A new, stereocontrolled approach to iminosugar C-glycosides from L-sorbose

The efficient synthesis of the iminoalditols derivatives 1 and 2 (nojirimycin alpha-C-glycosides) has been achieved in 10 steps from commercially available 2,3;4,6-di-O-isopropylidene-alpha-L-sorbofuranose in an overall yield of 23-27%.

Total synthesis of everninomicin 13,384-1--Part 4: explorations of methodology; stereocontrolled synthesis of 1,1'-disaccharides, 1,2-seleno migrations in carbohydrates, and solution- and solid-phase synthesis of 2-deoxy glycosides and orthoesters

Methods for the stereocontrolled construction of 1,1'-disaccharides, 2-deoxy glycosides, and orthoesters are reported. Specifically, a tin-acetal moiety was utilized to fix the anomeric stereochemistry of a carbohydrate acceptor leading to an efficient and stereoselective synthesis of 1,1'-disaccharides, while a newly discovered 1,2-phenylseleno migration reaction in carbohydrates opened entries to 2-deoxy glycosides and orthoesters. Thus, reaction of 2-hydroxy phenylselenoglycosides with DAST led to 2-phenylselenoglycosyl fluorides which reacted with carbohydrate acceptors to afford, stereoselectively, 2-phenylselenoglycosides. The latter compounds could be reductively deselenated to 2-deoxy glycosides or oxidatively converted to orthoesters via the corresponding ketene acetals.

Syntheses and biological evaluation of new glyco-modified angucyclin-antibiotics

The synthesis of novel aquayamycin-derived angucycline antibiotics 13a-d has been achieved. Glycosylation of aquayamycin (6) using 2-selenoglycosyl acetate 7 as glycosyl donor proceeded in excellent yield but attempts to reductively remove the selenyl group led to rearrangement or further aromatization of the aglycon. As a consequence of these results, it became possible to prepare urdamycinone B (10) starting from aquayamycin (6). In addition, silyl protected D-olivals 12a,b were attached to the C-glycoside domain of aquayamycin (6) under protic conditions. As expected, the hydroxy and phenol groups of the benz[a]anthracene framework of 6 did not react under the glycosylation conditions employed. Stepwise removal of the silyl protecting group starting with tetrabutyl ammonium fluoride followed by use of the HF/pyridine complex suppressed a possible rearrangement of the aglycon and successfully terminated the sequence. The new angucycline-antibiotics 13a and 13b are some of the most potent xanthine oxidase inhibitors known and show cytotoxic activity with ED50-values in the range of 12.6-2.9x 10(-6) M.

Aluminum- and boron-mediated c-glycoside synthesis from 1,2-anhydroglycosides

[reaction: see text]This letter describes a single flask strategy to the synthesis of alpha-C-glycosides from glycals. This protocol couples a glycal epoxidation reaction with a C-2 alkoxy-directed carbon-carbon bond-forming reaction.

A convenient preparation of glycosyl chlorides from aryl/alkyl thioglycosides

[reaction: see text]Because of the vast structural diversity encountered in the field of glycobiology, versatile methods for orthogonal oligosaccharide assembly are always of interest. Reported herein is the preparation of glycosyl chloride donors obtained by reaction of the corresponding thioglycoside precursors with chlorosulfonium chloride reagent 4. The crude chlorides thus obtained can be used directly in subsequent glycosylation reactions, and examples of the generality of this approach are provided.

Targeted glycosyl donor delivery for site-selective glycosylation

[reaction: see text]n-Pentenyl ortho esters (NPOEs) and n-pentenyl glycosides (NPGs) are interconvertible glycosyl donors which are activated by reaction with halonium ions. In a series of cyclic syn-1,3-diols, NPOEs have been found to specifically glycosylate the equatorial-OH while the NPG glycosylates predominantly, but not exclusively, the axial-OH. When the cyclic diol acceptor is presented with equivalent amounts of an NPOE and an NPG in a three-component-reaction, a single, double-glycosylation product is obtained, which conforms to the foregoing preferences, presenting evidence for site-selective glycosylation.

Identification of Asp-130 as the catalytic nucleophile in the main alpha-galactosidase from Phanerochaete chrysosporium, a family 27 glycosyl hydrolase

Characterization of the complete gene sequence encoding the alpha-galactosidase from Phanerochaete chrysosporium confirms that this enzyme is a member of glycosyl hydrolase family 27 [Henrissat, B., and Bairoch, A. (1996) Biochem. J. 316, 695-696]. This family, together with the family 36 alpha-galactosidases, forms glycosyl hydrolase clan GH-D, a superfamily of alpha-galactosidases, alpha-N-acetylgalactosaminidases, and isomaltodextranases which are likely to share a common catalytic mechanism and structural topology. Identification of the active site catalytic nucleophile was achieved by labeling with the mechanism-based inactivator 2',4', 6'-trinitrophenyl 2-deoxy-2,2-difluoro-alpha-D-lyxo-hexopyranoside; this inactivator was synthesized by anomeric deprotection of the known 1,3,4,6-tetra-O-acetyl-2-deoxy-2, 2-difluoro-D-lyxo-hexopyranoside [McCarter, J. D., Adam, M. J., Braun, C., Namchuk, M., Tull, D., and Withers, S. G. (1993) Carbohydr. Res. 249, 77-90], picrylation with picryl fluoride and 2, 6-di-tert-butylpyridine, and O-deacetylation with methanolic HCl. Enzyme inactivation is a result of the formation of a stable 2-deoxy-2,2-difluoro-beta-D-lyxo-hexopyranosyl-enzyme intermediate. Following peptic digestion, comparative liquid chromatographic/mass spectrometric analysis of inactivated and control enzyme samples served to identify the covalently modified peptide. After purification of the labeled peptide, benzylamine was shown to successfully replace the 2-deoxy-2,2-difluoro-D-lyxo-hexopyranosyl peptidyl ester by aminolysis. The labeled amino acid was identified as Asp-130 of the mature protein by further tandem mass spectrometric analysis of the native and derivatized peptides in combination with Edman degradation analysis. Asp-130 is found within the sequence YLKYDNC, which is highly conserved in all known family 27 glycosyl hydrolases.

Syntheses and stereochemical revision of pseudopterosin G-J aglycon and helioporin E

Revised structures are proposed for pseudopterosin G-J aglycon and helioporin E.

Synthesis of the C-glycosidic analogue of adenophostin A and its uracil congener as potential IP(3) receptor ligands. Stereoselective construction of the C-glycosidic structure by a temporary silicon-tethered radical coupling reaction

Synthesis of the C-glycosidic analogue 9 of adenophostin A, a very potent IP(3) receptor agonist, and its uracil congener 10 was achieved via a temporary silicon-tethered radical coupling reaction as the key step. Phenyl 3,4, 6-tri-O-(p-methoxybenzyl)-1-seleno-beta-D-glucopyranoside (27) and 3-deoxy-3-methylene-1, 2-O-isopropylidene-alpha-D-erythro-pentofuranose (30) were connected by a dimethylsilyl tether to give the radical coupling reaction substrate 24, which was successively treated with Bu(3)SnH/AIBN in benzene and TBAF in THF to give the coupling product 25 with the desired (3alpha,1'alpha)-configuration as the major product. From 25, the targets 9 and 10 were synthesized via introduction of adenine or uracil base by Vorbrüggen's method and phosphorylation of the hydroxyls by the phosphoramidite method.

Glycals in the stereoselective synthesis of triterpene 2-deoxy-alpha-L-glycosides under conditions of acidic catalysis

3beta-Hydroxy triterpenes of the oleanane, ursane, and lupane types were successfully glycosylated with acetylated L-glucal and L-rhamnal under conditions of acidic catalysis (anhydrous cation-exchange resin and LiBr). The 2-deoxy- and 2, 6-dideoxy-alpha-L-arabino-hexopyranosides (1-5) were stereoselectively prepared in 83-90% yields, following deacetylation under mild conditions, which led to the target triterpene 2-deoxy-alpha-L-glycosides (6-10).

Quercetin and its glycosides in the flowers of Asclepias syriaca L

The following flavonoid compounds have been isolated and identified from the flowers of Asclepiac syriaca L.: quercetin and its glycosides: 7-O-galactoside, 7-O-glucoside, 3-O-beta-D-xylopyranoside(1-->2) beta-D-galactoside and 3-O-beta-D-glucopyranoside(1-->2) beta-D-galactoside. Their structures were established by acid and enzymatic hydrolysis or H2O2 oxidation as well as spectral analysis (UV, 1H and 13C NMR).

Synthesis of glycosyl(thio)ureido sugars via carbodiimides and their conformational behaviour in water

The preparation of sugar ureas and thioureas by nucleophilic addition of water or hydrogen sulfide, respectively, to sugar-derived carbodiimides has been examined. Acetic acid efficiently catalysed the formation of ureas, whereas silica gel was found to be a more convenient catalyst in the case of the thioxo analogues. The procedures have been exploited in the development of an amine- and isocyanate-free synthesis of urea- and thiourea-tethered pseudooligosaccharides via the corresponding glycosylcarbodiimido sugars. The fully unprotected compounds adopted, preferentially, the (Z,Z) configuration at the pseudoamide bonds in water solution.

A glycosylation protocol based on activation of glycosyl 2-pyridyl sulfones with samarium triflate

[reaction--see text] Reaction of glycosyl 2-pridyl sulfones (e.g.,2) with alcohols and samarium(III) triflate affords glycosides in moderate to excellent yields. Benzylated sulfones can be activated in preference to their benzoylated counterparts, and the methodology has been used to prepare di- and trisaccharides containing both furanose and pyranose residues. Thioglycosides do not react under these conditions, and the sulfones are inert to the N-iodosuccinimide/silver triflate promoter system commonly used to activate thioglycosides. This selectivity allowed the efficient preparation of oligosaccharides via orthogonal glycosylation protocols.

Inhibition of neuraminidase with neuraminic acid C-glycosides

Neuraminic (sialic) acid based alpha-C-glycosides have been synthesized and their inhibitory activity towards bacterial neuraminidase (sialidase) was examined. While some C-glycosides were found to be potent inhibitors (Ki 15-30 microM) of this neuraminidase, others afforded no measurable activity. The structure-activity relationship of these C-glycosides is discussed in the context of other previously reported sialidase inhibitors.

Spirostanols obtained by cyclization of pseudosaponin derivatives and comparison of anti-platelet agglutination activities of spirostanol glycosides

Naturally occurring saponins 3 and 4 have a normal type F ring and alpha-arranged CH(3)-21 group. Treatments of pseudosaponin peracetates 18 and 19 derived from 3 and 4, respectively, with alcoholic KOH, followed by acidification with acetic acid, gave spirostanols 20 and 22 having iso type F rings as major products. Structural analyses of sapogenins and saponins derived from pseudo derivatives 11, 12, 18 and 19 were performed by comparisons of their 1H-NMR spectral data and the X-ray analytical data of 3-O-p-bromobenzoyl sarsasapogenin 7, 3-O-acetyl diosgenin 13 and saponin 20. The mechanisms of ring-closure reaction of the side chain at C-22 of pseudosapogenins and pseudosaponins were deduced using stereomodels of the spirostanols derived from 11 under various reaction conditions. Inhibitory activities of saponin diglycosides 3, 4, 20, 21 and 25 on human platelet agglutinations induced by ADP and ristocetin were compared.

Synthesis of the C-glycoside analogue of a novel sialyl Lewis X mimetic

Sialyl Lewis X (sLex) mimetics that can function as selectin antagonists have received considerable attention in connection with the development of novel antiinflammatory therapies. An interesting structure that emerged from the studies of the Wong group is the 1,1-Gal-Man disaccharide 2, reported to bind E-selectin 5 times more strongly than sLex. The C-glycoside derivative 3 is of interest both as a conformational probe for selectin binding and as a hydrolytically stable analogue. Herein we illustrate a novel methodology for beta-C-galacto-disaccharides in the synthesis of 3. The protocol has as a key step a novel oxocarbenium ion-enol ether cyclization to give a C1-substituted galactal.

Regioselective synthesis of p-nitrophenyl glycosides of beta-D-galactopyranosyl-disaccharides by transglycosylation with beta-D-galactosidases

The beta-D-galactosidase from porcine liver induced regiospecific transglycosylation of beta-D-galactose from beta-D-Gal-OC6H4NO2-o to OH-6 of, respectively, p-nitrophenyl glycoside acceptors of Gal, GlcNAc and GalNAc to afford beta-Gal-(1-->6)-alpha-Gal-OC6H4NO2-p, beta-Gal-(1--> 6)-beta-Gal-OC6H4NO2-p, beta-Gal-(1-->6)-alpha-GalNAc-OC6H4NO2-p, beta-Gal-(1-->6)-beta-GalNAc-OC6H4NO2-p, beta-Gal-(1-->6)-alpha-GlcNAc-OC6H4NO2-p, and beta-Gal-(1-->6)-beta-GlcNAc-OC6H4NO2-p. The enzyme showed much higher transglycosylation activity for the alpha-glycoside acceptors than the corresponding beta-glycoside acceptors. The regioselectivity of the beta-D-galactosidase from Bacillus circulans ATCC 31382 greatly depended on the nature of the acceptor. When alpha-D-GalNAc-OC6H4NO2-p and alpha-D-GlcNAc-OC6H4NO2-p were used as acceptors, the enzyme showed high potency for regioselective synthesis of beta-Gal-(1-->3)-alpha-GalNAc-OC6H4NO2-p and beta-Gal-(1-->3)-alpha-GlcNAc-OC6H4NO2-p in high respective yields of 75.9 and 79.3% based on the acceptors added. However, replacement of beta-D-Gal-OC6H4NO2-p by beta-D-GalNAc-OC6H4NO2-p did change the direction of galactosylation. The enzyme formed regioselectively beta-Gal-(1-->6)-beta-Gal-OC6H4NO2-p with (beta-Gal-1-->(6-beta-Gal-1-->)n6-beta-Gal-OC6H4NO2-p, n = 1-4). No beta-(1-->3)-linked product was detected during the reaction. Use of the two readily available beta-D-galactosidases facilitates the preparation of (1-->3)- and (1-->6)-linked disaccharide glycosides of beta-D-Gal-GalNAc and beta-D-Gal-GlcNAc.

Nucleic acid components and their analogues: new synthesis of bicyclic thiopyrimidine nucleosides

A novel synthesis of condensed bicyclic thiopyrimidine glycosides utilising 1H-cyclopentapyrimidine-2(3H)-thiones and alpha-bromoglucose or alpha-bromogalactose tetraacetate as starting components is described.

Thermal C-glycosylation of D-glucal with trimethylsilyl cyanide

The treatment of 3,4,6-tri-O-acetyl-D-glucal and unprotected D-glucal with trimethylsilyl cyanide, under thermal conditions in the absence of catalyst, afforded the corresponding 2,3-unsaturated glycosyl cyanides in high yield.

A de novo synthesis of 2,6-dideoxy-C-aryl glycosides based on ring closing metathesis and diastereoselective epoxide cleavage/anomerization reactions

[formula: see text] This paper describes a synthesis of enantiomerically pure 2,6-dideoxy-C-aryl glycosides, starting from non-carbohydrate precursors. The synthesis starts from homoallylic alcohols (obtained in enantiomerically pure form by enzymatic resolution), which are elaborated to dihydropyrans using ring closing metathesis as the key step. Epoxidation and epoxide cleavage complete the synthesis. The stereochemical outcome of the sequence depends on the conditions of the epoxide cleavage reaction.

Preparation of a new carboranyl lactoside for the treatment of cancer by boron neutron capture therapy: synthesis and toxicity of fluoro carboranyl glycosides for in vivo 19F-NMR spectroscopy

The synthesis of new ortho-carboranyl lactosides 8, 17, 19 and glucosides 22 and 23 for the use in boron neutron capture therapy is reported. Carboranyl lactosides 17 and 19 as well as the glucosides 22 and 23 contain a fluorine atom to allow a noninvasive determination of these compounds in tumor cells by 19F-NMR spectroscopy. In cloning efficiency tests on human bronchial carcinoma cells the carboranyl lactosides 17 and 19 displayed almost no cytotoxicity. Thus, the considerably cytotoxic carboranyl alcohol 11 is detoxified when linked to a sugar moiety such as in carboranyl glucoside 22.

[Synthesis of disaccharide Neu5Gcalpha(2-6)GalNAcalpha as a spacer glycoside]

The first synthesis of the Neu5Gc analogue of SiaTn disaccharide, which can be detected in breast tumors by immunochemical methods, is reported. The regioselective sialylation of (3-trifluoroacetamidopropyl)-2-azido-2-deoxy-alpha-D-galactopyranoside with peracetate of the methyl ester of N-acetoxyacetylneuraminic acid beta-ethylthioglycoside in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid (or its trimethylsilyl ester) resulted in the derivatives of alpha- and beta-sialyl(2-->6)galactosaminide in 39 and 32% yields, respectively. The catalytic hydrogenolysis of the azido group and subsquent N- and O-acetylation of the alpha-anomer gave the trifluoroacetamidopropyl glycoside peracetate. Removal of the protective groups led to glycoside Neu5Gc alpha(2-->6)GalNAc alpha-O(CH2)3NH2. Using the Neu5Gc derivative with acetoxyacetyl groups at positions O9 and O4 as a donor increases the alpha-selectivity of sialylation to afford the alpha- and beta-anomers in 69 and 8% yields, respectively.

Reductive aromatization of quinols: synthesis of the C-arylglycoside nucleus of the papulacandins and chaetiacandin

[reaction: see text] Nucleophilic 1,2-addition of lithiated glycal 9b to functionalized quinone 7 provided, after reductive aromatization, C-arylglycoside 11b. Treatment with mCPBA afforded the tricyclic papulacandin framework. Alternatively, hydroboration gave the chaetiacandin nucleus.

Novel Mn(II)Mn(III)Mn(II) trinuclear complexes with carbohydrate bridges derived from seven-coordinate manganese(II) complexes with N-glycoside

Reactions of MnX2.nH2O with tris(N-(D-mannosyl)-2-aminoethyl)amine ((D-Man)3-tren), which was formed from D-mannose and tris(2-aminoethyl)amine (tren) in situ, afforded colorless crystals of [Mn((D-Man)3-tren)]X2 (3a, X = Cl; 3b, X = Br; 3c, X = NO3; 3d, X = 1/2SO4). The similar reaction of MnSO4.5H2O with tris(N-(L-rhamnosyl)-2-aminoethyl)amine ((L-Rha)3-tren) gave [Mn((L-Rha)3-tren)]SO4 (4d), where L-rhamnose is 6-deoxy-L-mannose. The structures of 3b and 4d were determined by X-ray crystallography to have a seven-coordinate Mn(II) center ligated by the N-glycoside ligand, (aldose)3-tren, with a C3 helical structure. Three D-mannosyl residues of 3b are arranged in a delta(ob3) configuration around the metal, leading to formation of a cage-type sugar domain in which a water molecule is trapped. In 4d, three L-rhamnosyl moieties are in a delta(lel3) configuration to form a facially opened sugar domain on which a sulfate anion is capping through hydrogen bonding. These structures demonstrated that a configurational switch around the seven-coordinate manganese(II) center occurs depending on its counteranion. Reactions of 3a, 3b, and 4d with 0.5 equiv of Mn(II) salt in the presence of triethylamine yielded reddish orange crystals formulated as [[Mn((aldose)3-tren)]2Mn(H2O)X3.nH2O (5a, aldose = D-Man, X = Cl; 5b, aldose = D-Man, X = Br; 6d, aldose = L-Rha, X = 1/2SO4). The analogous trinuclear complexes 6a (aldose = L-Rha, X = Cl), 6b (aldose = L-Rha, X = Br), and 6c (aldose = L-Rha, X = NO3) were prepared by the one-pot reaction of Mn(II) salts with (L-Rha)3-tren without isolation of the intermediate Mn(II) complexes. X-ray crystallographic studies revealed that 5a, 5b, 6c, and 6d have a linearly ordered trimanganese core, Mn(II)Mn(III)Mn(II), bridged by two carbohydrate residues with Mn-Mn separations of 3.845(2)-3.919(4) A and Mn-Mn-Mn angles of 170.7(1)-173.81(7) degrees. The terminal Mn(II) atoms are seven-coordinate with a distorted mono-face-capped octahedral geometry ligated by the (aldose)3-tren ligand through three oxygen atoms of C-2 hydroxyl groups, three N-glycosidic nitrogen atoms, and a tertiary amino group. The central Mn(III) atoms are five-coordinate ligated by four oxygen atoms of carbohydrate residues in the (aldose)3-tren ligands and one water molecule, resulting in a square-pyramidal geometry. In the bridging part, a beta-aldopyranosyl unit with a chair conformation bridges the two Mn(II)Mn(III) ions with the C-2 mu-alkoxo group and with the C-1 N-glycosidic amino and the C-3 alkoxo groups coordinating to each metal center. These structures could be very useful information in relation to xylose isomerases which promote aldose-ketose isomerization by using divalent dimetal centers such as Mn2+, Mg2+, and Co2+.

Preparation of 5-(2,6-dideoxy-2-fluoro-alpha-L-talopyranosyloxy)-6-hydroxynap htho[2,3- f]quinoline-7,12-dione (FT-Alz), a new-type, potentially antitumor substance with various biological activities

The title compound (6), its structure being imaginatively created, has been prepared through coupling of alizarine blue (2), a classical dye, and 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl bromide (3). Compound 6 has considerably higher and different antitumor activity from that of doxorubicin or its analogue (10), and, further, has properties to reverse multidrug resistance (by P-glycoprotein), to inhibit topoisomerase II, and to induce apoptosis.