Electrosyntheses of disaccharides from phenyl or ethyl 1-thioglycosides

Constant current electrolyses of the glycosyl donors phenyl and ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-d-glycopyranoside in dry acetonitrile in the presence of various primary and secondary sugar alcohols, performed in an undivided cell, gave β-linked disaccharide derivatives selectively in good yields. Phenyl 2,3,4,6-tetra-O-benzoyl-1-thio-β-d-glycopyranoside gave the β-glucosides exclusively in good to moderate yields.     

Further studies of the ability of xyloglucan oligosaccharides to inhibit auxin-stimulated growth

The structural features required for xyloglucan oligosaccharides to inhibit 2,4-dichlorophenoxyacetic acid-stimulated elongation of pea stem segments have been investigated. A nonasaccharide (XG9) containing one fucosyl-galactosyl side chain and an undecasaccharide (XG11) containing two fucosyl-galactosyl side chains were purified from endo-β-1,4-glucanase-treated xyloglucan, which had been isolated from soluble extracellular polysaccharides of suspension-cultured sycamore (Acerpseudoplatanus) cells and tested in the pea stem bioassay. A novel octasaccharide (XG8′) was prepared by treatment of XG9 with a xyloglucan oligosaccharide-specific α-xylosidase from pea seedlings. XG8′ was characterized and tested for its ability to inhibit auxin-induced growth. All three oligosaccharides, at a concentration of 0.1 microgram per milliliter, inhibited 2,4-dichlorophenoxyacetic acid-stimulated growth of pea stem segments. XG11 inhibited the growth to a greater extent than did XG9. Chemically synthesized nona- and pentasaccharides (XG9, XG5) inhibited 2,4-dichlorophenoxyacetic acid-stimulated elongation of pea stems to the same extent as the same oligosaccharides isolated from xyloglucan. A chemically synthesized structurally related heptasaccharide that lacked a fucosyl-galactosyl side chain did not, unlike the identical heptasaccharide isolated from xyloglucan, significantly inhibit 2,4-dichlorophenoxyacetic acid-stimulated growth.     

Timing of oral morphogenesis and its relation to commitment to division in Paramecium tetraurelia

The interval between commitment to division and fission in synchronous cell samples is a constant fraction of the cell cycle (0.2) in cell cycles up to 6.5 h in duration. In longer cell cycles this interval has a fixed duration of about 80 min. The point of commitment to division is associated with the six-rowed anlage stage of oral primordium development (stage V). At this stage cells carrying the cc1 mutation are not blocked by transfer to restrictive conditions but rather proceed to division. Stage V is also the stabilization point for oral anlagen. When shifted to restrictive conditions prior to this stage, development is arrested and resorption of anlagen is initiated. The cc1 mutation also blocks contractile vacuole duplication and migration under restrictive conditions. The cc1 gene function is required continuously prior to the transition point. The timing of morphogenetic stages in asynchronous cells is roughly similar to that in synchronous cells. There are, however, significant differences in timing as estimated by the two experimental procedures.     

Synthèse des 2-acé-tamido-2-désoxy-6-O-α-et β-D-xylopyranosyl-α-D-glucopyranose

2-Acetamido-2- deoxy-6-O-, -xylopyranosyl-O-D-glucopyranose has been synthesized in crystalline form by condensation of 2,3,4-tri-O-acetyl-α-D-xylopyranosyl chloride (1) with benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-β-D-glucopyranoside (2), followed by O-deacetylation and catalytic hydrogenation. Condensation of 2 with 2,3,4-tri-O-chlorosulfonyl-β-D-xylopyranosyl chloride, followed by dechlorosulfonylation and acetylation, gave benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-(2,3,4-tri-O-acetyl-α-D-xylopyranosyl)β-D-glucopyranoside in crystalline form. O-Deacetylation, followed by catalytic hydrogenation, gave 2-acetamido-2-deoxy-6-O-α-D-xylopyranosyl-α-D-glucopyranose in crystalline form.     

Effect of pH on the association behavior in aqueous solutions of pig gastric mucin

In this study, dynamic light scattering (DLS), turbidity, and rheo-small angle light scattering (rheo-SALS) methods have been utilized to examine the impact of pH (1 < or = pH < or = 7) on aqueous solutions of noncommercial purified pig gastric mucin. The asymmetric flow field-flow fractionation (AFFFF) measurements established that the mucin sample has a high molecular weight and is polydisperse. DLS measurements on dilute solutions of mucin disclosed large interchain aggregates at pH 2, where the polymer has a low charge density or is uncharged. At lower or higher values of pH, mucin is charged and the tendency of forming interpolymer complexes is affected. In the semidilute concentration regime, pronounced junction zones ('lumps' of polymer) are evolved and a heterogeneous connected network is formed at pH 2, whereas the association structures are disintegrated (smaller 'lumps') at lower or higher pH values due to electrostatic repulsive interactions, and a more homogeneous network is evolved. The DLS and viscosity results at pH 1 indicate the development of a fragmented network, composed of contracted chains that are decorated by some positive charges. The effect of shear flow on the structure of semidilute solutions of mucin was investigated with the aid of rheo-SALS methods. The scattered intensity revealed a strong upturn at low values of the wave vector (q) for mucin solutions at pH 2 and pH 4, which suggests the evolution of large association domains. At these pH values, a flow-induced anisotropy in the 2D SALS patterns in the form of elliptical shapes was observed at high shear rates.     

Oligosaccharides corresponding to the regular sequence of heparin: chemical synthesis and interaction with FGF-2.

It has been proposed that oligosaccharides corresponding to the so-called regular region of heparin/heparan sulfate (HS) bind to fibroblast growth factor-2 (FGF-2). In order to explore the molecular basis of FGF/HS interaction, we describe here the chemical synthesis of a tetra and a hexasaccharide, prepared as methyl glycosides, corresponding to the regular sequence of heparin. The strategy relies on the efficient preparation of three building blocks: a seeding block, an elongating block and a capping block. The hexasaccharide inhibited the binding of FGF-2 on its receptor on human aorta vascular smooth muscle cells with an IC50 value (16+/-1.2 microg/mL) close to that of standard heparin (14.8+/-0.5 microg/mL) whereas the tetrasaccharide was much less potent (IC50 = 127+/-10.5 microg/mL). The hexasaccharide and heparin, inhibited in a dose-dependent manner FGF-2 (30 nM) induced proliferation (IC50 = 23.7+/-1.6 and 30.1+/-1.3 microg/mL, respectively). Under the same experimental conditions, the tetrasaccharide only slightly inhibited the mitogenic effect of FGF-2 (IC50 > 100 microg/mL).     

A synthetic heparan sulfate pentasaccharide, exclusively containing L-iduronic acid, displays higher affinity for FGF-2 than its D-glucuronic acid-containing isomers.

It has been suggested that the FGF-2 binding site on heparan sulfate chains is a trisulfated pentasaccharide containing three hexuronic acid units. The configuration at C-5 of two of them being undetermined, we have synthesized the four possible pentasaccharides, and have evaluated their FGF-2 binding affinity through in vitro biological assays. The pentasaccharide containing L-iduronic acid as the sole hexuronic acid showed higher affinity for FGF-2 than the other pentasaccharides, where one hexuronic acid unit at least is D-glucuronic acid.