Synthesis of precursors for the dimeric 3-O-SO3Na Lewis X and Lewis A structures

Stereoselective syntheses of 3-O-SO₃Na-β-Gal-(1 → 4)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)-GlcNAc-β-OBn (15) and 3-O-SO₃Na-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 3)-β-GlcNAc-(1 → 3)-β-Gal-(1 → 4)-Glc-β-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl

Full-size image

(8) and ethyl

Full-size image

(18).     

Structure of an acidic microcapsular glycan from the reference strain (C.D.C. 866-57) for Serratia marcescens serogroup 01

The structure of the acidic polysaccharide from Serratia marcescens serogroup O1 has been investigated. NMR spectroscopy together with sugar and methylation analysis have been used as well as a uronic acid degradation. The polysaccharide consists of pentasaccharide repeating units having the following structure.

Full-size image

The polysaccharide also contains one equivalent of O-acetyl groups per repeating unit present on, inter alia, a hydroxymethyl group.     

Structure of a rhamnan from the surface-layer glyco-protein of Bacillus stearothermophilus strain NRS 2004/3a

The structure of a glycan from the surface-layer glycoprotein of Bacillus stearothermophilus strain NRS 2004/3a has been studied by ¹H- and ¹³C-n.m.r. spectroscopy. The results indicate the glycan to be a polymer of the trisaccharide repeating-unit

Full-size image

     

Determination of the structure of a fucose-containing trisaccharide monophosphate isolated from human pregnancy urine

A new acidic oligosaccharide, isolated from the urine of a pregnant women by gel filtration and ion-exchange chromatography, was shown on the basis of sugar analysis, methylation analysis, exo-glycosidase digestion, e.i.-m.s., f.a.b.-m.s., and n.m.r. spectroscope to have the following structure:

Full-size image

     

Glycosylation with N-Troc-protected glycosyl donors

N-Troc-protected (Troc = 2,2,2-trichloroethoxycarbonyl) glucosamine and galactosamine glycosyl donors (1-O-acetyl sugar, bromo sugar, and thioglycoside) were compared with the corresponding N-Phth-protected derivatives in glycosylations of 2-(trimethylsilyl)ethanol, 2-bromoethanol, methyl 3-mercaptopropionate, N-Fmoc-protected serine, and 2-(trimethylsilyl)ethyl

Full-size image

. The N-Troc-protected donors gave pure β-glycosides in somewhat higher yields than the N-Phth-protected counterparts. The N-Troc protecting group can be removed by reduction with zinc, which allows selective N-deprotection in oligosaccharides containing both N-Troc and N-Phth groups.     

Structural studies of the O-antigen from Vibrio cholerae O:21

The O-antigen from Vibrio cholerae O:21 has been investigated, using n.m.r. spectroscopy, methylation analysis, and Smith degradation as the main methods. It is concluded that the O-antigen is composed of tetrasaccharide repeating-units having the following structure (in which Hep = -glycero- -manno-heptose).

Full-size image

     

Structure determination of a novel uronic acid residue isolated from the exopolysaccharide produced by a bacterium originating from deep sea hydrothermal vents

The exopolysaccharide produced by the bacterium Alteromonas sp. strain 1644 originating from deep sea hydrothermal vents was shown to contain a novel glucuronic acid derivatives:

Full-size image

acid. The structure of this compound was established on the basis of mass spectrometric data, methylation analysis, preparation of derivatives, and chemical synthesis of references compounds.     

A stereocontrolled synthetic approach to glycopeptides corresponding to the carbohydrate-protein linkage region of cell-surface proteoglycans

The glycopeptides 1

Full-size image

and 2

Full-size image

), carrying the core structure of serine-linked cell-surface proteoglycans were synthesized in a stereocontrolled manner. The carbohydrate key imidate xylosyl donors 3 and glycotetraosyl donors 4 and 5, as well as a tetrapeptide glycosyl acceptor 6, were coupled in the crucial glycosylation step. In these reactions, the application of either trimethylsilyl trifluoromethanesulfonate (TMSOTf) or borontrifluoride etherate (BF₃-Et₂O) as catalysts proved to be highly efficient. The serine linked glycopeptides 34, 36 and 37 thus obtained yielded target compounds 1 and 2 on complete deprotection.     

An efficient synthesis of methyl tetra-o-hexyl gentiooctaoside, an octaosyl analogue of ANP receptor antagonist HS-142-1

Methyl

Full-size image

, a 3-O hexyl analogue of the octaosyl component of fungal lipooligosaccharide HS-142-1, was stereo- and regioselectively synthesized as a potent antagonist for the tetrameric atrial natriuretic peptide (ANP) receptors.     

The structure of the O-antigenic chain of the lipopolysaccharide of Rhizobium trifolii 4s

The structure of the O-antigen chain of the lipopolysaccharide (LPS) of Rhizobium trifolii 4s has been determined by a combination of chemical and spectroscopic methods. The glycosyl components were found to be -rhamnose, N-acetyl- -glucosamine, and N-acetyl- -mannosamine in 3:1:1 molar proportion, as determined by gas chromatography and gas chromatography-mass spectrometry of alditol acetate and persilylated (R)-2-hydroxybutyl glycoside derivatives. The linkage positions and configurations of the glycosyl residues were obtained by 1D and 2D NMR spectroscopy. The polymer has a pentasaccharide repeating-unit containing rhammose and N-acetylglucosamine in the main chain and N-acetylmannosamine as the sole-side chain component. This latter residue is linked to a main-chain rhamnose residue. This result was suggested by NMR spectroscopy and confirmed by periodate oxidation. The sequence was deduced by 1D and 2D NMR NOE experiments and by partial hydrolysis studies. The repeating unit of the polysaccharide is shown. This constitutes the first complete structure of an O-antigenic chain of the lipopolysaccharide of any strain of Rhizobium trifolii.

Full-size image

     

The exopolysaccharides produced by Streptococcus thermophilus Rs and Sts have the same repeating unit but differ in viscosity of their milk cultures

The polysaccharides produced by Streptococcus thermophilus Rs and Sts in skimmed milk consist of -Gal and -Rha in a molar ratio of 5:2. Linkage analysis and 1D/2D NMR (¹H and ¹³C) studies revealed that both polysaccharides have the same branched heptasaccharide repeating unit:

Full-size image

Remarkably, the two strains differ in their effects on the viscosity of stirred milk cultures. The milk culture of S. thermophilus Rs is non-ropy and affords 135 mg/L polysaccharide with an average molecular mass of 2.6×10³ kDa. In contrast, the milk culture of S. thermophilus Sts is ropy and produces 127 mg/L polysaccharide with an average molecular mass of 3.7×10³ kDa. Permeability measurements of non-stirred milk cultures of both strains suggest that both strains have a similar effect on the protein–polysaccharide network. Therefore, the only clear difference between both strains, which may cause the difference in ropiness of the milk cultures, is the difference in molecular mass of the polysaccharide.     

Formation of a metallocycle by dimerization of acrylonitrile. Crystal structure of the hexakis{(1,4-dicyanobutane-1,4-diyl)-nickel(II)} complex

A novel hexanickel(II) complex [Ni₆(NCCHCH₂CH₂CHCN)₆] (2) with 1,4-dicyanobutane-1,4-diyl (L) which was produced by the metal-induced dimerization of acrylonitrile (AN) has been isolated and the structure has been determined crystallographically. Complex 2 is triclinic, space group

Full-size image

. Each nickel atom is coordinated by two carbon atoms of L and two nitrogen atoms of the cyano group of two other L, providing a square-plenar geometry. The six nickel atoms are bridged by the cyano group and carbon atom to form the slightly distorted octahedral Ni₆ core.     

Synthesis of enantiomerically pure lysophosphatidylinositols and alkylphosphoinositols

A convenient synthesis for enantiomeric pure

Full-size image

,

Full-size image

(or and (or has been described. Starting from myo-inositol, penta-O-acetyl-myo-inositol was made in five steps. Then enantiomeric purification was done by a diastereomeric salts separation method, and the purity of each enantiomer was spectroscopically measured (¹⁹F-NMR). The phosphodiester was made via phosphoramidites. The enantiomeric products (>99% optical purity) of all compounds were easily obtained in large quantities (5–10 g). Synthetic phosphatidylinositol analogues of precisely defined structure and configuration are interesting tools for studying signal transduction mechanism and cell activity modulation.     

Effet de la longueur d'onde de préillumination sur la désactivation des formes oxydées du donneur d'électrons du Photosystème II

Effect of preillumination wavelength on the deactivation of oxidized forms of the Photosystem II electron donor

Deactivation was studied using chlorella cells or spinach chloroplasts after an illumination of different wavelengths (light I = 710 nm, light II = 650 or 480 nm). The measurements concerned mainly the third oxidized state S₃ of the System II electron donor, according to the scheme proposed by

Full-size image

, (Photochem. Photobiol., 11 (1970)457). The time course of deactivation was followed during the dark after each preillumination. Different results were obtained with algae in state 1 or state 2 as defined by

Full-size image

, (Biochim. Biophys. Acta, 189 (1969) 366). In state 1 the deactivation of S₃ is faster after light 11 than after light 1; in state 2, except at the beginning of the decay, the deactivation of S₃ is almost the same after the two kinds of preillumination. With chloroplasts the deactivation is slower, but always faster after light II than after light I, no transition between state 1 and state 2 was observed. The results are discussed with reference to the possible reducing substrates of the reaction.     

Lipid composition of adult Foleyella agamae

Full-size image

& Obiamiwe B. A. 1986. Lipid composition of adult Foleyella agamae. International Journal for Parasitology 16: 655–657. The lipid and fatty acid composition of the filarial parasite Foleyella agamae were investigated. Total lipids accounted for 7.05% of the parasite fresh weight. Neutral lipids comprised 56.34% of the total and polar lipids 43.66%. The major lipid classes detected include sterol esters, cholesterol, phosphatidyl choline and phosphatidyl ethanolamine. Fatty acids varying in chain length from 10 carbon atoms through 20 carbon atoms were identified in the total lipid extract. The 18 carbon fatty acids formed the predominant components. The 20 carbon fatty acids were confined to the polar lipds.     

Extracellular polysaccharide of Erwinia chrysanthemi Ech6

Many strains of Erwinia chrysanthemi, which are Gram-negative bacterial phytopathogens, produce copious amounts of extracellular polysaccharides. The extracellular polysaccharide from E. chrysanthemi pv. zeae strain SR 260, a phytopathogen of corn, is a branched-chain glucomannorhamnan of proven structure (Gray et al., Carbohydr. Res. 1993, 245, 271–287). The extracellular polysaccharide from E. chrysanthemi Ech6 is different, containing no rhamnose or mannose. It is composed of -fucose, -galactose, -glucose and -glucuronic acid in the ratio 2:2:1:1. The structure of the polysaccharide is as follows:

Full-size image

     

The impact of aromatase mechanism on other P450s

Experimental findings from a number of laboratories have converged to show that the conversion of androgens into oestrogen, catalysed by aromatase, involves three distinct reactions which occur at a single active site. That each one of these reactions belongs to a different generic type was revealed by chemical consideration, together with our ¹⁸O-experiments. In particular, these findings high-lighted the fact that the third reaction in the sequence occurs by a novel process for which a number of plausible mechanisms have been considered. The scrutiny of these mechanisms has involved either studies on aromatase itself, or on related enzymes which catalyse the aromatase type of cleavage reaction as generalized in equation 1:

Full-size image

The acyl-carbon cleavage reaction of equation 1 is catalysed by sterol 14-demethylases, accounts for several side-chain fission products formed by CYP17 (17-hydroxylase-17,20-lyase), and constitutes a weak property of certain drug metabolizing P450s, when given aliphatic aldehydes as substrates. From cumulative studies on these enzymes, consensus is beginning to emerge that the acyl-carbon fission may be promoted by the Fe^III---OOH intermediate, formed during the catalytic cycles of P450s. The precedent for the direct involvement of the Fe^III---OOH species in the reaction of equation 1 is influencing our thinking regarding the mechanism of the conventional hydroxylation reaction. The status of knowledge surrounding the current debate on these issues will be reviewed.     

Light-induced absorbance changes in Fraction I particles prepared from spinach chloroplasts by French-press treatment

Light-induced changes of absorbance were measured in Fraction 1 particles prepared from spinach chloroplasts according to a method developed by

Full-size image

⁶ that employs breakage of chloroplasts in the French pressure cell and centrifugation of the resulting fragments on a sucrose density gradient. Absorbance changes were measured in the presence of ascorbate and 2,3,5,6-tetramethyl-1,4-phenylenediamine as an electron donating system. In addition to the oxidation of P₇₀₀ and cytochrome f, that was investigated in our previous study¹¹, three other light-induced absorbance changes were observed; reduction of cytochrome b with a peak at 562 nm, the so-called 515-nm change showing an absorbance increase at 515 nm and a decrease at 480 nm, and a broad band of unknown absorbance increase covering wave-lengths from 490 to 570 nm. Uncouplers such as carbonylcyanide-m-chlorophenylhydrazone and gramicidin D inhibited the 515-nm change under continuous light and accelerated the dark decay of flash-light-induced change. The other broad absorbance change was insensitive to these inhibitors.     

Cross-flow Microfiltration of Saccharomyces cerevisiae

A model which predicts the filtrate flux and the pressure drop over the length of a cross-flow hollow-fibre microfilter is presented. Data from a series of 128 experimental runs were fitted using a multi-variable, non-linear regression program. Average errors of less than 10% were found. The final equations of average flux and pressure drop were:

Full-size image

     

The PHBH fold: Not only flavoenzymes

p-Hydroxybenzoate hydroxylase,

Full-size image

-amino acid oxidase, cholesterol oxidase and glucose oxidase form a family of structurally related flavoenzymes. Comparison of their three-dimensional structures reveal how the same FAD-binding scaffold has been employed to implement diverse active-site architectures, suited for different types of catalytic reactions. The substrate binding mode differs in each of these enzymes, with the catalytically relevant residues not located on homologous positions. A common feature is provided by the ability of these enzyme to bury their substrates beneath the protein surface. In

Full-size image

-amino acid oxidase and cholesterol oxidase, a loop forms a ‘lid’ controlling the active site accessibility, whereas in p-hydroxybenzoate hydroxylase is the flavin itself, which swings out to allow substrate binding. The crystallographic analysis has revealed that the GTP-dissociation inhibitor of RAB GTPases has a folding topology remarkably similar to p-hydroxybenzoate hydroxylase. This finding highlights the versatile nature of this folding topology, which in addition to flavin-dependent catalysis, is suited for diverse functions, such as the regulation of GTPases.