A force field for monosaccharides and (1 → 4) linked polysaccharides

A force field for monosaccharides that can be extended to (1 → 4) linked polysaccharides has been developed for the AMBER potential function. The resulting force field is consistent with the existing AMBER force field for proteins and nucleic acids. Modifications to the standard AMBER OH force constant and to the Lennard-Jones parameters were made. Furthermore, a 10–12 nonbonded term was included between the hydroxyl hydrogen of the saccharide and the water oxygen (TIP3P, SPC/E, etc.) to reproduce better the water–saccharide intermolecular distances. STO-3G electrostatic potential (ESP) charges were used to represent the electrostatic interactions between the saccharide and its surrounding environment. To obtain charges for polysaccharides, a scheme was developed to piece together saccharide residues through 1 → 4 connections while still retaining a net neutral charge on the molecule as a whole. Free energy perturbation (FEP) simulations of D -glucose and D -mannose in water were performed to test the resulting force field. The FEP simulations demonstrate that AMBER overestimates intramolecular interaction energies, suggesting that further improvements are needed in this part of the force field. To test further the reliability of the parameters, a molecular dynamics (MD) simulation of α-D -glucose in water was also performed. The MD simulation was able to produce structural and conformational results that are in accord with experimental evidence and previous theoretical results. Finally, a relaxed conformational map of β-maltose was assembled and it was found that the present force field is consistent with available theoretical and experimental results. © 1994 by John Wiley & Sons, Inc.     

Synthesis of Analogues of the Antitumor （1→6）-Branched （1→3）-Glucohexaose

β-D-Glcp-(1→）3-[β-D-Glcp-(1→6)-]α-D-Manp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp(1→6)-]D-Glcp(18)and β-D-Glcp(1→3)-[β-D-Glcp(1→6)-]α-D-Manp-(1→3)-β-D-Glcp(1→3)-[β-D-Glcp(1→6)-]β-D-Glcp-D-(1→3)-Glcp-1→OM3(29)were synthesized as the analogues of the immunomodulator β-D-Glcp-(1→3)-[β-D-Glcp(1→6)-]α-D-Glcp(1→3)-β-D-Glcp(1→63)-[β-D-Glcp(1→6)-]D-Glcp through coupling of trisaccharide donors 9 with trisaccharide acceptor 16 and tetrasaccharide acceptor 27 followed by deprotection,respectively.     

Practical and scalable synthesis of alpha-(1-->4)-linked polysaccharides composed of 6-O-methyl-D-glucose

A second-generation synthesis of synthetic 6-O-methyl-D-glucose-containing polysaccharides (sMGPs) is reported. Glycosidation acceptor A and donor B are prepared from alpha-, beta-, and gamma-cyclodextrins in high yields. The glycosidation of A and B, followed by deprotection, furnishes sMGP 12-, 14-, and 16-mers. This synthesis has appealing features such as scalability, operational simplicity, and high overall yield.     

Highly stereoselective and iterative synthesis of alpha-(1-->4)-linked polysaccharides composed of 3-O-methyl-D-mannose

A second-generation synthesis of synthetic 3-O-methyl-D-mannose-containing polysaccharides (sMMPs) is reported. The glycosidation of donor B and acceptor C, prepared from a common precursor A in two and one steps, respectively, is effected by t-butyldimethylsilyl trifluoromethanesulfonate to furnish only the desired alpha-anomer D in high yields. Unlike the first-generation synthesis, this synthesis gives the desired product free from contamination of scrambling products. A three-step protocol is used to deprotect D to furnish sMMPs.     

Molybdän(VI)-fluorid-pentafluorotellurate(VI) und Molybdän(VI)-oxid-fluorid-pentafluorotellurate(VI): MoFn(OTeF5)6−n und MoOFn(OTeF5)4−n

Molybdenum(VI)fluoride-pentafluorotellurates(VI) and Molybdenum(VI)oxide-fluoridepentafluorotellurates(VI): MoF_n(OTeF₅)_6?n and MoOF_n(OTeF₅)_4?n In MoF₆ fluorine can be replaced by F₅TeO-groups by means of B(OTeF₅)₃. Rearrangement reactions and internal fluorination finally leads to MoF_n(OTeF₅)_6?n and MoOF_n(OTeF₅)_4?n.     

Ceric-ion-initiated grafting of methyl methacrylate onto (1 → 5)-α-D-ribofuranan and (1 → 5)-α-D-xylofuranan

We report herein studies of grafting of MMA onto (1 → 5)-α-D -ribofuranan and (1 → 5)-α-D -xylofuranan by ceric ion initiation both in water and in dimethyl sulfoxide (DMSO). In aqueous medium, the graft polymer having high grafting (%) can be obtained easily without adding any nitric acid. The degradation of polysaccharide by the acidic ceric ion solution is not serious; 73–82% of its original molecular weight remained after the polymerization. In DMSO, graft polymers having lower grafting (%) and lower molecular weight of grafts were obtained.     

Synthesis of (1-->4)-linked 2-deoxy-2-fluoroglucose oligomers. 1

[reaction: see text] Thioglycosides of natural monosaccharides are readily converted into their corresponding chlorides by diphenylchlorosulfonium chloride. This reagent can likewise effect the conversion of the more stable 4-chlorophenylthio 2-deoxy-2-fluoroglucose derivatives into chloride glycosyl donors. On the basis of this activation strategy, it was possible to assemble unnatural oligosaccharides composed of 2-fluorodeoxy sugars.     

Solid-phase synthesis of a naturally occurring β-(1→5)-linked d-galactofuranosyl heptamer containing the artificial linkage arm L-homoserine

The glycosyl donor 2,3-di-O-benzoyl-5-O-levulinoyl-6-O-pivaloyl-β-D-Galactofuranosyl chloride and properly-protected L-homoserine covalently bound to polystyrene were employed for the stereoregular formation of a D-galactofuranosyl heptamer containing β-(1→)-interglycosidic bonds and a β-linked L-homoserine a solid-phase approach     

Configurational statistics of poly(ethylene terephthalate) chains

The length of the span of the terephthaloyl residue in poly(ethylene terephthalate) guarantees independence of the conformations of successive repeating units of the chain. Interactions within units of the chain are amenable to interpretation by comparisons with related polymers; cis and trans conformations of the terephthaloyl residue are given equal weighting. The mean-square dimension ratio (〈r²〉₀/M)_∞ estimated on this basis is in substantial accord with the value deduced from experiments.     

α-D-Glycosyl-Substituted α,α-D-Trehaloses with (1 → 4)-Linkage: Syntheses and NMR Investigations

Two symmetrical trehalose glycosyl ‘acceptors’ 4 and 6 were prepared and three of the unsymmetrical type, 8 , 10 , and 11 . Glucosylation of symmetrical ‘acceptor’ 4 gave a higher yield of trisaccharide (44%) than protect ve-group manipulation, namely via selective debenzylidenation 2 → 9 or monoacetylation 2 → 5 which proceeded in moderate yields (33–34%). A comparison of catalysts in the cis-glucosylation of trehalose ‘acceptor’ 10 with tetra-O-benzyl-β-D -glucopyranosyl fluoride 13 profiled triflic anhydride ((Tf)₂O) as a new reactive promoter yielding 92% of trisaccharide 14 , deblocking gave the target saccharide α-D -glucopyranosyI-( 1 → 4 )-α,α-D -trehalose. ¹H-NMR spectra of most compounds were analyzed extensively. The use of the ID TOCSY technique is advocated for its time efficiency, if needed supplemented by ROESY experiments.     

3-Azawurtzitan und 3(4 → 5)abeo-3-Azawurtzitan

3-Azawurtzitane and 3(4 → 5)abeo-3-Azawurtzitane 3-Azawurtzitane (14) and 3(4 → 5)abeo-3-azawurtzitane (15) as well as derivatives thereof are described. The known tricyclic unsaturated ketone 1 was transformed to the properly functionalized endo-amines 3, 5 and 12. Entry to the azawurtzitane system and its corresponding abeo-compounds was achieved by three different cyclization procedures: aminomercuration with mercuric acetate in water (3 → 14, 5 → 16) , olefin amination with mercuric acetate in dimethyl sulfoxide (3 → 18, 5 → 20 + 21) and intramolecular attack at an epoxide (12 → 24 + 25). Molecular rearrangements of 3-azawurtzitanes to 3(4 → 5)abeo-3-azawurtzitanes and vice versa are described involving neighbouring group participation of the N (3) atom.     

Synthesis of propyl O-(α-L-rhamnopyranosyl)-(1→3)-[2,4-di-O-(2s-methylbutyryl)-α-L-rhamnopyranosyl]-(1→2)=(3-O-acetyl-β-D-glucopyranosyl)-(1→2)-βp-D-fucopyranoside,the tetrasaccharide moiety of Tricolorin A

Propyl O-(α-L-rhamnopyranosyl)-(1→3)-[2,4di-O-(2s-methylbutyryl)-α-L-rhamnopyranosyl]-(1→2)-(3-O-acetyl-β-glucopyranosyl)-(1→2)-β-D-fucopyranoside (1), the tetrasaccharide moiety of Ricolorin A, was synthesized in total 23 steps with a longest linear sequence of 10 steps, and overall yield of 3.7% from D-Glucose. The isomerization of the dioxolane-type benzylidene in the prance of NIS/AgOTf was observed. Tetrasaccharide 1 exhibited no activity against the cultured P388 cell as Tricolorin A did.     

Zur Frage der Koordinationsweise von Chromkomplexen aus dem Azofarbstoff 1-Amino-2-hydroxy-naphtalin-4-sulfonsäurepiperidid →→ 1-Phenyl-3-methyl-5-pyrazolon

On chroming the dyestuff 1-amino-2-hydroxy-naphthalene-4-sulfonic acid piperidide → 1-phenyl-3-methyl-5-pyrazolone, only one 1:2 chromium complex is formed. This fact as well as the absorption spectra and the great stability of the complex indicate that the complex must be coordinated in the Drew-Pfitzner arrangement, and that the sandwich arrangement must be excluded. Since the steric structure of the 1:2-complex is already preformed in the adequate 1:1-complex, our results disprove the conclusions presented by IDELSON et al. [1] [3].     

Synthesis of β-（ 1→6）-Branched （ 1→3）-Glucononaoside with Alter-nate β- and α-Bonds in the Backbone

Lauryl glycoside of β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]β-D-Glcp was synthesized through 3 3 3 strategy. 3-O-Allyl-2,4,6-tri-O-benzoyl-β-D-glucopyranosyl-(1→3)- -[2, 3, 4, 6-tetra-O-benzoyl-β-D-glucopyranosyl-(1→6)-] 1,2-O-isopropylidene-α-D-glucofuranose was used as the key intermediate which was converted to the corresponding trisaccharide donor and acceptor readily.