Discrimination between Human Colorectal Neoplasms with a Dual-Recognitive Two-Photon Probe

Colorectal cancer is a major cause of cancer-related deaths worldwide. Histologic diagnosis using biopsy samples of colorectal neoplasms is the most important step in determining the treatment methods, but these methods have limitations in accuracy and effectiveness. Herein, we report a dual-recognition two-photon probe and its application in the discrimination between human colorectal neoplasms. The probe is composed of two monosaccharides, d-glucosamine and β-d-galactopyranoside, in a fluorophore for the monitoring of both glucose uptake and β-gal hydrolysis. In vitro/cell imaging studies revealed the excellent selectivity and sensitivity of the probe for glucose transporter-mediated glucose uptake and β-gal activity. Cancer-specific uptake was monitored by increased fluorescence intensity, and additional screening of cancer cells was achieved by changes in emission ratio owing to the higher activity of β-gal. Using human colon tissues and two-photon microscopy, we found that the plot of intensity versus ratio can accurately discriminate between colorectal neoplasms in the order of cancer progression (normal, adenoma, and carcinoma).

[Synthesis and acceptor properties of 11-[(9'-anthracenyl)methoxy]undecyl phosphate and P1-{11-[(9'-anthracenyl)methoxy]undecyl}-P2-(alpha-D-galactopyranosyl) diphosphate in the enzymic reactions catalyzed by galactosylphosphotransferase and mannosyltransferase from Salmonella newport]

Fluorescent 11-[(9'-anthracenyl)methoxy]undecyl phosphate and P1-{11-[(9'-anthracenyl)methoxy]undecyl}-P2-(alpha-D-galactopyranosyl) diphosphate were chemically synthesized for the first time. The ability of the first compound to serve as substrate-acceptor ofgalactosyl phosphate residue and the second compound of mannosyl residue in enzymic reactions catalyzed by galactosylphosphotransferase and mannosyltransferase from Salmonella newport membrane preparation was demonstrated.

Highly efficient synthesis and antitumor activity of monosaccharide saponins mimicking components of Chinese folk medicine Cordyceps sinensis

Ergosterol 3-O-β-D-glucopyranoside (1a) and ergosterol 3-O-β-D-galactopyranoside (1b) were highly efficiently synthesized and evaluated for their inhibitory activities against two tumor cell lines. The structures of these compounds were extensively confirmed by (1)H, (13)C NMR, IR, and HRMS. Compounds 1a and 1b exhibited interesting cytotoxic profiles. The antitumor activity of compound 1a was higher than that of 1b.

Glycosylated nordihydroguaiaretic acids as anti-cancer agents

Three perglycosylated nordihydroguaiaretic acids (NDGA) were synthesized through the Huiseng 1,3-dipolar cycloaddition reaction. These sugar-NDGA conjugates containing triazole-linkages possessed good solubility in water. NDGA-(triazol-galactose)(4) (12b) and NDGA-(triazol-glucose)(4) (12c) were found to act as inhibitors against human hepatocellular carcinoma Hep3B cells in culture.

Enzymatic synthesis and characterization of hydroquinone galactoside using Kluyveromyces lactis lactase

Hydroquinone galactoside (HQ-Gal) as a potential skin whitening agent was synthesized by the reaction of lactase (beta-galactosidase) from Kluyveromyces lactis, Aspergillus oryzae, Bacillus circulans, and Thermus sp. with lactose as a donor and HQ as an acceptor. Among these lactases, the acceptor reaction involving HQ and lactose with K. lactis lactase showed a higher conversion ratio to HQ-Gal (60.27%). HQ-Gal was purified using butanol partitioning and silica gel column chromatography. The structure of the purified HQ-Gal was determined by nuclear magnetic resonance, and the ionic product was observed at m/z 295 (C12H16O7Na)+ using matrix assisted laser desorption ionization time-of-flight mass spectrometry. HQ-Gal was identified as 4-hydroxyphenyl-beta-d-galactopyranoside. The optimum conditions for HQ-Gal synthesis by K. lactis determined using response surface methodology were 50 mM HQ, 60 mM lactose, and 20 U mL(-1) lactase. These conditions produced a yield of 2.01 g L(-1) HQ-Gal. The half maximal inhibitory concentration (IC50) of diphenylpicrylhydrazyl scavenging activity was 3.31 mM, indicating a similar antioxidant activity compared to beta-arbutin (IC50=3.95 mM). The Ki value of HQ-Gal (0.75 mM) against tyrosinase was smaller than that of beta-arbutin (Ki=1.97 mM), indicating its superiority as an inhibitor. HQ-Gal inhibited (23%) melanin synthesis without being significantly toxic to the cells, while beta-arbutin exhibited only 8% reduction of melanin synthesis in B16 melanoma cells compared with the control. These results indicate that HQ-Gal may be a suitable functional component in the cosmetics industry.

Synthesis and characterization of a new fluorogenic substrate for alpha-galactosidase

Alpha-galactosidase A hydrolyzes the terminal alpha-galactosyl moieties from glycolipids and glycoproteins in lysosomes. Mutations in alpha-galactosidase cause lysosomal accumulation of the glycosphingolipid, globotriaosylceramide, which leads to Fabry disease. Small-molecule chaperones that bind to mutant enzyme proteins and correct their misfolding and mistrafficking have emerged as a potential therapy for Fabry disease. We have synthesized a red fluorogenic substrate, resorufinyl alpha-D-galactopyranoside, for a new alpha-galactosidase enzyme assay. This assay can be measured continuously at lower pH values, without the addition of a stop solution, due to the relatively low pK(a) of resorufin (approximately 6). In addition, the assay emits red fluorescence, which can significantly reduce interferences due to compound fluorescence and dust/lint as compared to blue fluorescence. Therefore, this new red fluorogenic substrate and the resulting enzyme assay can be used in high-throughput screening to identify small-molecule chaperones for Fabry disease.

Development of pyrrolo[2,1-c][1,4]benzodiazepine beta-galactoside prodrugs for selective therapy of cancer by ADEPT and PMT

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a class of well-studied DNA-interactive agents with a potential for use in the treatment of cancer. The clinical utility of these molecules is limited because of the lack of selectivity for tumor tissues, high reactivity of the pharmacophoric imine functionality, low water solubility, and stability. To address the shortcomings, especially the lack of selectivity, associated with the molecules, two new beta-galactoside prodrugs of PBDs have been synthesized and evaluated for their potential use in selective therapy of solid tumors by ADEPT and PMT protocols. The preliminary studies reveal the prodrugs to be much less toxic compared to the parent moieties. These prodrugs are activated by E. coli beta-galactosidase (EC 3.2.1.23) to form the active cytotoxic moiety signifying their utility in ADEPT of cancer. One of the significant outcomes of the present study is the toxification of the prodrug 1 a by the endogenous beta-galactosidase of human liver cancer cells (Hep G2) to form the cytotoxic moiety, enabling selective therapy of hepatocellular carcinoma. Another important property of these molecules is their enhanced water solubility and stability, which are essential for a molecule to be an effective drug.

Radiosynthesis and evaluation of 5-[125I]iodoindol-3-yl-beta-D-galactopyranoside as a beta-galactosidase imaging radioligand

The synthesis and investigation of 5-[125I]iodoindol-3-yl-beta-d-galactopyranoside ([125I]IBDG) as a radioligand for single-photon emission computed tomography (SPECT) imaging of b-galactosidase expression are described. No-carrier-added [125I]IBDG was synthesized by a radioiododestannylation approach in > 75% overall radiochemical yield and > 99% radiochemical purity. [125I]IBDG was evaluated as a substrate using beta-galactosidase-expressing (D54L) and nonexpressing (D54) human glioma cell lines. A 24-hour incubation of this substrate with cultured cells revealed a 6.5-fold greater intracellular trapping of radioactivity in D54L cells compared with D54 cells. Systemic delivery of [125I]IBDG in nude mice bearing D54L tumors failed to show significant trapping of radioactivity within these tumors by SPECT imaging. In contrast, intratumoral injection of the substrate resulted in efficient trapping of radioactivity in D54L tumors but not D54 tumors, resulting in clear SPECT visualization of the former tumor. Based on dynamic SPECT imaging and blood metabolite analysis, we conclude that although [125I]IBDG is an efficient in vivo substrate for beta-galactosidase, its rapid renal clearance hampers its intratumoral availability on systemic administration.

Beta-galactoside prodrugs of doxorubicin for application in antibody directed enzyme prodrug therapy/prodrug monotherapy

Anthracycline antibiotics, particularly doxorubicin and daunorubicin, have been used exten sively in the treatment of human malignancies. However cardiotoxicity and multidrug resistance are significant problems that limit the clinical efficacy of such agents. Rational design to avoid these side effects includes strategies such as drug targeting and prodrug synthesis. Described here are the synthesis and preliminary biological evaluation of the enzymatically activated two new prodrugs (6 & 11) of doxorubicin. These prodrugs were designed as potential candidates for selective chemotherapy in ADEPT or PMT strategies. They are constituted of a galactose moiety, a spacer and the cytotoxic drug and they differ by the type of spacer. The prodrugs were stable in a buffer, and the in vitro studies showed good detoxification and hydrolysis kinetics. As prodrug 11 was readily hydrolyzed, this could be a valuable candidate for further development.

Zeolite-catalyzed Helferich-type glycosylation of long-chain alcohols. Synthesis of acetylated alkyl 1,2-trans glycopyranosides and alkyl 1,2-cis C2-hydroxy-glycopyranosides

Zeolite-catalyzed glycosylation of long-chain alcohols, using the inexpensive and readily available peracetylated beta-D-gluco- and galactopyranoses as glycosyl donors under solvent free conditions, has been explored for the first time. Among the various forms (H-, Na-, Fe- and Zn) of beta zeolite examined as catalysts in the reaction of 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose with cetyl alcohol, Fe-beta zeolite gave the maximum yield of 63% of cetyl 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranoside and cetyl 3,4,6-tri-O-acetyl-alpha-D-galactopyranoside. Fe-beta Zeolite-catalyzed glycosylation was found to be general affording the title compounds in each case in a moderate yield, but with a good stereoselectivity. The yield of synthetically valuable acetylated long-chain alkyl 1,2-cis C2-hydroxy-glycopyranosides obtained in the present single-step procedure is considerably higher than that of the previously reported multi-step method employing the Stork silicon tether approach.

Carbonic Anhydrase Inhibitors: Inhibition of Isozymes I, II, and IX with Triazole-LinkedO-Glycosides of Benzene Sulfonamides

We report the synthesis of a series of benzene sulfonamides containing triazole-O-glycoside tails for evaluation as carbonic anhydrase (CA) inhibitors. These glycoconjugates were synthesized by the 1,3-dipolar cycloaddition reaction of 4-azidobenzenesulfonamide with O-propynyl glycosides. Compounds were assessed for their ability to inhibit the enzymatic activity of the physiologically dominant isozymes hCA I and II and the tumor-associated isozyme hCA IX (h = human). Against hCA I these compounds were either micromolar or low-nanomolar inhibitors, while against hCA II and IX inhibition in the range of 6.8-53 and 9.7-107 nM, respectively, was observed. The most potent inhibitor against hCA IX was the galactose derivative 8 (Ki = 9.7 nM); this is so far the most potent glycoconjugate inhibitor reported for the tumor-associated hCA IX. These carbohydrate-tethered sulfonamides may prove interesting lead candidates to target tumor-associated CA isozymes, wherein the CA domain is located extracellularly.

Synthesis and biological evaluation of the suberoylanilide hydroxamic acid (SAHA) β-glucuronide and β-galactoside for application in selective prodrug chemotherapy

The beta-O-glucuronide and beta-O-galactoside of SAHA have been prepared and evaluated as prodrugs for selective cancer chemotherapy (ADEPT, PMT). These new compounds are stable under physiological conditions and do not exhibit any antiproliferative activity compared to the parent drug after a 48-h treatment of H661 cells. The glucuronide derivative did not lead to the release of the drug in the presence of either Escherichia coli or bovine liver beta-glucuronidase. On the other hand, under enzymatic cleavage of galactoside prodrug by the corresponding enzyme, a rapid release of SAHA was observed demonstrating that the beta-O-galactoside of SAHA is a promising candidate for in vivo investigations.

2,3-Anhydrosugars in Glycoside Bond Synthesis. Application to α-d-Galactofuranosides

We report here the use of 2,3-anhydro-D-gulofuranosyl thioglycosides and glycosyl sulfoxides in the synthesis of alpha-D-galactofuranosidic bonds, which are present in a range of bacterial and fungal glycoconjugates. This two-step method involves a stereoselective glycosylation in which a 2,3-anhydro-alpha-D-gulofuranoside is obtained either as the sole or as the major product, followed by a regioselective opening of the epoxide ring using lithium benzylate in the presence of (-)-sparteine. In exploring the scope of the method, donors protected at O5 and O6 with an isopropylidene acetal, benzyl ethers, or benzoate esters were studied. Overall, the glycosyl sulfoxides provided the products in slightly higher yields and selectivity, with the best results being obtained with benzylated and benzoylated substrates. In the epoxide ring-opening reactions, the acetal- and ether-protected donors afforded poor to modest regioselectivity, whereas the benzoylated products gave good yields of the desired alpha-D-galactofuranosides. The benzoyl-protected species are, therefore, the donors of choice for these reactions. The utility of the approach was demonstrated through the synthesis of three alpha-D-galactofuranosyl-containing oligosaccharides.

Facile synthesis of benzyl β-d-galactofuranoside. A convenient intermediate for the synthesis of d-galactofuranose-containing molecules

Benzyl beta-D-galactofuranoside was efficiently obtained from 1,2,3,5,6-penta-O-benzoyl-alpha,beta-D-galactofuranose, via benzyl 2,3,5,6-tetra-O-benzoyl-beta-D-galactofuranoside. Conditions for the O-debenzylation were investigated in order to evaluate the synthetic application of the benzyl group as an anomeric protector of a galactofuranose moiety in synthetic strategies involving galactofuranose.

Synthesis of a library of fucopyranosyl-galactopyranosides consisting of a complete set of anomeric configurations and linkage positions

A library composed of a complete set of fucopyranosyl-galactopyranosides was synthesized. A perbenzylated phenylthio fucopyranoside and a series of tri-O-benzyl-galactopyranosyl fluorides having single hydroxyl groups at the 2-, 3-, 4-, and 6-positions were used as the glycosyl donor and glycosyl acceptors, respectively. The chosen set of functionalities at the anomeric centers enabled rapid access to the oligosaccharides based on chemoselective activation. The first coupling reaction was achieved by the action of dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST). The resulting disaccharide fluoride was readily activated by hafnocene bistrifluoromethanesulfonate [Cp2Hf(OTf)2] and glycosidated with n-octanol.

Photodynamic Efficiency of Diethylene Glycol-Linked Glycoconjugated Porphyrins in Human Retinoblastoma Cells

Photodynamic therapy (PDT) is emerging as a new strategy for the conservative treatment of hereditary retinoblastoma. The glycoconjugated porphyrins TPP(p-Deg-O-alpha-GalOH)(3), TPP(p-Deg-O-beta-GalOH)(3), TPP(p-Deg-O-alpha-ManOH)(3), and their S-analogues were synthesized to obtain efficient photosensitizers with some retinoblastoma cell affinity. In these systems, a sugar motif and porphyrin core were linked by a diethylene glycol spacer (Deg). Cellular uptake, localization, and photoactivity have been examined in human retinoblastoma cells (Y79). After preincubation with corresponding glycosylated albumin, the uptake of TPP(p-Deg-O-beta-GalOH)(3) and TPP(p-Deg-O-alpha-ManOH)(3) was 40-45% inhibited, indicating a possible cell-sugar-receptor saturation. High photoactivity was observed for the two alpha-galacto/manno porphyrins 8 and 10 (LD(50) = 0.05 and 0.35 muM, respectively) at 514 nm and low fluence (1 J/cm(2)). Analysis by MALDI-TOF mass spectrometry only indicated a small metabolic cleavage of the O-glycoconjugates and a good stability of the S-glycoside porphyrins. On the basis of these in vitro data, TPP(p-Deg-O-alpha-GalOH)(3) and TPP(p-Deg-O-alpha-ManOH)(3) were selected for in vivo studies.

Selective Synthesis of α-C-(Alkynyl)-galactosides by an Efficient Tandem Reaction

Several alpha-C-(alkynyl)-galactosides were synthesized using a tandem reaction involving the addition of a metal alkynylide to a chiral acyclic epoxyaldehyde, followed by an in situ closure of the generated alkoxide on the epoxide function.

Synthesis of a novel galactosylated lipid and its application to the hepatocyte-selective targeting of liposomal doxorubicin

This paper described the synthesis of a novel galactosylated lipid with mono-galactoside moiety, (5-Cholesten-3beta-yl) 4-oxo-4-[2-(lactobionyl amido) ethylamido] butanoate (CHS-ED-LA), and the targetability of doxorubicin (DOX), a model drug, in liposomes containing 10% mol/mol CHS-ED-LA (galactosylated liposomes, GalL) to the liver was studied. The weighted-average overall drug targeting efficiency (Te(*)) was used to evaluate the liver targetability of GalL DOX. The results showed that GalL DOX gave a relatively high (Te(*))(liver) value of 64.6%, while DOX in conventional liposome (CL DOX) only gave a (Te(*))(liver) value of 21.8%. In the liver, the GalL DOX was mainly taken up by parenchymal cells (88% of the total hepatic uptake). Moreover, preinjection of asialofetuin significantly inhibited the liver uptake of GalL DOX (from 70 to 12% of the total injected dose). It was suggested that liposomes containing such novel galactosylated lipid, CHS-ED-LA, had a great potential as drug delivery carriers for hepatocyte-selective targeting.

Stereoselective single-step synthesis and X-ray crystallographic investigation of acetylated aryl 1,2-trans glycopyranosides and aryl 1,2-cis C2-hydroxy-glycopyranosides

Reported is an attractive and environmentally friendly method for the synthesis of the title compounds in moderate yield using inexpensive 1,2,3,4,6-penta-O-acetyl-beta-D-gluco- and galactopyranoses as sugar donors, five different phenols as acceptors and H-beta zeolite as the catalyst. The yield (23-28%) of aryl 3,4,6-tri-O-acetyl-alpha-D-glycopyranosides obtained in this single-step procedure is considerably higher than that obtained using previously reported methods. Treatment of an orthoacetate, 3,4,6-tri-O-acetyl-[1,2-O-(1-p-fluorophenoxyethylidene)]-alpha-D-glucopyranose, with p-fluorophenol under the same solvent-free reaction conditions also led to the formation of the title compounds in similar yield and composition. X-ray crystallographic analysis of phenyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside and p-fluorophenyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside showed that the molecular packing is stabilized by C-H...O, C-H...pi and C-H...F interactions, in addition to regular hydrogen bonding patterns.

3-(1,2,3-Triazol-1-yl)-1-thio-galactosides as small, efficient, and hydrolytically stable inhibitors of galectin-3

Copper(I)-catalyzed addition of alkynes to methyl 3-azido-3-deoxy-1-thio-beta-D-galactopyranoside afforded stable and structurally simple 3-deoxy-3-(1H-1,2,3-triazol-1-yl)-1-thio-galactosides carrying a panel of substituents at the triazole C4 in high yields. The 3-(1H-[1,2,3]-triazol-1-yl)-1-thio-galactoside collection synthesized contained inhibitors of the tumor- and inflammation-related galectin-3 with Kd values as low as 107 microM, which is as potent as the natural disaccharide inhibitors lactose and N-acetyllactosamine.

Synthesis and Evaluation of a Novel Gene Reporter Molecule: Detection of b-galactosidase Activity Using 19F NMR of a Fluorinated Vitamin B6 Conjugate+

Gene therapy has emerged as a promising strategy for treatment of various diseases. However, widespread implementation is hampered by difficulties in assessing the success of transfection, in particular, the spatial extent of expression in the target tissue and the longevity of expression. Thus, the development of non-invasive reporter techniques based on appropriate molecules and imaging modalities may help to assay gene expression. We now report the design, synthesis and evaluation of a novel in vivo gene transfection reporter molecule 3-O-(beta-D-galactopyranosyl)-6-fluoropyridoxol (GFPOL) using fluorinated vitamin B(6) as the (19)F NMR sensitive aglycone. GFPOL exhibits the following strengths as an in vivo (19)F NMR gene expression reporter: (a) large chemical shift response to enzyme cleavage (Deltadelta=8.00 ppm); (b) minimal toxicity for substrate or aglycone; (c) good water solubility; (d) good blood stability; (e) pH responsiveness of aglycone.

De Novo Enantioselective Syntheses of Galacto-Sugars and Deoxy Sugars via the Iterative Dihydroxylation of Dienoate

An efficient route to various sugar lactones has been developed. Key to the overall transformation is the sequential osmium-catalyzed dihydroxylation of 2,4-dienoates. The simplest (one-step/racemic) example of this reaction occurs when the dihydroxylation is performed with aqueous NMO in MeOH. When the first dihydroxylation is performed using the AD-mix procedure, an enantioselective variant results. When a matched AD-mix procedure is used for the second dihydroxylation, an exceedingly diastereo- and enantioselective synthesis of galacto-1,4-lactone results. [Reaction: see text]

Novel NMR Platform for Detecting Gene Transfection: Synthesis and Evaluation of Fluorinated Phenyl β-d-Galactosides with Potential Application for Assessing LacZ Gene Expression

Gene therapy holds great promise for the treatment of diverse diseases, but widespread implementation is hindered by difficulties in assessing the success of transfection. The development of noninvasive reporter techniques based on appropriate molecules and imaging modalities may help to assay gene expression. Fluorophenyl-beta-d-galactopyranosides provide a novel class of NMR active molecules, which are highly responsive to the action of beta-galactosidase (beta-gal), the product of the lacZ gene. The reporter molecules are stable in solution and with respect to wild-type cells, but the enzyme causes liberation of the aglycon, a fluorophenol, accompanied by distinct color formation and a (19)F NMR chemical shift of 5-10 ppm, depending on pH. Synthetic strategy, experimental methods, and molecular and (19)F NMR characteristics are reported for a series of molecules in solution, blood, and tumor cells. This class of molecules presents a new strategy for assaying gene expression with a highly versatile molecular structural platform.

Novel polysulfated galactose-derivatized dendrimers as binding antagonists of human immunodeficiency virus type 1 infection

Evidence indicates that galactosyl ceramide (GalCer) and its 3'-sulfated derivative, sulfatide (SGalCer), may act as alternate coreceptors for human immunodeficiency virus type 1 (HIV-1) in CD4(-) cells. Glycosphingolipids (GSLs) may also be necessary for fusion of HIV-1 and host cell membranes. Using an enzyme-linked immunosorbent assay to determine which GSL was the best ligand for both recombinant and virus-associated gp120, we found that SGalCer was the best ligand for each rgp120 and HIV-1 isolate tested. Therefore, novel multivalent glycodendrimers, which mimic the carbohydrate clustering reportedly found in lipid rafts, were synthesized based on the carbohydrate moiety of SGalCer. Here we describe the synthesis of a polysulfated galactose functionalized, fifth generation DAB dendrimer (PS Gal 64mer), containing on average two sulfate groups per galactose residue. Its ability to inhibit HIV-1 infection of cultured indicator cells was compared to that of dextran sulfate (DxS), a known, potent, binding inhibitor of HIV-1. The results indicate that the PS Gal 64mer inhibited infection by the HIV-1 isolates tested as well as DxS.

A New Reaction for the Direct Conversion of 4-Azido-4-deoxy-d-galactoside into a 4-Deoxy-d-erythro-hexos-3-ulose

[reaction: see text] A new one-step reaction has been developed for converting 4-azido-4-deoxy-d-galactoside into 4-deoxy-d-erythro-hexos-3-ulose by phosphoramidites and tetrazole. It is proposed that the new reaction proceeds via an intramolecular Staudinger reaction of the phosphite intermediate and a tetrazole-catalyzed elimination reaction of the resultant phosphorimidate. Tetrazole appears to be playing a unique role by acting as a bifunctional catalyst to facilitate the elimination reaction.

3,5-Substituted phenyl galactosides as leads in designing effective cholera toxin antagonists

With the aim of developing high-affinity mono and multivalent antagonists of cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) we are using the galactose portion of the natural receptor ganglioside GM1 as an anchoring fragment in structure-based inhibitor design efforts. In order to establish a better structure-activity relationship for guiding these studies, we designed and prepared a small focused library of twenty 3,5-substituted phenylgalactosides based on two previous leads. The compounds were tested for their ability to block CTB(5) binding to immobilized ganglioside receptor and compared to the two previous leads. The crystal structures of the most promising compounds bound to either CTB(5) or LTB(5) were then determined in order to understand the basis for affinity differences. The most potent new compound yielded a six-fold improvement over our benchmark lead m-nitrophenyl-alpha-d-galactopyranoside (MNPG), and a two-fold improvement in IC(50) over a newer MNPG derivative. These results support the notion that the m-nitrophenyl moiety of MNPG and its derivatives is an important element to retain in future optimization efforts. Additionally, a consensus binding-pocket for the alkylmorpholine or piperazine moiety present in all of the designed antagonists was established as an important area of the GM1 binding site to target in future work.

Selective synthesis and reactions of 6-substituted-2-beta-galactosyl-1,2,4-triazines of potential anticancer activity

Selective synthesis and reactions of different 6-substituted-2-beta-D-galactosyl-3-thioxo-2,3-dihydro-1,2,4-triazin-5(4H)-ones using the developed amino or aryl protecting group strategy were investigated. Primary human anticancer screening of twelve selected compounds (in vitro) resulted in an active compound against both MCF7 (Breast) and SF-268(CNS) cell lines.

Synthesis and conformational analysis of arabinofuranosides, galactofuranosides and fructofuranosides

Many microorganisms produce biologically important polysaccharides containing galactofuranosyl, arabinofuranosyl and/or fructofuranosyl residues. Recent interest in identifying antibiotics that act by inhibiting the biosynthesis of these glycans has resulted in the development of new and efficient methods for the assembly of oligosaccharides containing furanose residues. In general, it is now possible to synthesize any furanose-containing oligosaccharide with reasonable efficiency. In conjunction with these synthetic investigations, an increasing number of studies have probed the conformation of furanose rings, and a solid appreciation of the conformational preferences of key furanoside ring systems is now available.

Sialoside specificity of the siglec family assessed using novel multivalent probes: identification of potent inhibitors of myelin-associated glycoprotein

Ten of the 11 known human siglecs or their murine orthologs have been evaluated for their specificity for over 25 synthetic sialosides representing most of the major sequences terminating carbohydrate groups of glycoproteins and glycolipids. Analysis has been performed using a novel multivalent platform comprising biotinylated sialosides bound to a streptavidin-alkaline phosphatase conjugate. Each siglec was found to have a unique specificity for binding 16 different sialoside-streptavidin-alkaline phosphatase probes. The relative affinities of monovalent sialosides were assessed for each siglec in competitive inhibition studies. The quantitative data obtained allows a detailed analysis of each siglec for the relative importance of sialic acid and the penultimate oligosaccharide sequence on binding affinity and specificity. Most remarkable was the finding that myelin-associated glycoprotein (Siglec-4) binds with 500-10,000-fold higher affinity to a series of mono- and di-sialylated derivatives of the O-linked T-antigen (Galbeta(1-3)-GalNAc(alpha)OThr) as compared with alpha-methyl-NeuAc.

Stereoselective synthesis of 2-deoxy-beta-galactosides via 2-deoxy-2-bromo- and 2-deoxy-2-iodo-galactopyranosyl donors

[reaction: see text] A series of 2-bromo- and 2-iodo-galactopyranosyl acetates and trichloroacetimidates were evaluated as glycosyl donors for the synthesis of 2-deoxygalactopyranosides. The best selectivity for the beta-glycosidic linkage was achieved by using 6-deoxy-3,4-carbonate-protected galactosyl donors.

Synthesis of novel cyclic oligosaccharides: beta-1,6-thio-linked cycloglucopyranosides

[structure: see text] A protocol for the synthesis of novel cyclic beta-1,6-S-linked glucopyranosides is developed. The key intermediate is a linear thiooligosaccharide bearing an iodo group at C-6 of the nonreducing sugar and a thioacetyl group at the anomeric center of the reducing end sugar. The crucial macrocyclization step was achieved through base-promoted intramolecular S(N)2 glycosylation in remarkably high yields (92-95%) and with well-controlled stereochemistry.

Synthesis of an ether-linked alkyl 5a-carba-beta-D-glucoside, a 5a-carba-beta-D-galactoside, a 2-acetamido-2-deoxy-5a-carba-beta-D-glucoside, and an alkyl 5a'-carba-beta-lactoside

For the purpose of providing biologically stable building blocks for the biocombinatorial synthesis using a living cell, some ether-linked alkyl 5a-carba-beta-D-glycoside primers were prepared. The key step of the synthesis was coupling of 1-bromo-n-alkanes with the 1-OH unprotected derivatives of 5a-carba-sugar analogues of D-glucose, D-galactose, and 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), in DMF in the presence of sodium hydride. Alternatively, alkyl carba-lactoside was synthesized by incorporation of a 5a-carba-beta-D-galactose residue into the 4-position of dodecyl beta-D-glucopyranoside. A strong and specific inhibition of beta-galactosidase (K(i) 0.67 microM, bovine liver) was found for dodecyl 5a-carba-beta-D-galactopyranoside.

A convenient synthesis of C-galactofuranosylic compounds (C-galactofuranosides)

Galactofuranose sugar units are essential for the production of the cell coat of many pathogenic microorganisms. This sugar is not found in mammals, and so compounds that may interfere with the biosynthetic processing of this sugar unit provide interesting targets for drug design. This paper describes the use of a cyanation reaction for the production of a one-carbon extension of a galactofuranosylic unit at C-1, giving 2,5-anhydro-3,4,6,7-tetra-O-benzoyl-D-glycero-L-manno-heptononitrile. A procedure for the efficient hydrolysis of the introduced nitrile group to produce the methyl ester is reported, along with procedures for the synthesis of both the corresponding alpha,beta-unsaturated, and 3-deoxy ester derivatives.

Linear synthesis of the tumor-associated carbohydrate antigens Globo-H, SSEA-3, and Gb3

The tumor-associated carbohydrate antigens Globo-H, SSEA-3, and Gb3 were synthesized in a linear fashion using glycosyl phosphate monosaccharide building blocks. All of the building blocks were prepared from readily available common precursors. The difficult alpha-(1-->4-cis)-galactosidic linkage was installed using a galactosyl phosphate donor with high selectivity. Introduction of the beta-galactosamine unit required the screening a variety of amine protecting groups to ensure good donor reactivity and protecting group compatibility. An N-trichloroacetyl-protected galactosamine donor performed best for the installation of the beta-glycosidic linkage. Conversion of the trichloroacetyl group to the N-acetyl group was achieved under mild conditions, fully compatible with the presence of multiple glycosidic bonds. This synthetic strategy is expected to be amenable to the synthesis of the globo-series of tumor antigens on solid-support.

Discovery of potent inhibitors of PapG adhesins from uropathogenic Escherichia coli through synthesis and evaluation of galabiose derivatives

The synthesis of two galabioside (Galalpha1-4Gal) collections based on diversification at the O-1 and O-3' atoms is reported. The galabiosides were evaluated as inhibitors of hemagglutination of human erythrocytes by two strains of Escherichia coli that expressed the class I and class II PapG adhesins, respectively. The class I adhesin was found to prefer aromatic substituents both at the O-1 and the O-3' position of the galabiose disaccharide. One galabioside, p-methoxyphenyl [3-O-(m-nitrobenzyl)-alpha-D-galactopyranosyl]-(1-4)-beta-D-galactopyranoside], had an IC(50) value of 4.1 microM, which is the best inhibition of the class I adhesin to date. In the case of the class II adhesin, one inhibitor, 2-[(S)-2-methoxycarbonyl-2-acetamido-ethylthio]ethyl (3-O-3-[2-(methoxycarbonylphenylthio)propyl]-alpha-D-galactopyranosyl)-(1-4)-alpha-D-galactopyranoside, was found to have an IC(50) value of 68 microM, which is the best artificial inhibition of the class II adhesin reported so far with an affinity for the adhesin comparable to that of the natural tetrasaccharide ligand globotetraose.

Linear total synthetic routes to beta-D-C-(1,6)-linked oligoglucoses and oligogalactoses up to pentaoses by iterative Wittig olefination assembly

Two complementary routes, A and B, have been followed for the stepwise iterative assembly of beta-D-(1,6)-glucopyranose and galactopyranose residues through methylene bridges. In route A the building block was constituted by 2,3,4-tri-O-benzyl-6-O-tert-butyldiphenylsilyl (O-TBDPS) beta-linked galactosylmethylenephosphorane, while in route B the building block was a beta-linked formyl C-glycopyranoside with a similar orthogonal protection of hydroxy groups. In route A each cycle consisted of the reaction of the phosphorane building block with a sugar residue bearing a formyl group at the C-5 carbon atom (coupling) and transformation of the O-TBDPS-protected primary alcohol into the formyl group (arming). Accordingly, route A is defined as the aldehyde route. On the other hand, each cycle in route B involved the coupling of the sugar aldehyde building block with a substrate bearing a phosphorus ylide at C-6 and introduction of the phosphonium group in the arming step as a precursor of the ylide functionality. Accordingly, route B is defined as the ylide route. The efficiency of route A proved to be seriously hampered by the 1,2-elimination of BnOH under the basic reaction conditions of the Wittig olefination, giving rise to the formation of substantial amounts of enopyranose. On the other hand, the ylide route B proved to be more efficient since very good yields (70-93%) of the isolated Wittig products were obtained throughout four consecutive cycles. Individual olefins and polyolefins obtained by routes A and B using gluco and galacto substrates were reduced and debenzylated in one pot by H(2)/Pd(OH)(2) to give the corresponding beta-D-C-(1,6)-linked oligosaccharides up to the pentaose stage. The latter compounds were fully characterized by high-field NMR spectroscopy (500 MHz).

1-O-Acetyl-beta-D-galactopyranose: a novel substrate for the transglycosylation reaction catalyzed by the beta-galactosidase from Penicillium sp

1-O-Acetyl-beta-D-galactopyranose (AcGal), a new substrate for beta-galactosidase, was synthesized in a stereoselective manner by the trichloroacetimidate procedure. Kinetic parameters (K(M) and k(cat)) for the hydrolysis of 1-O-acetyl-beta-D-galactopyranose catalyzed by the beta-D-galactosidase from Penicillium sp. were compared with similar characteristics for a number of natural and synthetic substrates. The value for k(cat) in the hydrolysis of AcGal was three orders of magnitude greater than for other known substrates. The beta-galactosidase hydrolyzes AcGal with retention of anomeric configuration. The transglycosylation activity of the beta-D-galactosidase in the reaction of AcGal and methyl beta-D-galactopyranoside (1) as substrates was investigated by 1H NMR spectroscopy and HPLC techniques. The transglycosylation product using AcGal as a substrate was beta-D-galactopyranosyl-(1-->6)-1-O-acetyl-beta-D-galactopyranose (with a yield of approximately 70%). In the case of 1 as a substrate, the main transglycosylation product was methyl beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranoside. Methyl beta-D-galactopyranosyl-(1-->3)-beta-D-galactopyranoside was found to be minor product in the latter reaction.

Dendritic galactosides based on a beta-cyclodextrin core for the construction of site-specific molecular delivery systems: synthesis and molecular recognition studies

In order to evaluate the ability of multivalent glycosides based on a beta-cyclodextrin core as site-specific molecular carriers, a study on both the inclusion complexation behaviour and lectin binding affinity of branched and hyperbranched beta-cyclodextrins is presented. A series of cluster galactosides constructed on beta-cyclodextrin scaffolds containing seven 1-thio-beta-lactose or beta-lactosylamine bound to the macrocyclic core through different spacer arms were synthesised. In addition, the first synthesis of three first-order dendrimers based on a beta-cyclodextrin core containing fourteen 1-thio-beta-D-galactose, 1-thio-beta-lactose and 1-thio-beta-melibiose residues was performed. Calorimetric titrations performed at 25 degrees C in buffered aqueous solution (pH 7.4) gave the affinity constants and the thermodynamic parameters for the complex formation of these beta-cyclodextrin derivatives with guests sodium 8-anilino-1-naphthalenesulfonate (ANS) and 2-naphthalenesulfonate, and lectin from peanut (Arachis hypogaea) (PNA). The persubstitution of the primary face of the beta-cyclodextrin with saccharides led to a slight increase of the binding constant values for the inclusion complexation with ANS relative to the native beta-cyclodextrin. However, the increase of the steric congestion due to the presence of the saccharide residues on the narrow rim of the beta-cyclodextrin may cause a decrease of the binding ability as shown for sodium 2-naphthalenesulfonate. The spacer arms are not passive elements and influence the host binding ability according to their chemical nature. PNA forms soluble cross-linked complexes with cluster galactosides and lactosides scaffolded on beta-cyclodextrin but not with cluster galactopyranosylamines or melibiose. Both, perbranched and hyperbranched beta-cyclodextrins, form stronger complexes with PNA than the monomeric analogues. However, the use of hyperbranched CDs does not contribute to the improvement of the complex stability relative to heptakis-glycocyclodextrin derivatives. Finally, a titration experiment with PNA and a complex formed by a heptakis lactose beta-cyclodextrin derivative with sodium 2-naphthalenesulfonate showed the formation of a soluble cross-linked complex with stronger affinity constant and higher stoichiometry than those observed for the complex formation of PNA with the same heptakis-lactose beta-cyclodextrin derivative, suggesting the formation of a three component complex.

Synthesis and evaluation of novel fluorogenic substrates for the detection of bacterial beta-galactosidase

AIMS

A widely used coumarin derivative is 7-hydroxy-4-methylcoumarin-beta-D-galactoside (4-methylumbelliferone-beta-D-galactoside; 4-MU-GAL). This galactoside is utilized as a substrate for the detection of the beta-galactosidase activity of coliform bacteria in water analysis. The intense fluorescence of coumarin-based molecules has enabled them to be incorporated into enzyme-based tests for the quantitative assay of indicator bacteria. The aim of this present study was to evaluate the potential of other coumarin derivatives, by synthesis of a selection of core coumarin molecules.

METHODS AND RESULTS

Several coumarin derivatives were found to be more promising than 4-MU, with ethyl-7-hydroxycoumarin-3-carboxylate (EHC) giving a combination of greater fluorescence over a broad pH range and reduced growth inhibition with 12 representative coliform strains. On conversion to a beta-galactoside derivative, EHC-GAL generated a more rapid fluorescence than any other tested substrate.

CONCLUSIONS

When tested in a broth assay format, based on most probable number (MPN), low numbers of coliforms were detected with EHC-GAL around 1 h earlier than with 4-MU-GAL.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study suggests that EHC-GAL should be evaluated as a substrate for the detection of coliforms in water analysis, due to a combination of the following favourable features: (i) reduced toxicity; (ii) increased fluorescence; (iii) pH stability of fluorescence; and (iv) rapid detection.

Highly diastereoselective 1,4-addition of an organocuprate to methyl alpha-D-gluco-, alpha-D-manno-, or alpha-D-galactopyranosides tethering an alpha,beta-unsaturated ester. Novel asymmetric access to beta-C-substituted butanoic acids

The 1,4-addition of magnesium divinylcuprate prepared from vinylmagnesium bromide and cuprous bromide to some 4-O-crotonyl derivatives of methyl alpha-D-glucopyranoside proceeds with a high level of diastereochemical induction, providing the adduct in good-to-excellent yields. Other organocuprates also serve as effective carbon nucleophiles for the 1,4-addition. Removal of the carbohydrate moiety from each adduct afforded a variety of beta-C-substituted butanoic esters in remarkable enantiomeric excess. The 1,4-addition of the same cuprate to some methyl alpha-D-manno- or alpha-D-galactopyranosidic substrates in which a crotonyl group was incorporated, each at 3-OH, was also investigated. The reverse pi-facial attack of the cuprate was observed when some D-manno-type substrates were subjected to 1,4-addition conditions similar to those used for the D-gluco-type substrates. Furthermore, some D-galacto-type substrates provided 1,4-adducts with higher diastereoselectivities.

Synthesis and structure determination of some oxadiazole-2-thione and triazole-3-thione galactosides

The syntheses of 5-pyridyl-3(beta-D-galactopyranosyl)-1,3,4-oxadiazole-2-thiones 3a-3c and 5-pyridyl-2(beta-D-galactopyranosyl)-4-benzyl-1,2, 4-triazole-3-thiones 6a-6c are reported. The existence of N-galactosides--not S-galactosides--was proven by IR and 15N NMR spectroscopy. The structures of the final products and the intermediates were elucidated by IR, 1H, 13C and 15N NMR spectroscopy and mass spectrometry.

Preparation of 1,2-O-isopropylidene derivatives of alpha-D-galactoseptanose, beta-L-altroseptanose, and 3-O-methyl-alpha-D-guloseptanose

Displacement of the tosyloxy group in 5-O-benzyl-1,2-O-isopropylidene-4-O-(p-toluenesulfonyl)-alpha-D-glucoseptanose has yielded derivatives of 1,2-O-isopropylidene-alpha-D-galactoseptanose. Acid catalysed acetonation then gave 1,2:3,4-di-O-isopropylidene-alpha-D-galactoseptanose or 1,2;4,5-di-O-isopropylidene-alpha-D-galactoseptanose using lower acid concentrations. Reduction of the ketone derived from 1,2:3,4-O-isopropylidene-alpha-D-septanose gave 1,2;3,4-di-O-isopropylidene-beta-L-altroseptanose. Reaction of 3,4-anhydro-5-O-benzyl-1,2-O-isopropylidene-alpha-D-galactoseptanose with sodium methoxide gave 5-O-benzyl-1,2-O-isopropylidene-4-O-methyl-alpha-D-glucoseptanose and 5-O-benzyl-1,2-O-isopropylidene-3-O-methyl-alpha-D-guloseptanose. Solution-state conformations of these compounds have been deduced from their 1H NMR spectra.

A stereoselective approach for the synthesis of alpha-sialosides

A highly efficient synthesis of the human melanoma associated antigen GD(3) derivative has been described. A key feature of the synthetic approach was the use of sialyl donors that were protected with a C-5 trifluoroacetamide moiety. These sialyl donors gave high yields and excellent alpha-anomeric selectivities in direct glycosylations with a wide variety of glycosyl acceptors ranging from C-8 hydroxyls of sialic acids and C-3 hydroxyls of galactosides to reactive primary alcohols.

Synthesis of beta-D-galactofuranosyl nucleoside analogues. A new type of beta-D-galactofuranosidase inhibitor

The development of beta-D-galactofuranosidase inhibitors provides a good chemotherapeutic target for treatment of major human diseases, because beta-D-galactofuranose is a constituent of important pathogen microorganisms but is absent in mammals. With this purpose we have prepared beta-D-galactofuranosyl nucleoside analogues, derived by the addition of nucleophiles to perbenzoylated beta-D-galactofuranosyl isothiocyanate, a compound previously prepared in this laboratory. N-beta-D-Galactofuranosyl-O-ethylthiourethane, N-beta-D-galactofuranosyl-4-oxoimidazolidine-2-thione, N-beta-D-galactofuranosyl-4-imidazoline-2-thione, and N-beta-D-galactofuranosyl-4-methoxyimidazolidine-2-thione, were prepared. The biological assays showed that imidazoline and imidazolidine-2-thione derivatives act as a new type of exo beta-D-galactofuranosidase inhibitor.

A Convergent Strategy for the Synthesis of β-Carba-galacto-disaccharides

[reaction in text] A convergent strategy for the synthesis of beta-carba-galacto-disaccharides is illustrated by the preparation of 1 and 4, from a central "glycone" component 22, and the corresponding "aglycone" segments, monosaccharide alcohols, 23a or 23b. The key step is the formation of the carbasugar ring via an oxocarbenium ion-enol ether cyclization.

Evaluation of p-naphtholbenzein-beta-D-galactoside as a substrate for bacterial beta-galactosidase

We describe the synthesis of a new substrate for the detection of beta-galactosidase and evaluate its performance in comparison with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) and cyclohexenoesculetinbeta-D-galactoside (CHE-Gal). Of 206 Enterobacteriaceae strains able to hydrolyze X-Gal, 194 (94.2%) hydrolyzed CHE-Gal and 192 (93.2%) hydrolyzed p-naphtholbenzein-beta-D-galactoside (PNB-Gal). We conclude that PNB-Gal is an effective substrate for the detection of beta-galactosidase.

Synthesis of galactosyl and lactosyl derivatives as potential anti-metastasis compounds

Based on the known anti-metastasis activities of lactosides and galactosides, a galactosyl and a lactosyl trimannoside were prepared via the conventional Koenigs-Knorr and trichloroacetimidate methods, respectively. Through typical deblocking procedures, a tetrasaccharide alpha-D-Galp-(1 --> 2)-alpha-D-Manp-(1 --> 2)-alpha-D-Manp-(1 --> 6)-alpha-D-ManpOCH3 and a pentasaccharide beta-D-Galp-(1 --> 4)-beta-D-Glcp-(1 --> 2)-alpha-D-Manp-(1 --> 2)-alpha-D-Manp-(1 --> 6)-alpha-D-ManpOCH3 were obtained.

Synthesis of single- and double-chain fluorocarbon and hydrocarbon galactosyl amphiphiles and their anti-HIV-1 activity

Galactosylceramide (GalCer) is an alternative receptor allowing HIV-1 entry into CD4(-)/GalCer(+) cells. This glycosphingolipid recognizes the V3 loop of HIV gp120, which plays a key role in the fusion of the HIV envelope and cellular membrane. To inhibit HIV uptake and infection, we designed and synthesized analogs of GalCer. These amphiphiles and bolaamphiphiles consist of single and double hydrocarbon and/or fluorocarbon chain beta-linked to galactose and galactosamine. They derive from serine (GalSer), cysteine (GalCys), and ethanolamine (GalAE). The anti-HIV activity and cytotoxicity of these galactolipids were evaluated in vitro on CEM-SS (a CD4(+) cell line), HT-29, a CD4(-) cell line expressing high levels of GalCer receptor, and/or HT29 genetically modified to express CD4. GalSer and GalAE derivatives, tested in aqueous medium or as part of liposome preparation, showed moderate anti-HIV-1 activities (IC50 in the 20-220 microM range), whereas none of the GalCys derivatives was found to be active. Moreover, only some of these anti-HIV active analogs inhibited the binding of [3H]suramin (a polysulfonyl compound which displays a high affinity for the V3 loop) to SPC3, a synthetic peptide which contains the conserved GPGRAF region of the V3 loop. Our results most likely indicate that the neutralization of the virion through masking of this conserved V3 loop region is not the only mechanism involved in the HIV-1 antiviral activity of our GalCer analogs.

Syntheses and properties of photoactivatable sugar derivatives designed to probe the sugar-binding site of melibiose permease

Three new photoreactive sugar analogues bearing an azido, a diazonium salt or a diazirine group as the photophore as well as a tritium atom were developed. Two of these new photoactivatable compounds gave excellent preliminary results, with a high affinity for the melibiose permease of Escherichia coli.

Alizarin-beta-D-galactoside: a new substrate for the detection of bacterial beta-galactosidase

We describe the synthesis of a new substrate for the detection of bacterial beta-galactosidase. This substrate, alizarin-beta-D-galactoside, is readily hydrolysed to release alizarin which complexes with various metal ions to form brightly coloured chelates. A total of 367 strains of Gram-negative bacteria were examined for their ability to hydrolyse three chromogenic substrates: alizarin-beta-D-galactoside (Aliz-gal), cyclohexenoesculetin-beta-D-galactoside (CHE-gal) and 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-gal). A total of 182 strains (49.6%) were found to hydrolyse at least one of the three substrates. All of these 182 strains (100%) hydrolysed Aliz-gal whereas only 170 (93.4%) and 173 (95.1%) hydrolysed CHE-gal and X-gal, respectively. We conclude that alizarin-beta-D-galactoside is a highly sensitive substrate for the demonstration of beta-galactosidase.