Synergistic Inhibition of Human α-1,3-Fucosyltransferase V

Preference of Bacterial Rhamnosyltransferases for 6-Deoxysugars Reveals a Strategy To Deplete O-Antigens

Bacteria synthesize hundreds of bacteria-specific or "rare" sugars that are absent in mammalian cells and enriched in 6-deoxy monosaccharides such as l-rhamnose (l-Rha). Across bacteria, l-Rha is incorporated into glycans by rhamnosyltransferases (RTs) that couple nucleotide sugar substrates (donors) to target biomolecules (acceptors). Since l-Rha is required for the biosynthesis of bacterial glycans involved in survival or host infection, RTs represent potential antibiotic or antivirulence targets. However, purified RTs and their unique bacterial sugar substrates have been difficult to obtain. Here, we use synthetic nucleotide rare sugar and glycolipid analogs to examine substrate recognition by three RTs that produce cell envelope components in diverse species, including a known pathogen. We find that bacterial RTs prefer pyrimidine nucleotide-linked 6-deoxysugars, not those containing a C6-hydroxyl, as donors. While glycolipid acceptors must contain a lipid, isoprenoid chain length, and stereochemistry can vary. Based on these observations, we demonstrate that a 6-deoxysugar transition state analog inhibits an RT in vitro and reduces levels of RT-dependent O-antigen polysaccharides in Gram-negative cells. As O-antigens are virulence factors, bacteria-specific sugar transferase inhibition represents a novel strategy to prevent bacterial infections.

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.

Iminosugars as glycosyltransferase inhibitors

Iminosugars are naturally occurring carbohydrate analogues known since 1967. These natural compounds and hundreds of their synthetic derivatives prepared over five decades have been mainly exploited to inhibit the glycosidases, the enzymes catalysing the glycosidic bond cleavage, in order to find new drugs for the treatment of type 2 diabetes and other diseases. However, iminosugars are also inhibitors of glycosyltransferases, the enzymes responsible for the synthesis of oligosaccharides and glycoconjugates. The selective inhibition of specific glycosyltransferases involved in cancer or bacterial infections could lead to innovative therapeutic agents. The synthesis and biological properties of all the iminosugars assayed to date as glycosyltransferase inhibitors are reviewed in the present article.

Inhibitory properties of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) derivatives acting on glycogen metabolising enzymes

Glycogen synthase (GS) and glycogen phosphorylase (GP) are the key enzymes that control, respectively, the synthesis and degradation of glycogen, a multi-branched glucose polymer that serves as a form of energy storage in bacteria, fungi and animals. An abnormal glycogen metabolism is associated with several human diseases. Thus, GS and GP constitute adequate pharmacological targets to modulate cellular glycogen levels by means of their selective inhibition. The compound 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) is a known potent inhibitor of GP. We studied the inhibitory effect of DAB, its enantiomer LAB, and 29 DAB derivatives on the activity of rat muscle glycogen phosphorylase (RMGP) and E. coli glycogen synthase (EcGS). The isoform 4 of sucrose synthase (SuSy4) from Solanum tuberosum L. was also included in the study for comparative purposes. Although these three enzymes possess highly conserved catalytic site architectures, the DAB derivatives analysed showed extremely diverse inhibitory potential. Subtle changes in the positions of crucial residues in their active sites are sufficient to discriminate among the structural differences of the tested inhibitors. For the two Leloir-type enzymes, EcGS and SuSy4, which use sugar nucleotides as donors, the inhibitory potency of the compounds analysed was synergistically enhanced by more than three orders of magnitude in the presence of ADP and UDP, respectively. Our results are consistent with a model in which these compounds bind to the subsite in the active centre of the enzymes that is normally occupied by the glucosyl residue which is transferred between donor and acceptor substrates. The ability to selectively inhibit the catalytic activity of the key enzymes of the glycogen metabolism may represent a new approach for the treatment of disorders of the glycogen metabolism.

Development of α1,6-fucosyltransferase inhibitors through the diversity-oriented syntheses of GDP-fucose mimics using the coupling between alkyne and sulfonyl azide

We developed α1,6-fucosyltransferase (FUT8) inhibitors through a diversity-oriented synthesis. The coupling reaction between the fucose unit containing alkyne and the guanine unit containing sulfonyl azide under various conditions afforded a series of Guanosine 5'-diphospho-β-l-fucose (GDP-fucose) analogs. The synthesized compounds displayed FUT8 inhibition activity. A docking study revealed that the binding mode of the inhibitor synthesized with FUT8 was similar to that of GDP-fucose.

Evaluation of monovalent and multivalent iminosugars to modulate Candida albicans β-1,2-mannosyltransferase activities

β-1,2-Linked oligomannosides substitute the cell wall of numerous yeast species. Several of those including Candida albicans may cause severe infections associated with high rates of morbidity and mortality, especially in immunocompromised patients. β-1,2-Mannosides are known to be involved in the pathogenic process and to elicit an immune response from the host. In C. albicans, the synthesis of β-mannosides is under the control of a family of nine genes coding for putative β-mannosyltransferases. Two of them, CaBmt1 and CaBmt3, have been shown to initiate and prime the elongation of the β-mannosides on the cell-wall mannan core. In the present study, we have assessed the modulating activities of monovalent and multivalent iminosugar analogs on these enzymes in order to control the enzymatic bio-synthesis of β-mannosides. We have identified a monovalent deoxynojirimycin (DNJ) derivative that inhibits the CaBmt1-catalyzed initiating activity, and mono-, tetra- and polyvalent deoxymannojirimycin (DMJ) that modulate the CaBmt1 activity toward the formation of a single major product. Analysis of the aggregating properties of the multivalent iminosugars showed their ability to elicit clusterization of both CaBmt1 and CaBmt3, without affecting their activity. These results suggest promising roles for multivalent iminosugars as controlling agents for the biosynthesis of β-1,2 mannosides and for monovalent DNJ derivative as a first target for the design of future β-mannosyltransferase inhibitors.

Concise syntheses of selective inhibitors against α-1,3-galactosyltransferase

Several iminosugar-based uridine diphosphate galactose (UDP-Gal) mimetics 1-4 including d- and l-epimers were designed and synthesized by concise routes, and these synthetic compounds were evaluated for the inhibition of α-1,3- and β-1,4-galactosyltransferases in vitro. The experimental data demonstrated that l-epimer 2 displayed the strongest inhibitory activity with moderate selectivity against α-1,3-galactosyltransferase.

Probing replacement of pyrophosphate via click chemistry; synthesis of UDP-sugar analogues as potential glycosyl transferase inhibitors

A series of potential UDP-sugar mimics were readily synthesised by copper(I) catalysed modified Huisgen cycloaddition of the corresponding alpha-propargyl glycosides with 5-azido uridine in aqueous solution. None of the compounds accessed displayed significant inhibitory activity at concentrations of up to 4.5mM in an assay against bovine milk beta-1,4-galactosyltransferase.

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).

Natural-product sugar biosynthesis and enzymatic glycodiversification

Many biologically active small-molecule natural products produced by microorganisms derive their activities from sugar substituents. Changing the structures of these sugars can have a profound impact on the biological properties of the parent compounds. This realization has inspired attempts to derivatize the sugar moieties of these natural products through exploitation of the sugar biosynthetic machinery. This approach requires an understanding of the biosynthetic pathway of each target sugar and detailed mechanistic knowledge of the key enzymes. Scientists have begun to unravel the biosynthetic logic behind the assembly of many glycosylated natural products and have found that a core set of enzyme activities is mixed and matched to synthesize the diverse sugar structures observed in nature. Remarkably, many of these sugar biosynthetic enzymes and glycosyltransferases also exhibit relaxed substrate specificity. The promiscuity of these enzymes has prompted efforts to modify the sugar structures and alter the glycosylation patterns of natural products through metabolic pathway engineering and enzymatic glycodiversification. In applied biomedical research, these studies will enable the development of new glycosylation tools and generate novel glycoforms of secondary metabolites with useful biological activity.

Unusual sugar biosynthesis and natural product glycodiversification

The enzymes involved in the biosynthesis of carbohydrates and the attachment of sugar units to biological acceptor molecules catalyse an array of chemical transformations and coupling reactions. In prokaryotes, both common sugar precursors and their enzymatically modified derivatives often become substituents of biologically active natural products through the action of glycosyltransferases. Recently, researchers have begun to harness the power of these biological catalysts to alter the sugar structures and glycosylation patterns of natural products both in vivo and in vitro. Biochemical and structural studies of sugar biosynthetic enzymes and glycosyltransferases, coupled with advances in bioengineering methodology, have ushered in a new era of drug development.

Facile synthesis of sulfonium ion derivatives of 1,5-anhydro-5-thio-l-fucitol as potential α-l-fucosidase inhibitors

Five sulfonium ion derivatives with 1,5-anhydro-5-thio-L-fucitol as a core structure were efficiently synthesized as potential alpha-L-fucosidase inhibitors. The key unit, the tri-O-benzyl derivative of L-fucitol, was readily synthesized from methyl alpha-D-mannopyranoside. Alkylation with methyl iodide or 5-methoxycarbonyl-1-pentyl iodide in acetonitrile containing AgBF4 afforded the corresponding alkylated sulfonium tetrafluoroborates. Alternatively, ring opening of three 1,3-cyclic sulfates in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) containing K2CO3 afforded the corresponding zwitterionic sulfonium sulfates.

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.

Purification, Kinetic Characterization, and Mapping of the Minimal Catalytic Domain and the Key Polar Groups of Helicobacter pylori α-(1,3/1,4)-Fucosyltransferases

The minimal catalytic domain of alpha-(1,3/1,4)-fucosyltransferases (FucTs) from Helicobacter pylori strains NCTC11639 and UA948 was mapped by N- and C-terminal truncations. Only the C terminus could be truncated without significant loss of activity. 11639FucT and UA948FucT contain 10 and 8 heptad repeats, respectively, which connect the catalytic domain with the C-terminal putative amphipathic alpha-helices. Deletion of all heptad repeats almost completely abolished enzyme activity. Nevertheless, with only one heptad repeat 11639FucT is fully active, whereas UA948FucT is partially active. Removal of the two putative amphipathic alpha-helices dramatically increased protein expression and solubility, enabling purification with yields of milligrams/liter. Steady-state kinetic analysis of the purified FucTs showed that 11639FucTs possessed slightly tighter binding affinity for both Type II acceptor and GDP-fucose donor than UA948FucT, and its kcat of 2.3 s(-1) was double that of UA948FucT, which had a kcat value of 1.1 s(-1) for both Type II and Type I acceptors. UA948FucT strongly favors Type II over the Type I acceptor with a 20-fold difference in acceptor Km. Sixteen modified Type I and Type II series acceptors were employed to map the molecular determinants of acceptors required for recognition by H. pylori alpha-(1,3/1,4)-FucTs. Deoxygenation at 6-C of the galactose in Type II acceptor caused a 5000-fold decrease in alpha1,3 activity, whereas in Type I acceptor this completely abolished alpha1,4 activity, indicating that this hydroxyl group is a key polar group.

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.

Reaction mechanism and substrate specificity for nucleotide sugar of mammalian alpha1,6-fucosyltransferase--a large-scale preparation and characterization of recombinant human FUT8

FUT8, mammalian alpha1,6-fucosyltransferase, catalyzes the transfer of a fucose residue from the donor substrate, guanosine 5'-diphosphate (GDP)-beta-L-fucose, to the reducing terminal GlcNAc of the core structure of asparagine-linked oligosaccharide via an alpha1,6-linkage. FUT8 is a typical type II membrane protein, which is localized in the Golgi apparatus. We have previously shown that two neighboring arginine residues that are conserved among alpha1,2-, alpha1,6-, and protein O-fucosyltransferases play an important role in donor substrate binding. However, details of the catalytic and reaction mechanisms and the ternary structure of FUT8 are not understood except for the substrate specificity of the acceptor. To develop a better understanding of FUT8, we established a large-scale production system for recombinant human FUT8, in which the enzyme is produced in soluble form by baculovirus-infected insect cells. Kinetic analyses and inhibition studies using derivatives of GDP-beta-L-fucose revealed that FUT8 catalyzes the reaction which depends on a rapid equilibrium random mechanism and strongly recognizes the base portion and diphosphoryl group of GDP-beta-L-fucose. These results may also be applicable to other fucosyltransferases and glycosyltransferases.

Iminosugars as glycosyltransferase inhibitors: synthesis of polyhydroxypyrrolidines and their evaluation on chitin synthase activity

Chitin synthase is an enzyme involved in the biosynthesis of chitin, a major structural component of the cell wall of many fungi. Since chitin is absent in vertebrates, chitin synthase has been envisaged as a valuable target in the search for new antifungal agents. In this report, a series of C-2 substituted polyhydroxypyrrolidines were designed and synthesized with the aim of mimicking the glycosylation involved at the transition state of the enzymatic reaction governed by chitin synthase. Some of these models displayed chitin synthase inhibition in the millimolar range. However, no significant antifungal activity was noted on a panel of fungal strains.

A single aromatic amino acid at the carboxyl terminus of Helicobacter pylori {alpha}1,3/4 fucosyltransferase determines substrate specificity

Fucosyltransferases (FucT) from different Helicobacter pylori strains display distinct Type I (Galbeta1,3GlcNAc) or Type II (Galbeta1,4GlcNAc) substrate specificity. FucT from strain UA948 can transfer fucose to the OH-3 of Type II acceptors as well as to the OH-4 of Type I acceptors on the GlcNAc moiety, so it has both alpha1,3 and alpha1,4 activities. In contrast, FucT from strain NCTC11639 has exclusive alpha1,3 activity. Our domain swapping study (Ma, B., Wang, G., Palcic, M. M., Hazes, B., and Taylor, D. E. (2003) J. Biol. Chem. 278, 21893-21900) demonstrated that exchange of the hypervariable loops, (347)DNPFIFC(353) in 11639FucT and (345)CNDAHYSALH(354) in UA948FucT, were sufficient to either confer or abolish alpha1,4 activity. Here we performed alanine scanning site-directed mutagenesis to identify which amino acids within (345)CNDAHYSALH(354) of UA948FucT confer Type I substrate specificity. The Tyr(350) --> Ala mutation dramatically reduced alpha1,4 activity without lowering alpha1,3 activity. None of the other alanine substitutions selectively eliminated alpha1,4 activity. To elucidate how Tyr(350) determines alpha1,4 specificity, mutants Tyr(350) --> Phe, Tyr(350) --> Trp, and Tyr(350) --> Gly were constructed in UA948FucT. These mutations did not decrease alpha1,3 activity but reduced the alpha1,4 activity to 66.9, 55.6, and 3.1% [corrected] of wild type level, respectively. Apparently the aromatic nature, but not the hydroxyl group of Tyr(350), is essential for alpha1,4 activity. Our data demonstrate that a single amino acid (Tyr(350)) in the C-terminal hypervariable region of UA948FucT determines Type I acceptor specificity. Notably, a single aromatic residue (Trp) has also been implicated in controlling Type I acceptor preference for human FucT III, but it is located in an N-terminal hypervariable stem domain.

Stachybotrydial, a potent inhibitor of fucosyltransferase and sialyltransferase

Elevated expression of fucosylated glycoconjugates and fucosyltransferases (Fuc-Ts) is found in various tumor cells and has been correlated with aspects of tumor progression such as cell adhesion and metastasis. Thus, fucosyltransferase inhibitors are potentially useful as anti-tumor agents. In the present study, three known spirocyclic drimanes (1, 2, and 3) were isolated from the culture broth of the fungus Stachybotrys cylindrospora. Compound 1 (stachybotrydial) exhibits potent inhibitory activity against alpha1,3-fucosyltransferase (Fuc-TV) during screening, while compounds 2 and 3 show no such inhibitory activity. Kinetic analysis indicates that compound 1 is an uncompetitive inhibitor with respect to GDP-fucose and a noncompetitive inhibitor with respect to N-acetyllactosamine with Ki values of 10.7 and 9.7 microM, respectively. In addition, all three compounds also possess inhibitory activity against sialyltransferase (ST) but not against beta1,4-galactosyltransferase. These observations provide novel chemical structure information that will help in the design of novel Fuc-T and ST inhibitors.

Identification of selective inhibitors for the glycosyltransferase MurG via high-throughput screening

Nucleotide-glycosyltransferases (NDP-Gtfs) play key roles in a wide range of biological processes. It is difficult to probe the roles of individual glycosyltransferases or their products because, with few exceptions, selective glycosyltransferase inhibitors do not exist. Here, we investigate a high-throughput approach to identify glycosyltransferase inhibitors based on a fluorescent donor displacement assay. We have applied the screen to E. coli MurG, an enzyme that is both a potential antibiotic target and a paradigm for a large family of glycosyltransferases. We show that the compounds identified in the donor-displacement screen of MurG are selective for MurG over other enzymes that use similar or identical substrates, including structurally related enzymes. The donor displacement assay described here should be adaptable to many other NDP-Gtfs and represents a new strategy to identify selective NDP-Gtf inhibitors.

The merits of bipartite transition-state mimics for inhibition of uracil DNA glycosylase

The glycosidic bond hydrolysis reaction of the enzyme uracil DNA glycosylase (UDG) occurs by a two-step mechanism involving complete bond breakage to the uracil anion leaving group in the first step, formation of a discrete glycosyl cation-uracil anion intermediate, followed by water attack in a second transition-state leading to the enzyme-bound products of uracil and abasic DNA. We have synthesized and determined the binding affinities of unimolecular mimics of the substrate and first transition-state (TS1) in which the uracil base is covalently attached to the sugar, and in addition, bimolecular mimics of the second addition transition state (TS2) in which the base and sugar are detached. We find that the bipartite mimics of TS2 are superior to the TS1 mimics. These results indicate that bipartite TS2 inhibitors could be useful for inhibition of glycosylases that proceed by stepwise reaction mechanisms.

C-terminal amino acids of Helicobacter pylori alpha1,3/4 fucosyltransferases determine type I and type II transfer

The alpha1,3/4 fucosyltransferase (FucT) enzyme from Helicobacter pylori catalyzes fucose transfer from donor GDP-beta-l-fucose to the GlcNAc group of two series of acceptor substrates in H. pylori lipopolysaccharide: betaGal1,3betaGlcNAc (Type I) or betaGal1,4betaGlcNAc (Type II). Fucose is added either in alpha1,3 linkage of Type II acceptor to produce Lewis X or in alpha1,4 linkage of Type I acceptor to produce Lewis A, respectively. H. pylori FucTs from different strains have distinct Type I or Type II substrate specificities. FucT in H. pylori strain NCTC11639 has an exclusive alpha1,3 activity because it recognizes only Type II substrates, whereas FucT in H. pylori strain UA948 can utilize both Type II and Type I acceptors; thus it has both alpha1,3 and alpha1,4 activity, respectively. To identify elements conferring substrate specificity, 12 chimeric FucTs were constructed by domain swapping between 11639FucT and UA948FucT and characterized for their ability to transfer fucose to Type I and Type II acceptors. Our results indicate that the C-terminal region of H. pylori FucTs controls Type I and Type II acceptor specificity. In particular, the highly divergent C-terminal portion, seven amino acids DNPFIFC at positions 347-353 in 11639FucT, and the corresponding 10 amino acids CNDAHYSALH at positions 345-354 in UA948FucT, controls the Type I and Type II acceptor recognition. This is the opposite of mammalian FucTs where acceptor preference is determined primarily by the N-terminal residues in the hypervariable stem domain.

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.

Chemical and biological strategies for engineering cell surface glycosylation

Oligosaccharides play a crucial role in many of the recognition, signaling, and adhesion events that take place at the surface of cells. Abnormalities in the synthesis or presentation of these carbohydrates can lead to misfolded and inactive proteins, as well as to several debilitating disease states. However, their diverse structures, which are the key to their function, have hampered studies by biologists and chemists alike. This review presents an overview of techniques for examining and manipulating cell surface oligosaccharides through genetic, enzymatic, and chemical strategies.

Carbohydrate mimetics-based glycosyltransferase inhibitors

The search for carbohydrate mimetics-based glycosyltransferase inhibitors is a dynamic field that emerged 10 years ago. This review presents a description of the different types of glycosyltransferase inhibitors containing a carbohydrate mimetic (primarily an iminosugar, a carbasugar or a C-glycoside) and data on their biological activity whenever such data are available. The purpose of this account is to foster a synergy between the two expanding research areas of glycomimetics and glycosyltransferases.

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.

First asymmetric hetero Diels-Alder reaction of 1-sulfinyl dienes with nitroso derivatives. A new entry to the synthesis of optically pure 1,4-imino-L-ribitol derivatives

Hetero Diels-Alder (HDA) cycloaddition of chiral 1-p-tolylsulfinyl-1,3-pentadiene with benzyl nitrosoformate, under mild conditions, yields 2H-1,2-oxazine 3 with complete regioselectivity and pi-facial diastereoselectivity. Sequential osmylation and protection of the resulting glycol gives the oxazine 5 which is directly transformed into enantiomerically pure 1,4,5-trideoxy-1,4-imino-L-ribitol 8 by reduction under Pd/C.

Glycosyltransferase structure and mechanism

The high-resolution X-ray crystal structures of a new form of bacteriophage T4 beta-glucosyltransferase, Escherichia coli MurG, Bacillus subtilis SpsA, bovine beta-1,4-galactosyltransferase 1 and rabbit N-acetylglucosaminyltransferase I have now been solved. These glycosyltransferase structures have provided the first detailed view of the structural basis of catalysis, as well as new insight into glycosyltransferase classification.

Synthesis and enzymatic evaluation of five-membered iminocyclitols and a pseudodisaccharide

Described here are the synthesis of five-membered iminocyclitols with galacto-configuration and a pseudodisaccharide, and their inhibitory activities against beta-galactosyltransferase, beta-galactosidase and alpha-mannosidase.

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.