes is an area of continued interest. This paper describes the synthesis of functionalised carbohydrates which contain an anomeric thio group. During the course of this work we have examined the most viable route into compounds such as the specifically functionalised carbohydrates36and37, and have also investigated the usefulness of disulfides as protecting groups for anomeric thiols.

ISSN:0732-8303    

DOI:10.1080/07328309908544045

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Reaction of sugar derived phosphonates [Sug-C(O)CH2P(O)(OMe)2] with sugar aldehydes (Sug'-CHO) provides the higher enones of the general formula Sug-C(O)CH=CH-Sug' with thetransconfiguration of the double bond. The phosphonate method is superior to the previously used phosphorane methodology [Sug-C(O)CH=PPh3+ Sug'-CHO] since sugar phosphonates can be prepared in much higher yields and are much more nucleophilic than corresponding phosphoranes. The sugar enones are reduced to appropriate allylic alcohols with zinc borohydride; the stereoselectivity of this process is >97:3 (with the D-glyceroisomer predominating) when the carbonyl group is placed at the α-position to the sugar ring. CD spectroscopy was used for the determination of the configuration of higher sugar allylic alcohols.

ISSN:0732-8303    

DOI:10.1080/07328309908544046

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

p-Nitrophenyl β-chitobioside (2) was prepared fromp-nitrophenyl 2-acetamido-2--deoxy-β-D-glucopyranoside (1) using β-N-acetylhexosaminidase fromAspergillus oryzae. As minor by-product a (1→6)-linked regioisomer (3a) was formed. Addition of (NH4)2SO4and organic co-solvents (acetonitrile, dioxane) substantially increased the yield.

ISSN:0732-8303    

DOI:10.1080/07328309908544047

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

As carbohydrate probes to investigate the biological activity of novel phosphocholine-containing glycoglycerolipids ofM. fermentans, artificial glycoconjugate polymers carrying 6-O-phosphocholine α-D-glucopyranoside were synthesized. The synthesis involved α-selective 1-O-p-nitrophenylation (pNP) of 1,6-di-O-acetyl-2,3,4-tri-O-benzyl-D-glucopyranose in the presence of a Lewis acid followed by the introduction of a phosphocholine group at positionO-6 by an amidite method. ThepNP group was converted into ap-N-methacrylamidophenyl group for subsequent radical polymerization.

ISSN:0732-8303    

DOI:10.1080/07328309908544048

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Pyranose 2-oxidase, a homotetrameric FAD-flavoprotein from the fungusTrametes multicolor, catalyzes the oxidation of 1→6 disaccharides gentiobiose (β-D-Glcp-(1→6)-D-Glc), melibiose (α-D-Galp-(1→6)-D-Glc), and isomaltose (α-D-Glcp-(1→6)-D-Glc) at C-2 of their reducing moiety. The products were identified as their hydrazone derivatives.

ISSN:0732-8303    

DOI:10.1080/07328309908544049

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A derivative of an α-galactosyl trisaccharide xenoactive antigen, (2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl)-(1→3)-(2,4,6-tri-O-acetyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-acetyl-β-D-glucopyranosyl azide (5), was synthesized on a large scale (50 gram). The synthesis involved a high yielding and highly stereoselective (α/β>20:1) glycosylation reaction utilizing a thiogalactoside as the donor and a selectively protected lactose azide as the acceptor. This derivative serves as a versatile intermediate that can be transformed into a variety of α-Gal containing glycoconjugates highly desired in xenotransplantation research and pharmaceutical development.

ISSN:0732-8303    

DOI:10.1080/07328309908544050

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor