Galactose Derivatives Research Articles

A dimethoxytriazine type glycosyl donor enables a facile chemo-enzymatic route toward α-linked N-acetylglucosaminyl-galactose disaccharide unit from gastric mucin

An efficient chemo-enzymatic process for construction of the α-linked disaccharide unit (GlcNAcα1-4Gal) found in gastric mucin has been developed. The process consists of a one-step preparation of a novel triazine type glycosyl donor in water and the subsequent transglycosylation to a galactose derivative catalysed by α-N-acetylglucosaminidase.

The Crystal Structure of 4,6-Di-O-Benzyl-2,3-Dideoxy-2,2,3,3-Tetrafluorogalactose

The crystal structure of a reducing dibenzylated tetrafluorinated galactose derivative is reported. The compound crystallized as the α-anomer, and a single OH···O hydrogen bond dominates the crystal packing, leading to a helical arrangement containing two galactose derivatives per turn. Interestingly, the helices are cross-linked by ArC–H···F contacts, but without significant Ar–Ar interactions.

Inhibition of Galectins with Small Molecules

Evidence that the galectin family of proteins plays crucial roles in cancer, inflammation, and immunity has accumulated over the last decade. The galectins have consequently emerged as interesting drug targets. A majority of galectin functions occurs by means of cross-linking glycoproteins and by doing so controlling glycoprotein cellular localization and residence times. The glycoprotein cross-linking occurs when galectin dimers or multimers, or galectins with two binding sites, bind galactose-containing glycans of the glycoproteins. Such galectin-glycan interactions have been successfully blocked with compounds having multivalent presentation of galactose, lactose, or N-acetyllactosamine, with peptides, and with small carbohydrate (galactose) derivatives. This review summarizes and analyzes attempts to develop efficient and selective small-molecule galectin inhibitors through derivatization of monosaccharides, mainly galactosides, with non-carbohydrate structures that protrude into subsites adjacent to the core-conserved galactose-recognizing site of the galectins.

Fast classification and compositional analysis of polysaccharides from TCMs by ultra-performance liquid chromatography coupled with multivariate analysis

A reversed-phase ultra-performance liquid chromatographic (UPLC) method is described for the simultaneous determination of aldoses and uronic acids. The separation was carried out on a UPLC™ HSS T3 column (100mm×2.1mm, 1.7μm) using precolumn derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) and UV detection at 250nm, and 9 PMP derivatives of mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose and arabinose were baseline separated within 5.5min. Furthermore, the described method was successfully applied to the quantitative analysis of component monosaccharides in polysaccharides extracted from traditional Chinese medicines (TCMs). The results demonstrated the proposed UPLC method was precise and practical for the analysis of TCM polysaccharides. Finally, principal component analysis (PCA) and linear discriminant analysis (LDA) were used to classify and differentiate 30 polysaccharide samples from five TCMs to provide the basis for guiding reasonable use of TCM polysaccharides and controlling their quality better.

Surface plasmon resonance imaging of glycoarrays identifies novel and unnatural carbohydrate-based ligands for potential ricin sensor development

Carbohydrate microarrays provide access to high through-put analysis of protein–carbohydrate interactions. Herein we demonstrate the use of SPR imaging (SPRi) of glycoarrays to assess the ligand specificity of the reputedly galactose-specific plant lectin RCA120 (Ricinus communis agglutinin 120), a surrogate for the bioterrorism agent ricin. Glycoarray studies identified RCA120 ligands based on galactose substituted at the 6-position with sialic acid. These observations, which were confirmed by saturation transfer difference (STD) NMR spectroscopy studies, inspired the synthesis of non-natural 6-substituted galactose derivatives, which were shown to have ∼3–4 fold enhanced binding to RCA120 with respect to the unsubstituted compound. These novel unnatural galactosides, which are chemically and biologically more robust than their natural glycan counterparts, represent new potential ligands for the development of carbohydrate-based ricin sensors.

Galactose Encapsulated Multifunctional Nanoparticle for HepG2 Cell Internalization

AbstractThe fluorescent dye Cy3 and galactose derivatives are covalently assembled with different ratios on the surfaces of magnetic nanoparticles (MNPs) to produce multifunctional HepG2 cancer cell–targeting agents and the effect of ligand spatial orientation on the MNP surface is investigated on targeting specificity. By using a mixture of bis‐N‐hydroxysuccinimide ester (a bifunctional linker) and OSu‐activated Cy3 (w/w = 30:1), stable and quantifiable fluorescent MNPs (Cy3@MNPs) are synthesized that could be subsequently loaded with galactosyl ligands. A mono‐antennary and two different tri‐antennary galactosyl ligands are individually immobilized on Cy3@MNPs, and the uptake efficiencies of the resulting galactosyl Cy3@MNPs by HepG2 and HeLa cells are investigated using confocal microscopy. The confocal images show that galactosyl Cy3@MNPs are sprayed over cytoplasm of the HepG2 cells, indicating that the MNP uptake occurs via receptor‐mediated endocytosis that is followed by release from endosomes. The results also reveal that the ligand spatial orientation affects the efficiency of the receptor‐mediated endocytosis and one of the tri‐antennary galactosyl ligands shows the best uptake efficiency owing to the optimal spatial presentation of the galactosyl moieties. Overall, it is shown that the MNP is a good ligand carrier and that, when pre‐assembled, the multivalent ligand structure enhances the interactions between the surface ligands of the MNPs and receptors of HepG2 cells. Additionally, the galactosyl Cy3@MNPs are not cytotoxic, indicating that they may potentially be used for in vivo applications.

Synthesis of 6-PEtN-α-D-GalpNAc-(1->6)-β-D-Galp-(1->4)-β-D-GlcpNAc-(1->3)-β-D-Galp-(1->4)-β-D-Glcp, a Haemophilus influenzae lipopolysacharide structure, and biotin and protein conjugates thereof.

Background: In bacteria with truncated lipopolysaccharide structures, i.e., lacking the O-antigen polysaccharide part, core structures are exposed to the immune system upon infection and thus their use as carbohydrate surface antigens in glycoconjugate vaccines can be considered and investigated. One such suggested structure from Haemophilus influenzae LPS is the phosphorylated pentasaccharide 6-PEtN-α-D-GalpNAc-(1→6)-β-D-Galp-(1→4)-β-D-GlcpNAc-(1→3)-β-D-Galp-(1→4)-β-D-Glcp.Results: Starting from a spacer-containing lactose derivative a suitably protected lacto-N-neotetraose tetrasaccharide structure was constructed through subsequential couplings with two thioglycoside donors, a glucosamine residue followed by a galactose derivative, using NIS/AgOTf as promoter. Removal of a silyl protecting group at the primary position of the non-reducing end residue afforded an acceptor to which the terminal α-galactosamine moiety was introduced using a 2-azido bromo sugar and halide assisted coupling conditions. Global deprotection afforded the non-phosphorylated target pentasaccharide, whereas removal of a silyl group from the primary position of the non-reducing end residue produced a free hydroxy group which was phosphorylated using H-phosphonate chemistry to yield the phosphoethanolamine-containing protected pentasaccharide. Partial deprotection afforded the phosphorylated target pentasaccharide with a free spacer amino group but with a protected phosphoethanolamino group. Conjugation of the spacer amino group to biotin or dimethyl squarate followed by deprotection of the phosphoethanolamino group and, in the case of the squarate derivative, further reaction with a protein then afforded the title conjugates.Conclusion: An effective synthesis of a biologically interesting pentasaccharide structure has been accomplished. The target pentasaccharide, an α-GalNAc substituted lacto-N-neotetraose structure, comprises a phosphoethanolamine motif and a spacer aglycon. Through the spacer, biotin and protein conjugates of the title compound have been constructed to allow further use in biological experiments.

Assessing the ability of a short fluorinated antifreeze glycopeptide and a fluorinated carbohydrate derivative to inhibit ice recrystallization

A short fluorinated antifreeze glycopeptide ( 2) was synthesized and evaluated for ice recrystallization inhibition (IRI) activity. The activity of 2 was compared to native biological antifreeze AFGP 8 and a rationally designed C-linked AFGP analogue (OGG-Gal, 1). In addition, a simple fluorinated galactose derivative was prepared and its IRI activity was compared to non-fluorinated compounds. The results from this study suggest that the stereochemistry at the anomeric position in the carbohydrate plays a role in imparting ice recrystallization inhibition activity and that incorporation of hydrophobic groups such as fluorine atoms cause a decrease in IRI activity. These observations are consistent with the theory that fluorine atoms increase ordering of bulk water resulting in a decrease of IRI activity, supporting our previously proposed mechanism of ice recrystallization inhibition.

‘Click chemistry’ synthesis of a library of 1,2,3-triazole-substituted galactose derivatives and their evaluation against Trypanosoma cruzi and its cell surface trans-sialidase

Trypanosoma cruzi trans-sialidase (TcTS) plays a key role in the recognition and invasion of host cells and in enabling the parasite to escape the human immune response. To explore this potential drug target, we have synthesized a small library of substrate analogues based on 1,4-disubstituted 1,2,3-triazole derivatives of galactose modified at either the C-1 or C-6 positions. This was achieved by coupling the appropriate azido-sugars with a panel of 23 structurally diverse terminal alkynes by using the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, giving a library of 46 derivatives in good to excellent yield and with complete regioselectivity. The sugar triazoles showed weak inhibition towards TcTS-catalyzed hydrolysis of 2′-(4-methylumbelliferyl)-α-d-N-acetylneuraminic acid in vitro (<40% inhibition at 1mM concentration); many of the compounds assessed proved to be acceptor substrates for the enzyme. Despite this modest inhibitory activity, in vitro trypanocidal activity assays against the trypomastigote form of T. cruzi Y strain revealed several compounds active in the low 100s of μM range. Further assessment of these compounds against cultured mouse spleen cells suggests a specific mode of anti-parasite action rather than a generic cytotoxic effect.

Lipoic acid glyco-conjugates, a new class of agents for controlling nonspecific adsorption of blood serum at biointerfaces for biosensor and biomedical applications.

The carbohydrate-derived lipoic acid derivatives were studied as protein and cell resistant biomaterials. Six types of carbohydrates were examined for their abilities to reduce nonspecific adsorption of human serum and Hela cell using quartz crystal microbalance. Our data suggested that the structures of carbohydrates play an important role in resisting nonspecific binding. Specifically, the resistance was found to increase in the order lipoic fucose < lipoic mannose < lipoic N-acetyl glucosamine < lipoic glucose < lipoic sialic acid < lipoic galactose, where lipoic galactose derivative resisted most nonspecific adsorption. Furthermore, the combination of lipoic galactose and BSA was the most effective in reducing the adsorption of even undiluted human serum and the attachment of Hela cells while allowing specific binding. Several control experiments have demonstrated that the resistant-ability of mixed lipoic galactose and BSA was comparable to the best known system for decreasing nonspecific adsorption.

Multiple and Regioselective Introduction of Protected Sulfates into Carbohydrates Using Sulfuryl Imidazolium Salts

Selective incorporation of trichloroethyl (TCE)-protected sulfates into monosaccharides was examined using reagent 2. In general, sulfation of 4,6-O-benzylidene acetals of galactosides and glucosides (2-OH versus 3-OH sulfations) proceeded in good to excellent yield and selectivity. Sulfation occurred predominantly at the 2-OH in 4,6-O-benzylidene acetals of alpha-glucosides and at the 3-OH in 4,6-O-benzylidene acetals of beta-galactosides and beta-glucosides. Good yields and selectivity was also achieved for the 3-OH in 3,4-diols of glucosides and galactosides. A glucoside bearing a 2-amino moiety and 6-OH group gave mainly the N-sulfated product in good yield. Selective sulfation of the primary 6-OH in galactose and glucose derivatives bearing one or two free secondary hydroxyl groups was also achieved usually in good yield and selectivity. Reagent 2 was also effective for the direct disulfation of diols of glucosides and galactosides, and trisulfated monosaccharides could be prepared from the disulfated compounds.

Efficient Stereoselective Glycosylations of Alcohols by Sugar Perpivalates: The First Use of 1-O-Pivaloylated Glycosyl Donors

1-O-Pivaloyl glycosides were shown to be efficient glycosyl donors by using the perpivaloylated derivatives of lactose, galactose and glucose in the direct ZnCl2-promoted glycosylations of various alcohols. The corresponding glycosides were isolated in good yields and β-selectivity.

Synthesis of Novel gluco‐ and galacto‐Functionalized Platinum Complexes

AbstractCisplatin, carboplatin, oxaliplatin and further derivatives are worldwide established cytostatics for the treatment of a vast range of tumours. These drugs showed extraordinary success; however, side effects and primary or developed secondary resistance of tumour cells represent severe problems, which prompt the development of novel functionalized platinum complexes. Selectively protected monohydroxy derivatives of glucose and galactose could be etherified by ω‐halo ethers. Further, Finkelstein reaction and malonate synthesis gave precursor glycoconjugates which were easily transformed into their (diammine)platinum complexes. First tests with different tumour cell lines show biological activity of the gluco‐functionalized platinum complex.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

Stereocontrolled Formation of Protected Aminodeoxyalditols from Simple Carbohydrate Precursors by Debenzylating Cycloetherification

A new and highly efficient methodology for the stereo-controlled synthesis of aminodeoxyalditols is described through a dimesylation/intramolecular S N 2 nucleophilic substitution ring-forming reaction sequence from glucose, mannose, and galactose derivatives. The degree of difficulty and rate of the reaction of dimesylates in the cyclization process is evaluated and shows the trend: galactose > glucose > mannose derivatives, which has been identified from our experiments and classical theories.

Hydration IndexA Better Parameter for Explaining Small Molecule Hydration in Inhibition of Ice Recrystallization

Several simple mono- and disaccharides have been assessed for their ability to inhibit ice recrystallization. Two carbohydrates were found to be effective recrystallization inhibitors. D-galactose (1) was the best monosaccharide and D-melibiose (5) was the most active disaccharide. The ability of each carbohydrate to inhibit ice growth was correlated to its respective hydration number reported in the literature. A hydration number reflects the number of tightly bound water molecules to the carbohydrate and is a function of carbohydrate stereochemistry. It was discovered that using the absolute hydration number of a carbohydrate does not allow one to accurately predict its ability to inhibit ice recrystallization. Consequently, we have defined a hydration index in which the hydration number is divided by the molar volume of the carbohydrate. This new parameter not only takes into account the number of water molecules tightly bound to a carbohydrate but also the size or volume of a particular solute and ultimately the concentration of hydrated water molecules. The hydration index of both mono- and disaccharides correlates well with experimentally measured RI activity. C-Linked derivatives of the monosaccharides appear to have RI activity comparable to that of their O-linked saccharides but a more thorough investigation is required. The relationship between carbohydrate concentration and RI activity was shown to be noncolligative and a 0.022 M solution of D-galactose (1) and C-linked galactose derivative (10) inhibited recrystallization as well as a 3% DMSO solution. The carbohydrates examined in this study did not possess any thermal hysteresis activity (selective depression of freezing point relative to melting point) or dynamic ice shaping. As such, we propose that they are inhibiting recrystallization at the interface between bulk water and the quasi liquid layer (a semiordered interface between ice and bulk water) by disrupting the preordering of water.

Comparative Positron-Emission Tomography (PET) Imaging and Phototherapeutic Potential of 124I- Labeled Methyl- 3-(1′-iodobenzyloxyethyl)pyropheophorbide-a vs the Corresponding Glucose and Galactose Conjugates

In our present study, 3-(1(')-m-iodobenzyloxyethyl)pyropheophorbide-a methyl ester 1, 3-(1'-m-iodobenzyloxyethyl)-17(2)-{(2-deoxy)glucose}pyropheophorbide-a 2, and 3-(1'-m-iodobenzyloxyethyl)-17(2)-{(1-deoxy)galactose}pyropheophorbide-a 3 were synthesized and converted into the corresponding (124)I-labeled analogues by reacting the intermediate trimethyltin analogues with Na(124)I. Photosensitizers 1-3 were evaluated for the PDT efficacy in C3H mice bearing RIF tumors at variable doses and showed a significant long-term tumor cure. Among the compounds investigated, the non-carbohydrate analogue 1 was most effective. These results were in contrast to the in vitro data, where compared to the parent analogue the corresponding galactose and glucose derivatives showed enhanced cell kill. Among the corresponding (124)I-labeled analogues, excellent tumor images were obtained from compound 1 in both tumor models (RIF and Colon-26) and the best tumor contrast was observed at 72 h after injection. Conjugating a glucose moiety to photosensitizer 1 initially diminished its tumor uptake, whereas with time the corresponding galactose analogue showed improved tumor contrast.

Oxidation of methyl α- d-galactopyranoside by galactose oxidase: products formed and optimization of reaction conditions for production of aldehyde

The reaction conditions of galactose oxidase-catalyzed, targeted C-6 oxidation of galactose derivatives were optimized for aldehyde production and to minimize the formation of secondary products. Galactose oxidase, produced in transgenic Pichia pastoris carrying the galactose oxidase gene from Fusarium spp., was used as catalyst, methyl α- d-galactopyranoside as substrate, and reaction medium, temperature, concentration, and combinations of galactose oxidase, catalase, and horseradish peroxidase were used as variables. The reactions were followed by 1H NMR spectroscopy and the main products isolated, characterized, and identified. An optimal combination of all the three enzymes gave aldehyde (methyl α- d-galacto-hexodialdo-1,5-pyranoside) in approximately 90% yield with a substrate concentration of 70 mM in water at 4 °C using air as oxygen source. Oxygen flushing of the reaction mixture was not necessary. The aldehyde existed as a hydrate in water. The main secondary products, a uronic acid (methyl α- d-galactopyranosiduronic acid) and an α,β-unsaturated aldehyde (methyl 4-deoxy-α- d- threo-hex-4-enodialdo-1,5-pyranoside), were observed for the first time to form in parallel. Formation of uronic acid seemed to be the result of impurities in the galactose oxidase preparation. 1H and 13C NMR data of the products are reported for the α,β-unsaturated aldehyde for the first time, and chemical shifts in DMSO- d 6 for all the products for the first time. Oxidation of d-raffinose (α- d-galactopyranosyl-(1-6)-α- d-glucopyranosyl-(1-2)-β- d-fructofuranoside) in the same optimum conditions also proceeded well, resulting in approximately 90% yield of the corresponding aldehyde.

Separation and quantification of component monosaccharides of the tea polysaccharides from Gynostemma pentaphyllum by HPLC with indirect UV detection

A reversed-phase high-performance liquid chromatographic (HPLC) method is described for the simultaneous determination of aldoses and uronic acids. The separation was carried out on a RP-C 18 column (4.6 mm i.d. × 250 mm, 5 μm, Venusil, USA) using precolumn derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) and UV detection at 250 nm, and the 10 PMP derivatives of mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose, arabinose and fucose were baseline separated within 40 min. Furthermore, the described method was applied to the quantitative analysis of component monosaccharides in the water-soluble polysaccharides extracted from Gynostemma pentaphyllum Makino tea and the result showed that the tea polysaccharide was a typical heteropolysaccharide and consisted of mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose and arabinose in the molar contents of 16.3, 10.3, 47.1, 5.6, 24.0, 128.4, 25.0, 101.4 and 71.1 μM, respectively. Quantitative recoveries of the component monosaccharides in the tea polysaccharide were in the range of 94.6–108.0% and the RSD values were lower than 4.9%. The results demonstrated that the proposed HPLC method was precise and practical for the analysis of the G. pentaphyllum tea polysaccharide.

Efficient Synthesis of a Sialic Acid α(2→3)Galactose Building Block and Its Application to the Synthesis of Ganglioside GM3

Glycosylation of various galactose derivatives with O-acetylated sialic acid N-phenyltrifluoroacetimidate as the donor was investigated. Efficient alpha(2,3)sialylation of galactose, with up to 73% yield and 8.4:1 stereoselectivity, was realized when 2,3,4-unprotected galactose derivatives and TBSOTf were used as acceptors and promoter, respectively. Sialylation of 2-(trimethylsilyl)ethyl 6-O-tert-butyldiphenylsilyl-beta-D-galactopyranoside (3f) gave the best result, and the resultant Neu5Ac alpha(2-->3)Gal disaccharide was successfully used in the synthesis of ganglioside GM3.

Cross metathesis for the synthesis of novel C-sialosides

Cross metathesis of both anomers of C-allyl sialoside ( 3α/ 3β) with styrene catalyzed by the second generation Grubbs or Hoveyda-Grubbs catalysts gave the corresponding aryl derivatives ( 4α/ 4β) in virtually quantitative yields. The products were hydrogenated to model compounds 5α/ 5β. Similarly, reaction of the α-anomer 3α with galactose derivative 8 gave the olefin-linked disaccharide mimetic 9. Following hydrogenation and deprotection, the ethylene-bridged Neu5Acα(2→6)Gal analogue 11 could be obtained.