A Bisubstrate Analog Inhibitor for a(1→2)-FucosyItransferase

Discovery of novel FUT8 inhibitors with promising affinity and in vivo efficacy for colorectal cancer therapy

As a member of glycosyltransferases, fucosyltransferase 8 (FUT8) is essential to core fucosylation and has been considered as a potential therapeutic target for malignant tumors, including colorectal cancer (CRC). Based on the identification of key binding residues and probable conformation of FUT8, an integrated strategy that combines virtual screening and chemical optimization was carried out and compound 15 was identified as a potent FUT8 inhibitor with novel chemical structure and in vitro antitumor activity. Moreover, chemical pulldown experiments and binding assays confirmed that compound 15 selectively bound to FUT8. In vivo, compound 15 showed promising anti-CRC effects in SW480 xenografts. These data support that compound 15 is a potential FUT8 inhibitor for CRC treatment and deserve further optimization studies.

Therapeutic potential of fucosyltransferases in cancer and recent development of targeted inhibitors

Fucosyltransferases (FUTs) have significant roles in various pathophysiological events. Their high expression is a signature of malignant cell transformation, contributing to many abnormal events during cancer development, such as uncontrolled cell proliferation, tumor cell invasion, angiogenesis, metastasis, immune evasion, and therapy resistance. Therefore, FUTs have evolved as an attractive therapeutic target for treating solid cancers, and many substrate analogs have been discovered with potential as FUT inhibitors for cancer therapy. Meanwhile, the development of FUT protein structures represents a significant advance in the design of FUT inhibitors with nonsubstrate structures. In this review, we summarize the role of FUTs in cancers, the resolved protein crystal structures and progress in the development of FUT inhibitors as cancer therapeutics.

Chemical tools to explore nutrient-driven O-GlcNAc cycling

Posttranslational modifications (PTM) including glycosylation, phosphorylation, acetylation, methylation and ubiquitination dynamically alter the proteome. The evolutionarily conserved enzymes O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) and O-GlcNAcase are responsible for the addition and removal, respectively, of the nutrient-sensitive PTM of protein serine and threonine residues with O-GlcNAc. Indeed, the O-GlcNAc modification acts at every step in the "central dogma" of molecular biology and alters signaling pathways leading to amplified or blunted biological responses. The cellular roles of OGT and the dynamic PTM O-GlcNAc have been clarified with recently developed chemical tools including high-throughput assays, structural and mechanistic studies and potent enzyme inhibitors. These evolving chemical tools complement genetic and biochemical approaches for exposing the underlying biological information conferred by O-GlcNAc cycling.

Bisubstrate UDP-peptide conjugates as human O-GlcNAc transferase inhibitors

Inhibitors of OGT (O-GlcNAc transferase) are valuable tools to study the cell biology of protein O-GlcNAcylation. We report OGT bisubstrate-linked inhibitors (goblins) in which the acceptor serine in the peptide VTPVSTA is covalently linked to UDP, eliminating the GlcNAc pyranoside ring. Goblin1 co-crystallizes with OGT, revealing an ordered C₃ linker and retained substrate-binding modes, and binds the enzyme with micromolar affinity, inhibiting glycosyltransfer on to protein and peptide substrates.

Inhibitors of OGT (O-GlcNAc transferase) are valuable tools to study the cell biology of protein O-GlcNAcylation. We report OGT bisubstrate-linked inhibitors (goblins) in which the acceptor serine in the peptide VTPVSTA is covalently linked to UDP, inhibiting glycosyltransfer on to protein and peptide substrates.

Development of fucosyltransferase and fucosidase inhibitors

L-Fucose-containing glycoconjugates are essential for a myriad of physiological and pathological activities, such as inflammation, bacterial and viral infections, tumor metastasis, and genetic disorders. Fucosyltransferases and fucosidases, the main enzymes involved in the incorporation and cleavage of L-fucose residues, respectively, represent captivating targets for therapeutic treatment and diagnosis. We herein review the important breakthroughs in the development of fucosyltransferase and fucosidase inhibitors. To demonstrate how the synthesized small molecules interact with the target enzymes, i.e. delineation of the structure-activity relationship, we cover the reaction mechanisms and resolved X-ray crystal structures, discuss how this information guides the design of enzyme inhibitors, and explain how the molecules were optimized to achieve satisfying potency and selectivity.

Development of inhibitors as research tools for carbohydrate-processing enzymes

Carbohydrates, which are present in all domains of life, play important roles in a host of cellular processes. These ubiquitous biomolecules form highly diverse and often complex glycan structures without the aid of a template. The carbohydrate structures are regulated solely by the location and specificity of the enzymes responsible for their synthesis and degradation. These enzymes, glycosyltransferases and glycoside hydrolases, need to be functionally well characterized in order to investigate the structure and function of glycans. The use of enzyme inhibitors, which target a particular enzyme, can significantly aid this understanding, and may also provide insights into therapeutic applications. The present article describes some of the approaches used to design and develop enzyme inhibitors as tools for investigating carbohydrate-processing enzymes.

Multisubstrate adduct inhibitors: drug design and biological tools

In drug discovery, different methods exist to create new inhibitors possessing satisfactory biological activity. The multisubstrate adduct inhibitor (MAI) approach is one of these methods, which consists of a covalent combination between analogs of the substrate and the cofactor or of the multiple substrates used by the target enzyme. Adopted as the first line of investigation for many enzymes, this method has brought insights into the enzymatic mechanism, structure, and inhibitory requirements. In this review, the MAI approach, applied to different classes of enzyme, is reported from the point of view of biological activity.

FRET-based direct and continuous monitoring of human fucosyltransferases activity: an efficient synthesis of versatile GDP-L-fucose derivatives from abundant D-galactose

We have developed a facile and versatile protocol for the continuous monitoring of human fucosyltransferases activity by using fluorescence energy resonance transfer (FRET), and have explored the feasibility of its use in an inhibitor screening assay. A convenient sugar nucleotide with a fluorogenic probe, 6-deoxy-6-N-(2-naphalene-2-yl-acetamide)-beta-L-galactopyranos-1-yl-guanosine 5'-diphosphate disodium salt (1), was efficiently synthesized from naturally abundant D-galactopyranose via a key intermediate, 6-azide-1,2,3,4-tetra-O-benzoyl-6-deoxy-beta-L-galactopyranose (10). It was demonstrated that the combined use of the glycosyl donor 1 and a dansylated acceptor substrate, sialyl-alpha2,3-LacNAc derivative (2) allowed us to carry out highly sensitive, direct, and continuous in vitro monitoring of the generation of sialyl Lewis X (SLe x), which is catalyzed by human alpha-1,3-fucosyltransferase VI (FUT-VI). A kinetic analysis revealed that compound 1 was an excellent donor substrate (KM=0.94 microM and Vmax=0.14 microM min(-1)) for detecting human FUT-VI activity. To the best of our knowledge, this synthetic fluorogenic probe is the most sensitive and selective donor substrate for FUT-VI among all of the known GDP-Fuc analogues, including the parent GDP-Fuc. When a dansylated asparagine-linked glycopeptide 20, which is derived from egg yolk was employed as an alternate acceptor substrate, a FRET-based assay with compound 1 could be used to directly monitor the alpha1,6-fucosylation at the reducing terminal GlcNAc residue by human FUT-VIII (KM=175 microM and Vmax=0.06 microM/ min); this indicates that the present method might become a general protocol for the characterization of various mammalian fucosyltransferases in the presence of designated fluorogenic acceptor substrates. The present protocol revealed that compound 23, which was obtained by a 1,3-dipolar cycloaddition between the disodium salt 16 and 1-ethynyl-naphthalene exhibits highly potent inhibitory effects against the FUT-VI-mediated sialyl Lewis X synthesis (IC50=5.4 microM).

Glycan antagonists and inhibitors: a fount for drug discovery

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

Non-isosteric C-glycosyl analogues of natural nucleotide diphosphate sugars as glycosyltransferase inhibitors

A series of C-glycosyl ethylphosphonophosphate analogues of UDP-Glc, UDP-Gal, UDP-GlcNAc and GDP-Fuc were synthesized from the corresponding C-glycosyl ethylphosphonic acids. Analogues were obtained as alpha-anomers through either diastereoselective photo-induced radical addition of glycosyl bromides (D-Glc, D-Gal and L-Fuc) to diethyl vinylphosphonate, or a multi-step sequence (D-GlcNAc), with subsequent coupling with morpholidate-activated nucleotide monophosphates. The in vitro inhibitory activity of UDP-Gal, GDP-Fuc and UDP-GlcNAc analogues towards glycosyltransferases (beta-1,4-GalT, FUT3 and LgtA) was evaluated through a competition fluorescence assay and IC(50) values of 40 microM, 2 mM and 3.5 mM were obtained, respectively.

Spirocyclopropyl pyrrolidines as a new series of α-l-fucosidase inhibitors

Polyhydroxy 4-azaspiro[2.4]heptane derivatives (spirocyclopropyl iminosugars) were prepared in four to six steps from readily available protected aldoses. The key step of the reaction sequence involves a titanium-mediated aminocyclopropanation of glycononitriles with subsequent cyclization. Five new polyhydroxypyrrolidines so-obtained have been evaluated for their ability to inhibit 16 glycosidases. One of them exhibits selective inhibition of alpha-L-fucosidase from bovine kidney (Ki=1.6 microM, competitive).

Systematic Synthesis of Bisubstrate-Type Inhibitors ofN-Acetylglucosaminyltransferases

Bisubstrate-type inhibitors for N-acetylglucosaminyltransferase (GnT)-V and -IX were designed and synthesized. These compounds carry both an acceptor trisaccaride and an UDP-GlcNAc component tethered by a linker of variable length. The acceptor trisaccharide unit was constructed using a combination of a polymer support and a resin capture-release strategy. Namely, starting with a beta-mannoside bound to low molecular weight monomethyl PEG (MPEG), successive glycosylations with donors having chloroacetyl group produced the trisaccharide, which was subjected to the capture-release purification using cysteine loaded resin. UDP-GlcNAc units carrying phosphate moieties were separately synthesized from the bromoacetamide-containing glucosamine derivative. Ligation between the acceptor thiol and each alkyl bromide on the donor unit readily proceeded, and produced the coupling product. The introduction of the UMP component gave target compounds. All of the synthesized compounds had significant activities to GnT-V and -IX. Their potencies were dependent upon the linkers length. GnT-IX was more sensitive to these inhibitors and optimum linker length was clearly different between these GnTs. The most potent inhibitor of GnT-V had Ki=18.3 microM, while that of GnT-IX had Ki = 4.7 microM.

Synthesis of bisubstrate analogues targeting α-1,3-fucosyltransferase and their activities

We designed two bisubstrate analogues targeting alpha-1,3-fucosyltransferases, based on the three dimensional structure of Lewis X, which is the product of a alpha-1,3-fucosyltransferase reaction. We selected guanosine-5'-diphospho-L-galactose as a donor mimic and 2-hydroxyethyl beta-D-galactoside as an acceptor mimic, and tethered these two mimics with a methylene or ethylene linker. For the synthesis, the 6-position of L-galactose and the 6-position of D-galactose were first tethered via a methylene or ethylene linker. The L-galactose moiety was then converted to a GDP derivative. Both bisubstrate analogues were moderate inhibitors against alpha-1,3-fucosyltransferase V and VI. The fact that they were substrates of alpha-1,3-fucosyltransferase VI suggested that these compounds bound to the donor binding site, but not to the acceptor binding site.

Rational design, synthesis, and characterization of novel inhibitors for human beta1,4-galactosyltransferase

An affinity labeling reagent, uridine 5'-(6-amino-{2-[(7-bromomethyl-2-naphthyl)methoxycarbonylmethoxy]ethoxy}acetyl-6-deoxy-alpha-D-galactopyranosyl) diphosphate (1a), was designed on the basis of 3D docking simulation and synthesized to investigate the functional role of Trp310 residue located in the small loop near the active site of human recombinant galactosyltransferase (betaGalT-1). Mass spectrometric analysis revealed that the Trp310 residue of betaGalT1 can be selectively modified with the naphthylmethyl group of compound 1a at the C-3 position of the indole ring. This result motivated us to synthesize novel uridine-5'-diphosphogalactose (UDP-Gal) analogues as candidates for mechanism-based inhibitors for betaGalT-1. We found that uridine 5'-(6-O-[10-(2-naphthyl)-3,6,9-trioxadecanyl]-alpha-d-galactopyranosyl) diphosphate (2) is the strongest inhibitor (K(i) = 1.86 microM) against UDP-Gal (Km = 4.91 microM) among compounds reported previously. A cold spray ionization time-of-flight mass spectrometry study demonstrated that the complex of this inhibitor and betaGalT-1 cannot interact with an acceptor substrate in the presence of Mn2+.

Synthesis of Bisubstrate and Donor Analogues of Sialyltransferase and Their Inhibitory Activities

[reaction: see text] Sialyltransferases (STs) are involved in the biosynthesis of glycoconjugates with important biological activities. Most STs utilize cytidine-5'-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac) as a common donor substrate. A bisubstrate analogue containing the donor substrate (CMP-Neu5Ac mimic) and the acceptor substrate (galactose) was synthesized. Four donor analogues having the partial structure of the bisubstrate analogue were also synthesized to support study of the structure-activity relationship. Each analogue contains an ethylene group in place of the exocyclic anomeric oxygen of CMP-Neu5Ac. The bisubstrate analogue exhibited only weak inhibitory activity to rat recombinant alpha-2,3- and alpha-2,6-ST (IC(50) = 1.3, 2.4 mM). Conversion of the C-1 carboxylate of the Neu5Ac moiety to carboxyamide, hydroxymethyl, or methylene phosphate each resulted in a reduction in inhibitory activity. Among the synthesized analogues, cytidin-5'-yl sialylethylphosphonate (4) was the most potent inhibitor against rat recombinant alpha-2,3- and alpha-2,6-ST (IC(50) = 0.047, 0.34 mM).

Systematic syntheses and inhibitory activities of bisubstrate-type inhibitors of sialyltransferases

Bisubstrate-type sialyltransferase inhibitors 1/2a-e, having CMP-NeuAc and N-acetyllactosamine (or lactose) moieties connected by an alkanedithiol linker, were synthesized systematically. A uniform synthetic strategy was adopted that consists of consecutive couplings of three components (N-acetyllactosamine or lactose, sialic acid, and CMP), followed by oxidation. Due to the sensitivity of the compounds under alkaline conditions, final deprotection required careful monitoring by (1)H NMR. The inhibitory activities of 1/2a-e toward ST6N and ST3N indicated that both the structure of the acceptor moiety and the distance between donor and acceptor moieties were important.

Synthesis and biological evaluation of new UDP-GalNAc analogues for the study of polypeptide-alpha-GalNAc-transferases

A series of three O-methylated UDP-GalNAc analogues have been synthesised using a divergent strategy from a 3,6-di-O-pivaloyl GlcNAc derivative. The biological activity of these probes toward polypeptide-alpha-GalNAc-transferase T1 has been investigated. This study shows that this glycosyltransferase exhibits a very high substrate specificity.

The Hexapeptide inhibitor of Galbeta 1,3GalNAc-specific alpha 2,3-sialyltransferase as a generic inhibitor of sialyltransferases

The mammalian Galbeta1,3GalNAc-specific alpha2,3-sialyltransferase (ST3Gal I) was expressed as a secreted glycoprotein in High Five (Trichoplusia ni) cells. Using this recombinant ST3Gal I, we screened the synthetic hexapeptide combinatorial library to explore a sialyltransferase inhibitor. We found that the hexapeptide, NH(2)-GNWWWW, exhibited the most strong inhibition of ST3Gal I among five different hexapeptides that were finally selected. The kinetic analysis of ST3Gal I inhibition demonstrated that this hexapeptide could act as a competitive inhibitor (K(i) = 1.1 microm) on CMP-NeuAc binding to the enzyme. Moreover, the hexapeptide was shown to strongly inhibit both N-glycan-specific alpha2,3- and alpha2,6-sialyltranferase in vitro, suggesting that this peptide may inhibit the broad range of sialyltransferases regardless of their linkage specificity. The inhibitory activity in vivo was investigated by RCA-I lectin blot analyses and by metabolic d-[6-(3)H]GlcNH(2) radiolabeling analyses of N- and O-linked oligosaccharides in Chines hamster ovary cells. Our results demonstrate that the hexapeptide can act as a generic inhibitor of the N- and O-glycan-specific sialyltransferases in mammalian cells, which results in the significantly reduced NeuAc expression on cellular glycoproteins in vivo.

Synthesis of [(2S,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-5-methylfuran-4-carboxylic acid derivatives: new leads as selective beta-galactosidase inhibitors

The preparation of [(2S,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]furan derivatives in a stereoselective route starting from D-glucose and ethyl acetoacetate is presented. Ethyl ester (6), N,N-diethylamide (7) and N-isopropylamide (8) have been tested towards 25 glycosidases. Ester (6) is a selective inhibitor of beta-galactosidases. The new compounds represent a new type of imino-C-nucleoside analogues.

Intrinsic lipid preferences and kinetic mechanism of Escherichia coli MurG

MurG, the last enzyme involved in the intracellular phase of peptidoglycan synthesis, is a membrane-associated glycosyltransferase that couples N-acetyl glucosamine to the C4 hydroxyl of a lipid-linked N-acetyl muramic acid derivative (lipid I) to form the beta-linked disaccharide (lipid II) that is the minimal subunit of peptidoglycan. Lipid I is anchored to the bacterial membrane by a 55 carbon undecaprenyl chain. Because this long lipid chain impedes kinetic analysis of MurG, we have been investigating alternative substrates containing shortened lipid chains. We now describe the intrinsic lipid preferences of MurG and show that the optimal substrate for MurG in the absence of membranes is not the natural substrate. Thus, while the undecaprenyl carrier lipid may be critical for certain steps in the biosynthetic pathway to peptidoglycan, it is not required-in fact, is not preferred-by MurG. Using synthetic substrate analogues and products containing different length lipid chains, as well as a synthetic dead-end acceptor analogue, we have also shown that MurG follows a compulsory ordered Bi Bi mechanism in which the donor sugar binds first. This information should facilitate obtaining crystals of MurG with substrates bound, an important goal because MurG belongs to a major superfamily of NDP-glycosyltransferases for which no structures containing intact substrates have yet been solved.

SAR directed design and synthesis of novel beta(1-4)-glucosyltransferase inhibitors and their in vitro inhibition studies

This paper describes SAR directed design and synthesis of novel beta(1-4)-glucosyltransferase (BGT) inhibitors. The designed inhibitors 1-5 provide conformational mimicry of the transition-state in glucosyltransfer reactions. The compounds were tested for in vitro inhibitory activity against (BGT) and the inhibition kinetics were examined. Three of the designed molecules were found to be potential inhibitors of BGT having IC50 values in micromolar (microM) range. Useful structure-activity relationships were established, which provide guidelines for the design of future generations of inhibitors of BGT.

An inhibitor of the human UDP-GlcNAc 4-epimerase identified from a uridine-based library: a strategy to inhibit O-linked glycosylation

The biological study of O-linked glycosylation is particularly problematic, as chemical tools to control this modification are lacking. An inhibitor of the UDP-GlcNAc 4-epimerase that synthesizes UDP-GalNAc, the donor initiating O-linked glycosylation, would be a powerful reagent for reversibly inhibiting O-linked glycosylation. We synthesized a 1338 member library of uridine analogs directed to the epimerase by virtue of substrate mimicry. Screening of the library identified an inhibitor with a K(i) value of 11 microM. Tests against related enzymes confirmed the compound's specificity for the UDP-GlcNAc 4-epimerase. Inhibitors of a key step of O-linked glycan biosynthesis can be discovered from a directed library screen. Progeny thereof may be powerful tools for controlling O-linked glycosylation in cells.

Synthesis and evaluation of a C-glycosyl nucleoside as an inhibitor of chitin synthase

As part of our ongoing program devoted to inhibit chitin synthases, we have prepared a novel C-glycosyl nucleoside as metabolically stable substrate analog of UDP-GlcNAc. The synthetic strategy relies on the consecutive coupling of nucleoside and amino C-glycosyl moieties with L-tartaric acid. However, this compound inhibited only weakly chitin synthase I, with an IC(50) value of 20 mM.

Inhibition of fucosyltransferase V by a GDP-Azasugar

A GDP-azasugar conjugate was synthesized starting from an enzymatically obtained phosphorylated azasugar. It inhibits human fucosyltransferase V at micromolar concentrations, which is discussed in terms of transition state analogy.

Synthetic mannosides act as acceptors for mycobacterial α1-6 mannosyltransferase

A series of synthetic mannosides was screened in a cell-free system for their ability to act as acceptor substrates for mycobacterial mannosyltransferases. Evaluation of these compounds demonstrated the incorporation of [14C]Man from GDP-[14C]Man into a radiolabeled organic-soluble fraction and analysis by thin layer chromatography and autoradiography revealed the formation of two radiolabeled products. Each synthetic acceptor was capable of accepting one or two mannose residues, resulting in a major and a minor mannosylated product. Both products from each acceptor were isolated and their mass was confirmed by fast-atom bombardment-mass spectrometry (FABMS). Characterization of each mannosylated product by exo-glycosidase digestion. acetolysis and linkage analysis by gas chromatography mass spectrometry of partially per-O-methylated alditols, revealed only alpha1-6-linked products. In addition. the antibiotic amphomycin selectively inhibited the formation of mannosylated products suggesting polyprenolmonophosphate-mannose (C15 50-P-Man) was the immediate mannose donor in all mannosylation reactions observed. The ability of synthetic disaccharides to act as acceptor substrates in this system, is most likely due to the action of a mycobacterial polyprenol-P-Man:mannan alpha1-6 mannosyltransferase involved in the biosynthesis of linear alpha1-6-linked lipomannan.

Chemo-enzymatic synthesis of fluorinated sugar nucleotide: useful mechanistic probes for glycosyltransferases

An effective procedure for the synthesis of 2-deoxy-2-fluoro-sugar nucleotides via Select fluor-mediated electrophilic fluorination of glycals with concurrent nucleophilic addition or chemo-enzymatic transformation has been developed, and the fluorinated sugar nucleotides have been used as probes for glycosyltransferases, including fucosyltransferase III, V, VI, and VII, and sialyl transferases. In general, these fluorinated sugar nucleotides act as competitive inhibitors versus sugar nucleotide substrates and form a tight complex with the glycosyltransferase.

The C-disaccharide alpha-C(1-->3)-mannopyranoside of N-acetylgalactosamine is an inhibitor of glycohydrolases and of human alpha-1,3-fucosyltransferase VI. Its epimer alpha-(1-->3)-mannopyranoside of N-acetyltalosamine is not

The radical C-glycosidation of (-)-(1S,4R,5R, 6R)-6-endo-chloro-3-methylidene-5-exo-(phenylseleno)-7-ox abi cyclo[2. 2.1]heptan-2-one ((-)-4) with 2,3,4, 6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide gave (+)-(1S,3R,4R, 5R,6R)-6-endo-chloro-5-exo-(phenylseleno)-3-endo-(1',3',4', 5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-7-oxabi cyc lo[ 2.2.1]hept-2-one ((+)-5) that was converted into (+)-(1R,2S,5R, 6R)-5-acetamido-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl)-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-10) and into (+)-(1R,2S,5R, 6S)-5-bromo-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-19). Ozonolysis of (+)-10 and further transformations provided 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-galac tos e (alpha-C(1-->3)-D-mannopyranoside of N-acetylgalactosamine (alpha-D-Manp-(1-->3)CH(2)-D-GalNAc): 1). Displacement of the bromide (+)-19 with NaN(3) in DMF provided the corresponding azide ((-)-20) following a S(N)2 mechanism. Ozonolysis of (-)-20 and further transformations led to 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-talose (alpha-C(1-->3)-D-mannopyranoside of N-acetyl D-talosamine (alpha-D-Manp-(1-->3)CH(2)-D-TalNAc): 2). The neutral C-disaccharide 1 inhibits several glycosidases (e.g., beta-galactosidase from jack bean with K(i) = 7.5 microM, alpha-L-fucosidase from human placenta with K(i) = 28 microM, beta-glucosidase from Caldocellum saccharolyticum with K(i) = 18 microM) and human alpha-1, 3-fucosyltransferase VI (Fuc-TVI) with K(i) = 120 microM whereas it 2-epimer 2 does not. Double reciprocal analysis showed that the inhibition of Fuc-TVI by 1 displays a mixed pattern with respect to both the donor sugar GDP-fucose and the acceptor LacNAc with K(i) of 123 and 128 microM, respectively.

Synthesis and enzymatic evaluation of modified acceptors of recombinant blood group A and B glycosyltransferases

The disaccharide alpha-L-Fucp-(1 --> 2)-beta-D-Galp-(1 --> O)-Octyl (1) is an acceptor for the human blood group A and B glycosyltransferases. Seven analogues of 1, containing deoxy, methoxy and arabino modifications of the Fuc residue, were chemically synthesized and kinetically evaluated in radioactive enzymatic assays. Both the enzymes tolerate modification of the 3'-OH on the fucose residue. The 2'-OH was found to be key to the recognition of the acceptors by these enzymes. The arabino derivative was recognized as an acceptor by the A transferase (Km of 200 microM), but not the B transferase and is the first synthetic acceptor capable of distinguishing between the two enzyme activities.

alpha1,3Fucosyltransferase VI is expressed in HepG2 cells and codistributed with beta1,4galactosyltransferase I in the golgi apparatus and monensin-induced swollen vesicles

The major alpha1,3fucosyltransferase activity in plasma, liver, and kidney is related to fucosyltransferase VI which is encoded by the FUT6 gene. Here we demonstrate the presence of alpha1, 3fucosyltransferase VI (alpha3-FucT VI) in the human HepG2 hepatoma cell line by specific activity assays, detection of transcripts, and the use of specific antibodies. First, FucT activity in HepG2 cell lysates was shown to prefer sialyl-N-acetyllactosamine as acceptor substrate indicating expression of alpha3-FucT VI. RT-PCR analysis further confirmed the exclusive presence of the alpha3-FucT VI transcripts among the five human alpha3-FucTs cloned to date. alpha3-FucT VI was colocalized with beta1,4galactosyltransferase I (beta4-GalT I) to the Golgi apparatus by dual confocal immunostaining. Pulse/chase analysis of metabolically labeled alpha3-FucT VI showed maturation of alpha3-FucT VI from the early 43 kDa form to the mature, endoglycosidase H-resistant form of 47 kDa which was detected after 2 h of chase. alpha3-FucT VI was released to the medium and accounted for 50% of overall cell-associated and released enzyme activity. Release occurred by proteolytical cleavage which produced a soluble form of 43 kDa. Monensin treatment segregated alpha3-FucT VI from the Golgi apparatus to swollen peripheral vesicles where it was colocalized with beta4-GalT I while alpha2,6(N)sialyltransferase remained associated with the Golgi apparatus. Both constitutive secretion of alpha3-FucT VI and its monensin-induced relocation to vesicles analogous to beta4-GalT I suggest a similar post-Golgi pathway of both alpha3-FucT VI and beta4-GalT I.