Synthesis of alpha-Gal C-disaccharides.

The synthesis of C-disaccharides of α-d-galactopyranosyl-(1 → 3)-d-galactopyranose (α-Gal), potential tools for studying the biology of α-Gal glycans, is described. The synthetic strategy, centers on the reaction of two easily available precursors 1,2-O-isopropylidene-d-glyceraldehyde and an α-C-glactosyl-E-crotylboronate, which affords a mixture of two diastereomeric anti-crotylation products. The stereoselectivity of this reaction was controlled with (R)- and (S)-TRIP catalysts, and the appropriate diastereomer was transformed to C-linked disaccharides of α-Gal, in which the aglycone segment comprised O-, C- and S-glycoside entities that can enable glycoconjugate synthesis.

Targeting Carbohydrate Mimetics of Tetrahydrofuran-Containing Acetogenins to Prostate Cancer.

The high potency of the tetrahydrofuran-containing acetogenins (THF-ACGs) against a broad range of human cancer cell lines has stimulated interest in structurally simpler mimetics. In this context, we have previously reported THF-ACG mimetics in which the THF and butenolide moieties of a mono-THF-ACG were replaced with carbohydrate and thiophene residues, respectively. In the present study, towards the targeting of these carbohydrate analogues to prostate cancer (PCa), we synthesized prodrugs in which a parent thiophene or butenolide congener was conjugated through a self-immolative linker to 2-[3-(1,3-dicarboxypropyl)ureido] pentanedioic acid (DUPA), a highly specific ligand for prostate-specific membrane antigen (PSMA), which is overexpressed on prostate tumors.

Synthesis of carbohydrate analogues of the THF-acetogenin 4-deoxyannomontacin and their cytotoxicity against human prostate cancer cell lines.

The THF containing acetogenin 4-deoxyannonmontacin (4-DAN) has attracted interest for its potent cytotoxicity against a broad range of human tumor cell lines, and relatively simple structure. Herein is described the synthesis and cytotoxicity of C-10 epimers of 4-DAN and analogues thereof comprising carbohydrate and thiophene substitutes for the THF and butenolide moieties respectively. The key synthetic ploy was the union of THF and butenolide segments or their substitutes, via an alkene cross metathesis.

Oxocarbenium ion cyclizations for the synthesis of disaccharide mimetics of 2-amino-2-deoxy-pyranosides: Application to the carbasugar of β-galactosamine-(1,4)-3-O-methyl-D-chiro-inositol.

The synthesis of the carbasugar of β-galactosamine-(1,4)-3-O-methyl-D-chiro-inositol (INS-2), a potential tool for studying glucose metabolism, is described. The synthetic strategy, entails an oxocarbenium ion cyclization on a chiro-inositol derived, thioacetal-enol ether to give a carbocyclic enol ether, which is elaborated to the 2-amino-2-deoxy carbasugar framework via a 2-oximo derivative.

-Glycosylcrotylboronates for the Synthesis of Glycomimetics.

The stereoselective synthesis of - and - isomers of a - crotylpinacolboronate Ni-promoted reactions on an allylic acetate and a diene precursor, respectively, is described. The - and - isomers reacted with 1,2--isopropylidene glyceraldehyde in the presence or absence of ()- and ()- TRIP catalysts, to give predominantly 3,4- and 3,4- crotylation products, respectively, with moderate to high facial selectivity. These products were transformed to biologically relevant --disaccharides.

Glycopolymer Microarrays with Sub-Femtomolar Avidity for Glycan Binding Proteins Prepared by Grafted-To/Grafted-From Photopolymerizations.

We report a novel glycan array architecture that binds the mannose-specific glycan binding protein, concanavalin A (ConA), with sub-femtomolar avidity. A new radical photopolymerization developed specifically for this application combines the grafted-from thiol-(meth)acrylate polymerization with thiol-ene chemistry to graft glycans to the growing polymer brushes. The propagation of the brushes was studied by carrying out this grafted-to/grafted-from radical photopolymerization (GTGFRP) at >400 different conditions using hypersurface photolithography, a printing strategy that substantially accelerates reaction discovery and optimization on surfaces.

Multivalent binding of concanavalin A on variable-density mannoside microarrays.

Interactions between cell surface glycans and glycan binding proteins (GBPs) have a central role in the immune response, pathogen-host recognition, cell-cell communication, and a myriad other biological processes. Because of the weak association between GBPs and glycans in solution, multivalent and cooperative interactions in the dense glycocalyx have an outsized role in directing binding affinity and selectivity. However, a major challenge in glycobiology is that few experimental approaches exist for examining and understanding quantitatively how glycan density affects avidity with GBPs, and there is a need for new tools that can fabricate glycan arrays with the ability to vary their density controllably and systematically in each feature.

Maskless Photochemical Printing of Multiplexed Glycan Microarrays for High-Throughput Binding Studies.

Spatially encoded glycan microarrays promise to rapidly accelerate our understanding of glycan binding in myriad biological processes, which could lead to new therapeutics and previously unknown drug targets. Here, we bring together a digital micromirror device, microfluidic introduction of inks, and advanced surface photochemistry to produce multiplexed glycan microarrays with reduced feature diameters, an increased number of features per array, and precise control of glycan density at each feature. The versatility of this platform was validated by printing two distinct glycan microarrays where, in the first, different glycans were immobilized to create a multiplexed array and, in another, the density of a single glycan was varied systematically to explore the effect of surface presentation on lectin-glycan binding.

Abrogation of Endogenous Glycolipid Antigen Presentation on Myelin-Laden Macrophages by D-Sphingosine Ameliorates the Pathogenesis of Experimental Autoimmune Encephalomyelitis.

Although myelin is composed of mostly lipids, the pathological role of myelin lipids in demyelinating diseases remains elusive. The principal lipid of the myelin sheath is β-galactosylceramide (β-Galcer). Its α-anomer (α-Galcer) has been demonstrated to be antigenically presented by macrophages via CD1d, a MHC class I-like molecule.

Synthesis of C-Glycoinositols from C-Glycosylcrotylstannanes.

A strategy for the synthesis of C-pseudodisaccharides that centers on the reaction of a C-linked crotyltin and a substituted pent-4-enal and a ring-closing metathesis-alkene dihydroxylation sequence on the derived crotylation products is illustrated in the preparation of analogues of the insulin modulatory inositol galactosamine-β-(1 → 4)-3-O-methyl-d- chiro-inositol (β-INS-2). The modularity of this approach and versatility of the pivotal crotylation products make this a potentially general methodology for diverse libraries of C-glycoinositols.

Synthesis and biological activities of C-glycosides of KRN 7000 with novel ceramide residues.

The identification of immunoactive agents for clinical and mechanistic applications is a very active area of research. In this vein, analogues of the potent immunostimulant KRN 7000 with diverse cytokine profiles have attracted considerable attention. These compounds have been shown to activate iNKT cells via presentation by CD1d.

The Crotylation Way to Glycosphingolipids: Synthesis of Analogues of KRN7000.

A synthesis of glycosphingolipids that centers on the reaction of O- and C-glycosyl crotylstannanes and relatively simple lipid aldehydes is described. The modularity of this strategy and versatility of the crotylation products make this an attractive approach to diverse, highly substituted libraries. The methodology is applied to analogues of the potent imunostimulatory glycolipid KRN7000, including O-, methylene-, and fluoromethine-linked isosteres with diastereomeric ceramide segments and 2-amido substitutes.

A ring closing metathesis strategy for carbapyranosides of xylose and arabinose.

The synthesis of β-carba-xylo and arabino pyranosides of cholestanol is described. The synthetic strategy, which is analogous to the Postema approach to C-glycosides, centers on the ring closing metathesis of an enol ether-alkene precursor to give a cyclic enol ether that is elaborated to a carba-pyranoside via hydroboration-oxidation on the olefin. The method, which is attractive for its modularity and stereoselectivity, may find wider applications to carba-hexopyranosides and other complex cycloalkyl ether frameworks.

A ring closing metathesis strategy for carbapyranosides of xylose and arabinose.

The synthesis of β-carba-xylo and arabino pyranosides of cholestanol is described. The synthetic strategy, which is analogous to the Postema approach to C-glycosides, centers on the ring closing metathesis of an enol ether-alkene precursor to give a cyclic enol ether that is elaborated to a carba-pyranoside via hydroboration-oxidation on the olefin. The method, which is attractive for its modularity and stereoselectivity, may find wider applications to carba-hexopyranosides and other complex cycloalkyl ether frameworks.

An organocatalytic strategy for the stereoselective synthesis of C-galactosides with fluorine at the pseudoanomeric carbon.

The α-fluorination of α- and β-C-ethanals of galactose using Jørgensen catalysts and NFSI was investigated. The crude reaction products were transformed to their primary alcohol or methylenated derivatives, which are versatile precursors to biologically interesting fluorinated glycomimetics. The α-C-glycoside substrate gave moderate to high yields of fluorinated α-C-glycosides with minor amounts of β-C-glycoside analogues.

C-glycosphingolipid precursors via iodocyclization of homoallyic trichloroacetimidates.

The iodocyclization of homoallylic trichloroacetimidates derived from α-C-allyl galactoside were investigated. In line with the stereochemical trend observed for less substituted non-glycosylated frameworks, E and Z substrates delivered stereoselectively the 1,3-anti and 1,3-syn amino alcohol motifs, respectively. These products are advanced precursors to C-glycosides of the potent immunostimulatory glycolipid KRN7000.

Intramolecular nitrogen delivery for the synthesis of C-glycosphingolipids. Application to the C-glycoside of the immunostimulant KRN7000.

The key reaction in this approach to C-glycosphingolipids is the stereoselective iodocyclization of a sugar-linked homoallylic carbonimidothioate. E and Z reaction substrates were assembled in a convergent fashion via an alkene metathesis strategy and exhibited the same alkene facial selectivity in the iodocyclization irrespective of alkene geometry, although the E alkene was found to be less reactive.

Synthesis of the C-glycoside of α-(D)-mannose-(1 → 6)-(D)-myo-inositol.

The dimannosylatedinositol pseudotrisaccharide phospholipid of the lipoarabinomannan (LAM) component of the mycobacterial cell wall has attracted interest as a therapeutic target because of its uniqueness to mycobacteria, its assembly at an early stage in LAM biosynthesis and the immunological activity of oligosaccharides containing this subunit. Accordingly, analogues of this pseudotrisaccharide, α-d-mannose-(1 → 2)-α-d-mannose-(1 → 6)-d-myo-inositol are of interest as mechanistic probes and drug leads. C-glycosides are of special interest because of their hydrolytic stability and conformational differences compared to O-glycosides.

Synthesis and anti-tumor activity of carbohydrate analogues of the tetrahydrofuran containing acetogenins.

The tetrahydrofuran (THF) containing annonaceous acetogenins (AAs) are attractive candidates for drug development because of their potent cytotoxicity against a wide range of tumors and their relatively simple and robust structures. Replacement of the THF segment with a sugar residue may deliver analogues with improved tumor selectivity and pharmacokinetics and are therefore attractive for drug development. As a first test to the feasibility of such structures, a set of such monosaccharide analogues was synthesized and assayed against four human tumor cell lines, cervical (HeLa), breast (MDA-MB231), T-cell leukemia (Jurkat) and prostate (PC-3).

Synthesis of an A'B' Precursor to Angelmicin B: Product Diversification in the Suárez Lactol Fragmentation.

We describe a synthetic strategy for the angelimicin family of anthraquinoid natural products that involves converting a central highly oxygenated decalin intermediate to the AB and A'B' subunits. Herein, we report the synthesis of the bicyclic A'B' subunit that complements our earlier route to the tricyclic AB framework. The differentiating tact in the two syntheses focused on controlling the Suárez radical fragmentation of lactol precursors by modulating the substrate's structural rigidity.

Synthesis, gp120 binding and anti-HIV activity of fatty acid esters of 1,1-linked disaccharides.

Inspired by the anti-human immunodeficiency virus (HIV) activity of analogues of β-galactosylceramide (GalCer), a set of mono- and di-saccharide fatty acid esters were designed as GalCer mimetics and their binding to the V3 loop peptide of HIV-1 and anti-HIV activity evaluated. 1,1-linked Gal-Man and Glu-Man disaccharides with an ester on the Man subunit bound the V3 loop peptide and inhibited HIV infectivity in single round infection assays with the TZM-bl cell line. IC(50)'s were in the 50 μM range with no toxicity to the cells at concentrations up to 200 μM.

Synthesis of C-glycoside analogues of beta-galactosamine-(1-->4)-3-O-methyl-D-chiro-inositol and assay as activator of protein phosphatases PDHP and PP2Calpha.

The glycan beta-galactosamine-(1-4)-3-O-methyl-D-chiro-inositol, called INS-2, was previously isolated from liver as a putative second messenger-modulator for insulin. Synthetic INS-2 injected intravenously in rats is both insulin-mimetic and insulin-sensitizing. This bioactivity is attributed to allosteric activation of pyruvate dehydrogenase phosphatase (PDHP) and protein phosphatase 2Calpha (PP2Calpha).

Synthesis of the Mixed Acetal Segment of S-Glyceroplasmalopsychosine.

In this report the concept of converting carbohydrate to non-carbohydrate asymmetric molecules has been successfully exploited. The mixed acetal segment of glyceroplasmalopsychosine, a novel glycolipid has been synthesized in a stereo-specific manner using two simple sugar units. The glycosidation reaction between these two monosaccharides ensured the correct acetal stereocenter of the target molecule.

Olefin metathesis-iodoetherification-dehydroiodination strategy for spiroketal subunits of polyether antibiotics.

The convergent synthesis of two pentacyclic analogues of the polyether monensin A is described. Although different with respect to the configuration of the alcohol at the 3 position of the six-membered ring of the spiroketal subunit, the configuration at the acetal center in both structures is unchanged and is consistent with the anomeric effect. The key synthetic steps are the coupling of two complex segments via an olefin metathesis, and the subsequent conversion of a dihydroxyalkene to the spiroketal through an iodoetherification-dehydroiodination sequence.