Crystal and molecular structures of substituted α-d-glucopyranosides

The crystal and molecular structures of methyl 2,4,6-tri-O-pivaloyl-α-d-glucopyranoside (1), methyl 4,6-O-(R)-benzylidene-2-O-pivaloyl-α-d-glucopyranoside (2), and methyl 4,6-O-(R)-benzylidene-2,3-di-O-pivaloyl-α-d-glucopyranoside (3) were determined by X-ray analysis. Crystals of 1 are orthorhombic, space group P2₁2₁2₁ with the unit cell a = 13.026(2), b = 16.832, c = 11.929(2) Å, Z = 4. Crystals of 2 are monoclinic, space group P2₁. The unit-cell parameters are a = 6.519(1), b = 14.664(4), c = 10.635(4) Å, β = 93.18(1)°, Z = 2. Crystals of 3 are orthorhombic, space group P2₁2₁2₁ with a = 10.006(3), b = 13.874(3), c = 18.527(5) Å, Z = 4. The structures were solved by MULTAN and refined by a full-matrix procedure to final values of R = 0.084 (1), 0.048 (2), and 0.069 (3). The pyranose ring in each compound adopts the ⁴C₁ conformation. The 1,3-dioxane rings in 2 and 3 show a chair conformation. The molecular packing in 1 is through the hydrogen bonds involving HO-3 and the 6-O-pivaloyl carbonyl group [HO-3 ⋯ O-9, 2.855(8) Å], which connect the molecules into a chain along

. The endocyclic oxygen atom is involved in an intermolecular hydrogen-bond with HO-3 [2.848(4) Å], joining molecules of 2 into the chains along

. There are no free hydroxyl groups in 3 and molecular packing reflects van der Waals interactions only.     

The crystal and molecular structure of α-laminaribiose octa-acetate

The crystal and molecular structure of octa-O-acetyl-α-laminaribiose is compared with those of disaccharides, and their acetylated derivatives, related to polysaccharides of the laminarin and curdlan type. Marked differences are found in the endo- and exo-cyclic torsion angles as well as in the molecular geometry of the glycosidic linkage. The conformation of AcO-6′ provides the first experimental evidence of the theoretically predicted gauche-trans-gauche⁻ conformation. This conformational change, together with the α-orientation of AcO-1, alters the overall shape of the molecule and influences the packing features. The effect of the acetylation is also examined in terms of calculated conformational energy maps.     

Green synthesis,inhibition studies of yeast α-glucosidase and molecular docking of pyrazolylpyridazine amines

An efficient and environmentally benign simple fusion reaction of 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (1a) or 3-chloro-6-(3,5-dimethyl-4-nitro-1H-pyrazol-1-yl)pyridazine (2a) with different aliphatic/aromatic amines have produced a series of novel pyrazolylpyridazine amines (4a–4c & 5a–5m). All compounds exhibited moderate in vitro yeast α-glucosidase inhibition except m-chloro derivative 5g, which was found potent inhibitor of this enzyme with IC₅₀ value of 19.27 ± 0.005 µM. The molecular docking further helped in understanding the structure activity relationship of these compounds including 5g.     

A diastereoselective synthesis of 7α-nitromethyl steroid derivative and its use for an efficient synthesis of eplerenone

A novel and efficient method of stereoselectively introducing α-nitromethyl group to C-7 position of 11α-hydroxyl canrenone 4 was described. In addition, this method was successfully applied in a total synthesis of Eplerenone 8. The route was characteristic of simple operation, moderate reaction conditions with 5 steps and 55% total yield, at the same time, without any expensive or toxic reagent in use.     

Energetics and structure of alanine-rich α-helices via adaptive steered molecular dynamics

The energetics and hydrogen bonding profiles of the helix-to-coil transition were found to be an additive property and to increase linearly with chain length, respectively, in alanine-rich α-helical peptides. A model system of polyalanine repeats was used to establish this hypothesis for the energetic trends and hydrogen bonding profiles. Numerical measurements of a synthesized polypeptide Ac-Y(AEAAKA)_kF-NH₂ and a natural α-helical peptide a2N (1–17) provide evidence of the hypothesis’s generality. Adaptive steered molecular dynamics was employed to investigate the mechanical unfolding of all of these alanine-rich polypeptides. We found that the helix-to-coil transition is primarily dependent on the breaking of the intramolecular backbone hydrogen bonds and independent of specific side-chain interactions and chain length. The mechanical unfolding of the α-helical peptides results in a turnover mechanism in which a 3₁₀-helical structure forms during the unfolding, remaining at a near constant population and thereby maintaining additivity in the free energy. The intermediate partially unfolded structures exhibited polyproline II helical structure as previously seen by others. In summary, we found that the average force required to pull alanine-rich α-helical peptides in between the endpoints—namely the native structure and free coil—is nearly independent of the length or the specific primary structure.     

Mass-spectral fragmentation of methyl 2,3,4-tri-O-methyl-α-D-glucopyranosiduronamide and its analytical application

Fragmentation pathways for methyl 2,3,4-tri-O-methyl-α-D-glucopyranosiduronamide are proposed, based on 70- and 12-eV spectra of the compound specifically labelled with CD₃ and ND₂ groups. The presence of the NH₂ group in the molecule gives rise to new fragmentation series. The number and positions of CD₃ groups can be unequivocally determined from the mass spectra. Partially methylated derivatives of hexuronic acids, obtained by methylation analysis of hexuronic acid-containing substances, can be identified by exhaustive trideuteriomethylation and conversion into readily obtainable crystalline amides.     

Crystal structure and thermostability of a putative α-glucosidase from Thermotoga neapolitana

Glycoside hydrolase family 4 (GH4) represents an unusual group of glucosidases with a requirement for NAD(+), Mn(2+), and reducing conditions. We found a putative α-glucosidase belonging to GH4 in hyperthermophilic Gram-negative bacterium Thermotoga neapolitana. In this study, we recombinantly expressed the putative α-glycosidase from T. neapolitana, and determined the crystal structure of the protein at a resolution of 2.0? in the presence of Mn(2+) but in the absence of NAD(+). The structure showed the dimeric assembly and the Mn(2+) coordination that other GH4 enzymes share. In comparison, we observed structural changes in T. neapolitana α-glucosidase by the binding of NAD(+), which also increased the thermostability. Numerous arginine-mediated salt-bridges were observed in the structure, and we confirmed that the salt bridges correlated with the thermostability of the proteins. Disruption of the salt bridge that linked N-terminal and C-terminal parts at the surface dramatically decreased the thermostability. A mutation that changed the internal salt bridge to a hydrogen bond also decreased the thermostability of the protein. This study will help us to understand the function of the putative glucosidase and the structural features that affect the thermostability of the protein.     

An α-glucan isolated from root of Isatis Indigotica,its structure and adjuvant activity

The root of Isatis indigotica is a traditional Chinese herbal medicine. An α-glucan (IIP-A-1) was firstly isolated from the roots. In this study we elucidated the chemical structure of IIP-A-1 and determined its adjuvant activity by co-immunizing mice with H1N1 influenza virus split and recombinant hepatitis B surface antigen (HBsAg), respectively. The polysaccharide was pretreated with periodate oxidation, Smith degradation and methylation in order to analyze its structure using GC, HPGPC, FT-IR, NMR and GC-MS. The adjuvant effect was evaluated by determining the antibody titers of serum against H1N1 influenza and HBsAg using ELISA. The proliferation and TNF-α secretion of macrophages administrated with different dose of IIP-A-1 were measured in vitro. The results of this study revealed that IIP-A-1 was an α-glucan with the molecular weight of 3,600 Da. The backbone was α-(1?→?4)-D-glucan with (1?→?6) branch chain. The α-glucan could significantly enhance the immune response of mice immunized with H1N1 influenza or HBsAg in vivo and exert good dose-dependent effects on the proliferation and the TNF-α secretion of macrophages in vitro. These results supported that IIP-A-1 was expected to be an efficacious adjuvant candidate for prophylactic and therapeutic vaccines.     

Structure based molecular design, synthesis and biological evaluation of α-pyrone analogs as anti-HSV agent

Several options for treating Herpes Simplex Virus type 1 and type 2 are available. However, non-specific inhibition and drug resistance warrants the discovery of new anti-herpetic compounds with better therapeutic profile or different mode of action. The non-nucleoside inhibitors of HSV DNA polymerase target the site that is less important for the binding of a natural nucleoside or nucleoside inhibitors. In the present study, we have explored the possibility to find a new lead molecule based on α-pyrone analogs as non-nucleoside inhibitors using structure based modeling approach. The designed molecules were synthesized and evaluated for anti-HSV activity using MTT assay. The compound 5h with EC(50) 7.4μg/ml and CC(50) 52.5μg/ml was moderately active against HSV when compared to acyclovir. A plaque reduction assay was also carried out and results reveal that 5h is more effective against HSV-1 with better selective index of 12.8 than against HSV-2 (SI=3.6). The synthesized compounds were also evaluated for anti-HIV activity, but none were active.     

The synthesis and structure of an n-terminal dodecanoic acid conjugate of α-conotoxin MII

Summary The α-conotoxin MII is a 16 amino acid long peptide toxin isolated from the marine snail,Conus magus. This toxin has been found to be a highly selective and potent inhibitor of neuronal nicotinic acetylcholine receptors of the subtype α3β2. To improve the bioavailability of this peptide, we have coupled to the N-terminus of conotoxin MII, 2-amino-D,L-dodecanoic acid (Laa) creating a lipidic linear peptide which was then successfully oxidised to produce the correctly folded conotoxin MII construct.     

Bromine oxidation of methyl α- and β-pyranosides of D-galactose,D-glucose,and D-mannose

Methyl α- and β-pyranosides of D-galactose, D-glucose, and D-mannose have been oxidized with bromine in aqueous solution at various pH values. The resulting keto glycosides were converted into their more-stable O-methyloxime derivatives which were characterized by spectroscopy and chromatography. Oxidation at a ring carbon atom where the hydrogen is axial is hindered by bulky substituents in syn (i.e., a 1,3) diaxial relationship. Thus, the aglycon group in the α anomers protects position 3, the axial HO-4 in galactopyranosides protects position 2, and the axial HO-2 in mannopyranosides protects position 4 from oxidation.     

Molecular and crystal structure of the regenerated form of (1→3)-α-d-glucan

The crystal structure of a regenerated form of (1→3)-α-d-glucan, obtained by solid state deacetylation of the triacetate derivative, has been determined by combined X-ray diffraction analysis and stereochemical model refinement. The structure crystallizes in an orthorhombic unit cell with parameters $\text{a = 16.46}\text{A}\text{?}\text{, b = 9.55}\text{A}\text{?}$ and c (fibre repeat)=8.44 Å, and space group P2₁2₁2₁. The chain conformation is nearly completely extended and is very close to a 2/1 helix, even though the dimer residue is the crystallographic repeat unit. An intramolecular O(2)  O(4)′ hydrogen bond stabilizes the conformation and extensive intermolecular hydrogen-bonding abilizes the packing. The resulting structure is sheet-like, with an alternating polarity of chain directions within the sheet. In its sheet-like character, extensive hydrogen-bonding, and insolubility in water, this polymorph of (1→3)-α-d-glucan resembles regenerated cellulose. The reliability of the structure analysis is indicated by the X-ray residual R=0.206.     

Quantum-chemical investigation of the structure and the antioxidant properties of α-lipoic acid and its metabolites

Quantum-chemical computations were used to investigate the structure-antioxidant parameter relationships of α-lipoic acid and its natural metabolites bisnorlipoic acid and tetranorlipoic acid in their oxidized and reduced forms. The enantiomers of lipoic and dihydrolipoic acid were optimized using the B3LYP/6-311+G(3df,2p), B3LYP/aug-cc-pVDZ and MP2(full)/6-31+G(d,p) levels of theory as isolated molecules and in the presence of water. The geometries of the metabolites and the values of their antioxidant parameters (proton affinity, bond dissociation enthalpy, adiabatic ionization potential, spin density, and the highest occupied molecular orbital energy) were calculated at the B3LYP/6-311+G(3df,2p) level of theory. The results obtained reveal similarities between these structures: a pentatomic, nonaromatic ring is present in the oxidized forms, while an unbranched aliphatic chain (as found in saturated fatty acids) is present in both the oxidized and the reduced forms. Analysis of the spin density and the highest occupied molecular orbital energy revealed that the SH groups exhibited the greatest electron-donating activities. The values obtained for the proton affinity, bond dissociation enthalpy and adiabatic ionization potential indicate that the preferred antioxidant mechanisms for α-lipoic acid and its metabolites are sequential proton loss electron transfer in polar media and hydrogen atom transfer in vacuum.     

Induction of α1-antitrypsin mRNA and cloning of its cDNA

Local inflammation was inflicted in a baboon by turpentine administration in order to induce the plasma level of α1-antitrypsin, an acute phase protein synthesized in the liver. Comparison of the α1-antitrypsin mRNA activity in the induced and non-induced baboon liver indicated that the “acute phase” response to chemical-inflicted inflammation is mediated through an increase in the steady-state level of cellular mRNA. Alpha-1-antitrypsin was then enriched from the induced baboon liver to a purity of greater than 90% by specific immunoprecipitation of polysomes. Double-stranded DNA was synthesized from the enriched mRNA and inserted into the $\text{Pst}$ I site of pBR322. Recombinant clones containing α1-antitrypsin cDNA sequences were identified by hybridselected translation and confirmed by DNA sequence analysis.     

Mono-thioesters and di-thioesters by lipase-catalyzed reactions of α,ω-alkanedithiols with palmitic acid or its methyl ester

1-S-Mono-palmitoyl-hexanedithiol and 1-S-mono-palmitoyl-octanedithiol were prepared in high yield (80–90%) by solvent-free lipase-catalyzed thioesterification of palmitic acid with the corresponding ,-alkanedithiols in vacuo. Similarly, 1,6-di-S-palmitoyl-hexanedithiol and 1,8-di-S-palmitoyl-octanedithiol were prepared in moderate yield (50–60%) by solvent-free lipase-catalyzed thioesterification of palmitic acid with 1-S-Mono-palmitoyl-hexanedithiol and 1-S-mono-palmitoyl-octanedithiol, respectively. An immobilized lipase preparation from Rhizomucor miehei (Lipozyme RM IM) was more effective than a lipase B preparation from Candida antarctica (Novozym 435) or a lipase preparation from Thermomyces lanuginosus (Lipozyme TL IM). Lipase-catalyzed transthioesterifications of methyl palmitate with ,-alkanedithiols using the same enzymes were less effective than thioesterification for the preparation of the corresponding 1-S-mono-palmitoyl thioesters.Dedicated to Professor Dr Helmut K. Mangold, former Executive Director, Federal Centre for Lipid Research, Institute for Biochemistry and Technology, Münster, Germany, on the occasion of his 80th birthday on 19 June 2004     

Synthesis,in vitro evaluation and molecular docking studies of novel amide linked triazolyl glycoconjugates as new inhibitors of α-glucosidase

A series of N-substituted amide linked triazolyl β-d-glucopyranoside derivatives (4a-l) were synthesized and their in vitro inhibitory activity against yeast α-glucosidase enzyme [EC.3.2.1.20] was assessed. Compounds 4e (IC₅₀ = 156.06 μM), 4f (IC₅₀ = 147.94 μM), 4k (IC₅₀ = 127.71 μM) and 4l (IC₅₀ = 121.33 μM) were identified as the most potent inhibitors for α-glucosidase as compared to acarbose (IC₅₀ = 130.98 μM) under the same in vitro experimental conditions. Kinetic study showed that both 4e and 4f inhibit the enzyme in a competitive manner with p-nitrophenyl α-d-glucopyranoside as substrate. Molecular docking studies of 4e, 4f, 4k and 4l were also carried out using homology model of α-glucosidase to find out the binding modes responsible for the inhibitory activity. This study revealed that the binding affinity of compounds 4e, 4f, 4k and 4l for α-glucosidase were −8.2, −8.6, −8.3 and −8.5 kcal/mol respectively, compared to that of acarbose (−8.9 kcal/mol). The results suggest that the N-substituted amide linked triazole glycoconjugates can reasonably mimic the substrates for the yeast α-glucosidase.     

New syntheses of α-methyl- and α,α′-dimethylspermine

-Methylspermine and ,-dimethylspermine were synthesized in high overall yields starting from N-(benzyloxycarbonyl)-3-aminobutanol in order to study polyamine biochemistry in vitro and in vivo.__________Translated from Bioorganicheskaya Khimiya, Vol. 31, No. 2, 2005, pp. 200–205.Original Russian Text Copyright © 2005 by Grigorenko, Vepsalainen, Jarvinen, Keinanen, Alhonen, Janne, Khomutov.