Saccharide Complexes Research Articles

Evidence That Heparin Saccharides Promote FGF2 Mitogenesis through Two Distinct Mechanisms

Heparin-like saccharides play an essential role in binding to both fibroblast growth factors (FGF) and their receptors at the cell surface. In this study we prepared a series of heparin oligosaccharides according to their size and sulfation level. We then investigated their affinity for FGF2 and their ability to support FGF2 mitogenesis of heparan sulfate-deficient cells expressing FGFR1c. Tetra- and hexasaccharides bound FGF2, but failed to dimerize the growth factor. Nevertheless, these saccharides promoted FGF2-mediated cell growth. Furthermore, whereas enzymatic removal of the non-reducing end 2-O-sulfate group had little effect on the 1:1 interaction with FGF2, it eliminated the mitogenic activity of these saccharides. This evidence supports the symmetric two-end model of ternary complex formation. In contrast, even at very low concentrations, octasaccharide and larger heparin fragments conferred a potent mitogenic activity that was independent of terminal 2-O-sulfation. This correlated with the ability to dimerize FGF2 in an apparently cooperative manner. This data suggests that potent mitogenic signaling results from heparin-mediated trans-dimerization of FGF2, consistent with the asymmetric model of ternary complex formation. We propose that, depending on saccharide structure, there are different architectures and modes of ternary complex assembly that differ in stability and/or efficiency of transmembrane signaling.

Peptide Mimics by Linear Arylamides: A Structural and Functional Diversity Test

Hydrogen-bonded oligoamide foldamers represent a large family of peptide mimics. Pioneered by Gellman and Seebach (Appella , J. Am. Chem. Soc. 1996, 118, 13071- 13072; Seebach , Helv. Chim. Acta 1996, 79, 913- 941), aliphatic amino acid-based mimic structures have been extensively studied. Results of these studies have found many useful applications in areas including chemical biology and drug design. This Account describes our efforts in creating arylamide-based foldamers whose compact conformations are stabilized by hydrogen bonding. The aim of our study was to test whether this class of mimic structures is sufficiently rigid to lead to new interesting functions. It was envisioned that, if our approach was workable, it might be developed into a new family of useful soft frameworks for studies toward molecular recognition, self-assembly, and materials science. Three classes of mimic structures, that is, folded or helical, zigzag, and straight oligomers, have been constructed by simply changing the positions of the substituents at the benzene rings in the backbones. Both amide and hydrazide units have been employed to construct the frameworks. In most cases, O...H-N hydrogen bonding was chosen to stabilize the compact conformations. Notably, for the first time the F...H-N hydrogen-bonding pattern has been used to tune the size of the cavity. To test their usefulness, these frameworks have been extensively modified and functionalized. (1)H NMR, UV-vis, fluorescence, circular dichroism, and X-ray diffraction techniques have all been employed to establish the compact structures and their interactions with guest molecules. The properties or functions of the mimic structures have been studied in seven aspects. (1) Acyclic molecular receptors: The amide foldamers can bind amine cations, while the hydrazide foldamers can complex saccharides. (2) Acceleration of anisole hydrolysis: Several folded oligomers are able to bind alkali metal cations and consequently promote the hydrolysis of the nitro-substituted anisole by alkali hydroxides. (3) Facilitation of macrocyclization: The straight and zigzag backbones can be readily functionalized, from which two classes of macrocycles have been prepared. (4) Homoduplex assembly: Zigzag oligomers that are appended with amide units at one side can form stable homoduplexes through the cooperative self-binding of the amide units. (5) Assembly of molecular tweezers: Discrete binding moieties are introduced at the ends of the oligomers, which can bind structurally matched guests. (6) Assembly of nano networks: F...H-N hydrogen-bonded foldamers can stack with fullerenes; thus a mixture of fullerenes with a trifoldamer generates honeycomb-styled nanoarchitectures. (7) Assembly of dynamic [2]catenanes: A preorganized porphyrin tweezer has been synthesized, from which dynamic three-component [2]catenanes have been assembled in high yields. Our results demonstrate that hydrogen-bonding-driven arylamide oligomers are a class of structurally unique mimic structures. The folded oligomers themselves can be used as synthetic receptors for binding different guest molecules, while incorporation of different segments into one system can produce many desired shapes. In addition, all of the rigid frameworks can be readily functionalized at specific sites. We believe that our results have helped to open the door for some new chemistry in molecular recognition, self-assembly, and other related areas.

Arabinogalactan proteins as molecular markers in Arabidopsis thaliana sexual reproduction

Some of the most important changes that occur in plants during sexual reproduction involve the transition from a sporophytic to a gametophytic type of development. In this paper, these changes were evaluated for Arabidopsis thaliana. The results obtained clearly show differences in the pattern of distribution of specific arabinogalactan protein (AGP) sugar epitopes, during anther and ovule development. AGPs are hydroxyproline-rich glycoproteins that are massively glycosylated and ubiquitous in plants. The molecular mechanism of action of AGPs is still unknown, mainly due to the difficulties posed by the complex saccharide chains. However, the complex structure of the sugar fraction of AGPs makes them a potential source of signalling molecules. The selective labelling obtained with AGP mAbs JIM8, JIM13, MAC207, and LM2, during Arabidopsis pollen and pistil development, suggests that some AGPs can work as markers for gametophytic cell differentiation. Specific labelling of the first gametophytic cells in the pistil, the strong labelling of the secretory cells of the embryo sac, the synergid cells, and the labelling of the integument micropylar cells, apparently outlining the pollen tube pathway into its final target, the embryo sac, have all been shown. In the anthers, the specific labelling of gametophytic cells, and of the male gametes that travel along the pollen tube, may indicate AGP epitopes acting as signals for the pollen tube to reach its final destiny. The specific labelling of cells destined to go into programmed cell death is also discussed.

Vanadyl(IV) complexes with saccharides. Bioactivity in osteoblast-like cells in cultureThis paper is one of a selection of papers published in this Special issue, enititled Second Messengers and Phosphoproteins—12th International Conference.

Complexes of vanadyl(IV) with 4 monosaccharides and 5 disaccharides were tested in 2 osteoblast-like cell lines (MC3T3E1 and UMR106). Many complexes caused stimulation of UMR106 proliferation (120% basal) in the range of 2.5 to 25 micromol/L. In the nontransformed osteoblasts, some vanadyl-saccharide complexes stimulated the mitogenesis (115% basal) in the same range of concentration. The glucose and sucrose complexes were the most efficient inhibitory agents (65% and 88% of inhibition vs. basal, respectively) for tumoral cells at 100 micromol/L. The galactose and turanose complexes exerted a similar effect in the nontransformed osteoblasts. On the other hand, all the complexes promoted the phosphorylation of the extracellular regulated kinases (ERKs). All together, these results indicate that the stimulation of ERKs is not the only factor that plays a role in the proliferative effects of vanadium derivatives since some compounds were inhibitory proliferating agents. Cell differentiation was evaluated by alkaline phosphatase specific activity and collagen synthesis in UMR106 cells. All the complexes inhibited alkaline phosphatase activity, with galactose complex as the most effective compound (IC50 = 43 micromol/L). The complex with the trehalose TreVO was the most effective agent to stimulate collagen synthesis (142% basal) and glucose consumption (132% basal). A cytosolic tyrosine protein kinase and the kinase-3 of glycogen synthase seem to be involved in the stimulation of glucose consumption by vanadium derivatives. In this series, only TreVO gathered the characteristics of a good insulin mimetic and osteogenic drug. In addition, this complex was a good promoting agent of nontransformed osteoblast proliferation, whereas it inhibited tumoral osteoblasts. GluVO, the complex with glucose, was also more toxic for tumoral than for nontransformed cells. These 2 vanadium derivatives are good potential antitumoral drugs. All the results suggest that the biological effects of vanadium compounds are a complex phenomenon influenced by the complexation, the dose, and the nature of the ligands and the cells.

PH Dependent Equilibria of Poly(anilineboronic acid)‐Saccharide Complexation in Thin Films

AbstractSummary: The complexation of saccharides with poly(anilineboronic acid) as a function of pH has been studied with simultaneous measurements of open‐circuit potential and mass change. This study provides an insight into this reaction as well as the relationship between complexation and open‐circuit potential and the optimum pH for complexation of D‐fructose and D‐glucose. The optimum pH values for poly(anilineboronic acid)‐D‐fructose and ‐D‐glucose complexation are near the pKa values of the complex reported in homogeneous solution. At physiological pH (7.4), the apparent binding constant of D‐fructose and D‐glucose with poly(anilineboronic acid) is 19.2 and 0.2 M−1, respectively. In contrast, at pH 9.0, the apparent binding constant of D‐glucose with poly(anilineboronic acid) is 12 M−1, double than that of D‐fructose. The decrease in complexation in the polymer films at pH values above the pKa of the complexes is in contrast to the behavior in homogeneous solutions. This trend is observed for both D‐fructose and D‐glucose using open‐circuit potential, mass change and polarization modulated infrared reflection absorption spectroscopic measurements. Also, the complexation is limited in the polymer film, i.e., ≤23% boron is involved. These results suggest that steric and/or electrostatic interactions may play an important role in complexation within polymer films. magnified image

Interactions between iron(III) and sucrose, dextran, or starch in complexes

This paper is aimed to study the nature of iron(III)–saccharide interactions in complexes and to look for new iron-containing drugs for supplementing organisms. Iron(III)-saccharide complexes were synthesized by reacting FeCl 3 and saccharides (rice starch, sucrose, and dextran) in basic solutions and their characteristics were compared with synthetic iron-oxide. Both crystalline and amorphous iron(III) complexes were obtained and identified by X-ray diffraction (XRD). Amorphous samples were chosen to investigate the interactions between iron(III) and saccharides by continuous-flow dissolution experiments. In acidic solution, the rate of iron release from amorphous iron complexes increased with the following order: iron-rice starch≈iron-oxide≪iron-sucrose≈iron-dextran. The colloidal structure of iron-rice starch was proposed to describe its similar dissolution profile with that of iron-oxide.

Secretion of recombinant human fibrinogen by the murine mammary gland

Transgenic animals secreting individual chains and assembled fibrinogen were produced to evaluate the capacity of the mammary gland for maximizing assembly, glycosylation and secretion of recombinant human fibrinogen (rhfib). Transgenes were constructed from the 4.1 kbp murine Whey Acidic Protein promoter (mWAP) and the three cDNAs coding for the Aalpha, Bbeta and gamma fibrinogen chains. Transgenic mice secreted fully assembled fibrinogen into milk at concentrations between 10 and 200 microg/ml, with total secretion of subunits approaching 700 microg/ml in milk. Partially purified fibrinogen was shown to form a visible and stable clot after treatment with human thrombin and factor XIII. The level of assembled fibrinogen was proportional to the lowest amount of subunit produced where both the Bbeta and gamma chains were rate limiting. Both the Bbeta and gamma chains were glycosylated when co-expressed and the degree of saccharide maturation was dependent on expression level, with processing preferred for gamma chains over Bbeta chains. Also, the subunit complexes gamma2, Aalphagamma2 and the individual subunits Aalpha, Bbeta and gamma were found as secretion products. When the Bbeta was secreted individually, the glycosylation profile of the molecule was of a mature complex saccharide indicating recognition of the molecule by the glycosylation pathway without association with other fibrinogen chains. To date secretion of Bbeta chain has been not observed in any cell type, suggesting that the secretion pathway in mammary epithelia is less restrictive than that occurring in hepatocytes and other cells previously used to study fibrinogen assembly.

Mono- and oligosaccharide sensing by phenylboronic acid-appended 5,15-bis(diarylethynyl)porphyrin complexes

Porphyrin derivatives bearing a pair of boronic acid groups ( 1 , 1·Zn , and 1·Cu ) were designed and synthesized from 2 to construct a saccharide sensing system. Compounds 1 , 1·Zn , and 1·Cu have a diethynyl porphyrin rotational axis, which is expected to act as a saccharide-binding modulator. Saccharide binding studies were conducted by UV–vis, fluorescence, and circular dichroism (CD) spectroscopies. In a water–methanol 1:1 (v/v) mixed solvent, we have found that 1·Zn can bind mono- and oligosaccharides including Lewis oligosaccharides to produce 1:1 host–saccharide complexes with the association constants of 10 2−10 3 M −1 range. This paper thus demonstrates a new principle to design a boronic acid-based saccharide receptor.

A New Reactivity‐Based One‐Pot Synthesis of N‐Acetyllactosamine Oligomers.

Poly-N-acetyllactosamine oligomer is a type-2 glycan core from which a number of important bioactive glycoconjugates are assembled in vivo. Development of an effective synthesis of N-acetyllactosamine oligomers will therefore provide a new chemoenzymatic entry to this class of complex saccharides. This paper describes the design and synthesis of thioglycoside building blocks, determination of their relative reactivity values, and demonstration of their use in the programmable one-pot synthesis of various N-acetyllactosamine oligomers. Through a combination of segment condensation, the strategy allows for the preparation of larger oligosaccharides with minimal protecting group manipulation, as illustrated in the synthesis of an octasaccharide in a very short period of time.

A new reactivity-based one-pot synthesis of N-acetyllactosamine oligomers.

Poly-N-acetyllactosamine oligomer is a type-2 glycan core from which a number of important bioactive glycoconjugates are assembled in vivo. Development of an effective synthesis of N-acetyllactosamine oligomers will therefore provide a new chemoenzymatic entry to this class of complex saccharides. This paper describes the design and synthesis of thioglycoside building blocks, determination of their relative reactivity values, and demonstration of their use in the programmable one-pot synthesis of various N-acetyllactosamine oligomers. Through a combination of segment condensation, the strategy allows for the preparation of larger oligosaccharides with minimal protecting group manipulation, as illustrated in the synthesis of an octasaccharide in a very short period of time.

Nitrocellulose Filter Binding to Assess Binding of Glycosaminoglycans to Proteins

This chapter outlines how the trapping of protein–saccharide complexes onto nitrocellulose filters can be used to explore the protein-binding potential of saccharide motifs. The method provides information on the size of saccharide epitopes recognized by proteins, as well as on affinity constants for these interactions. It may be applied in a preparative mode to yield saccharide fractions for structural analysis. The protocols that are presented describe the standard procedures for fragmentation and radiolabeling of heparin/heparan sulfate (HS). The isolation of HS-derived oligosaccharides to be tested as ligands is also focused. on Proteins are trapped onto nitrocellulose filters along with any bound saccharide ligand. Saccharides that do not bind to the protein are not retained by the filter. The filter-trapping procedure discussed is ideally suited for the screening of different proteins, available in limited quantities, regarding the ability to bind a defined radiolabeled saccharide ligand, a whole chain or an excised oligosaccharide fragment. Characterization of protein-binding saccharide domains that may be estimated by trapping experiments using series of oligosaccharides of different size is presented.

Regioselective Benzoylation of Sugars Mediated by Excessive Bu2SnO: Observation of Temperature‐Promoted Migration.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Regioselective benzoylation of sugars mediated by excessive Bu 2SnO: observation of temperature promoted migration

Regioselective benzoylation of carbohydrates using an excess of dibutyltin oxide (Bu 2SnO) at increased reaction temperatures has been developed for the synthesis of several glycoside benzoates with one or two free hydroxyl groups, including galactosides, glucosides, mannosides and lactosides in high yields. These compounds are useful as building blocks for the synthesis of complex saccharides and derivatives.

Food-Derived Carbohydrates — Structural Complexity and Functional Diversity

ABSTRACT: Carbohydrates are biomolecules abundantly available in nature. They are found in bewildering types ranging from simple sugars through oligo- and polysaccharides to glycoconjugates and saccharide complexes, each exhibiting characteristic bio-physiological and/or nutritional functions both in in vivo and in vitro systems. For example, their presence or inclusion in food dictates the texture (body) and gives desirable customer appeal (satisfaction), or their inclusion in the diet offers beneficial effects of great therapeutic value. Thus, carbohydrates are integrally involved in a multitude of biological functions such as regulation of the immune system, cellular signaling (communication), cell malignancy, antiinfection responses, host-pathogen interactions, etc. If starch is considered the major energy storage carbohydrate, the gums/mucilages and other non-starch carbohydrates are of structural significance. The most investigated properties of starch are its gelatinization and melting behavior, especially during food processing. This has led to the development of the food polymer science approach, which has enabled a new interpretive and experimental frame work for the study of the plasticizing influence of simple molecules such as water, sugars, etc. on food systems that are kinetically constrained. Starch, although considered fully digestible, has been challenged, and starch is found to be partly indigestible in the GI tract of humans. This fraction of starch-resisting digestion in vivo is known as resistant starch (RS). The latter, due to its excellent fermentative capacity in the gut, especially yielding butyric acid is considered a new tool for the creation of fiber-rich foods, which are of nutraceutical importance. By a careful control of the processing conditions the content of RS, a man-made fiber, can be increased to as high as 30%. Arabinoxylans are the major endospermic cell wall polysaccharides of cereals. In wheat they are found complexed with ferulic acid esters, which after oxidative coupling in vivo mediated by H2O2 and peroxidases or even by photochemical means give cross linked diferuloyl derivatives. The latter confer strength and extensibility to the cell wall and offer resistance for digestibility by ruminants. They also help blocking of the ingress of pathogens. The ester bound ferulic acid after oxidation in vivo generates reactive oxygen species that contribute to the fragmentation of non-starch polysaccharides (hemicelluloses), and thereby reduces the product viscosity, a property seen during long-term storage of rice. In plant tissues, the arabinogalactans are implicated in such diverse functions as cell-cell adhesion, nutrition of growing pollen tubes, response to microbial infections, and also as markers of identity expressed in the terminal sequences of saccharide chains.

A hydrogen-bonding receptor that binds cationic monosaccharides with high affinity in methanol.

A dicarboxylate host (1) binds cationic monosaccharides such as D-glucosamine HCl (2), D-galactosamine-HCl (3), and D-mannosamine-HCl (4) with high affinity (K1 = 8.0 x 10(4)-2.0 x 10(5) M(-1)) in methanol. In circular dichroism (CD) spectroscopy a positive exciton-coupling band was observed near 290 nm; this indicates that the saccharides are recognized by multiple point interactions. Since the corresponding neutral monosaccharides are not significantly bound, one may conclude that complex formation is primarily due to the electrostatic interaction between NH3+ in the guest and one carboxylate in the host and secondarily due to hydrogen-bonding interactions of OH groups with the other carboxylate and/or nitrogen bases. Molar ratio plots and Job plots indicate that host 1 and cationic monosaccharide guests form CD-active, pseudo-cyclic 1:1 complexes at low guest concentration followed by the formation of CD-silent, acyclic 1:2 1-saccharide complexes at high guest concentration. The possible binding modes are discussed in detail on the basis of molecular mechanics calculations and chemical shift changes in 1H NMR spectra. The results of competition experiments with several cationic reference compounds bearing fewer OH groups than 2-4 are consistent with the proposed binding model. Thus, the present study is a rare example of saccharide recognition in a protic solvent, where in general, hydrogen-bonding interactions are rarely useful because of strong solvation energy. These are apparently the strongest saccharide complexes involving noncovalent interactions between host and guest. We believe that the findings are significant as a milestone toward development of new saccharide recognition systems ultimately useful in aqueous solution.

Novel water-soluble porphyrin-based receptors for saccharide recognition

A binding study of porphyrin phosphonates ( 1, 2), porphyrin–oligopeptide conjugates ( 3– 5), porphyrin–fluorescein ( 6), and porphyrin–methyl red ( 7) conjugates to saccharides and alkyl pyranosides showed strong interaction in aqueous media and DMSO. The UV–Vis, fluorescence, 1H-, 31P-NMR, and IR spectroscopy were used to study the mechanisms of complexation. Participation of hydrogen bonds in the formation of porphyrin–saccharide complexes was demonstrated.

Neutron Laue diffraction experiments on a large unit cell: concanavalin A complexed with methyl-α-D-glucopyranoside

A neutron Laue diffraction experiment on a complex of concanavalin A with methyl-α-D-glucopyranoside extensively soaked in D2O (space groupI213,a= 167.8 Å), which resulted in 3.5 Å diffraction data, is described. In a programme of structural studies of crystalline saccharide complexes of concanavalin A, the unit cell of the cubicI213 complex of concanavalin A with methyl-α-D-glucopyranoside is one of the largest. With its cell edge of 167.8 Å and its asymmetric unit of molecular weight 50 kDa, it represents a challenge for current neutron diffraction technology. The size of the crystal used in this experiment, although large (4 × 3 × 2 mm), was not the largest ever produced for this complex. The degree of spatial overlapping observed in the Laue experiment, however, suggests that use of larger crystals would be a disadvantage. On the basis of these observations, several technical improvements for macromolecular neutron crystallography are suggested.

Novel porphyrin based receptors for saccharide recognition in water

A binding study of the porphyrin phosphonates ( 1, 2), porphyrin–oligopeptide conjugates ( 3– 5) and meso-tetrakis-( p-sulfonato-phenyl) porphyrin ( 7) to saccharides and alkyl pyranosides showed strong interaction in water and DMSO. The 1 H , 31 P NMR, IR-spectroscopy and SPR technique were used for the study of mechanisms of complexation and potential using of receptors as sensor part; participant of hydrogen bonds in porphyrin–saccharide complexes formation was demonstrated.

Interaction of saccharides with rare earth metal ions: synthesis and characterisation of Pr(III) and Nd(III)saccharide complexes

A number of complexes are synthesised with Pr(III) and Nd(III) employing the mono- and disaccharides, d-glucose, d-galactose, d-mannose, d-arabinose, d-ribose, d-xylose, maltose and lactose. The complexes are characterised by various spectral and analytical techniques, and based on these data, appropriate structures were assigned for all complexes.

Chirality sensing of saccharides using a boronic acid-appended chiral ferrocene derivative

A diboronic acid-appended chiral ferrocene derivative ( R )-9 was designed and synthesized. This chiral ferrocene scaffold was obtained by resolution of the diastereomer with a monosaccharide derivative. One can therefore expect that ( R )-9 would show d/ l selectivity for specific monosaccharides. The complex formation of ( R )-9 with various saccharides using the two boronic acid functions was conveniently monitored by a change in the circular dichroism (CD) spectra. The CD spectral change (Δ[ θ]) induced by added monosaccharides was chiroselective: in particular, d/ l-alloses and d/ l-galactoses induced the 8.0- and 7.0-fold difference in the magnitude of the CD spectral change. The association constants for d- and l-saccharides ( K D and K L, respectively) were determined: among them, ( R )-9 showed a significant discrimination ability for mannose ( K L/ K D=2.6) and arabinose ( K L/ K D=1/2.4). The origin of d/ l selectivity was discussed on the basis of computational studies on ( R )-9·saccharide complexes.