Radical-mediated synthesis of alpha-C-glycosides based on N-acyl galactosamine

[structure] C-Glycosides of N-acyl 2-amino-2-deoxygalactose (acyl = MeCO, CF(3)CO, t-BuOCO) are available in a stereoselective manner by trapping of an anomeric radical with an activated alkene. Using anomeric selenides, radical generation and trapping is carried out under conditions that avoid competitive reduction, and this chemistry has been applied to the synthesis of the novel C-glycoside analogue of O-benzyl alpha-D-GalNAc.

Synthesis of 3-O-sulfoglucuronyl lacto-N-neotetraose 2-aminoethyl glycoside and biotinylated neoglycoconjugates thereof

The 2-aminoethyl glycoside of pentasaccharide 3-O-sulfo-GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1--> 4)Glc(beta (1) and its conjugates with biotin and biotinylated polyacrylic acid were synthesized as molecular probes to investigate the recognition of the HNK-1 epitope containing carbohydrates by proteins. Key steps in the first of two investigated schemes for the preparation of the target compound 1 were (a) assembling of the pentasaccharide backbone (compound 10) by glycosylation of selectively substituted allyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta with glucuronyl-galactose glycosyl donor, (b) transformation of the allyl aglycon in 10 into 2-azidoethyl one (to give 11), (c) selective deprotection of the OH group at C-3 of the GlcA residue in 11 via saponification, intramolecular formation of 6,3-lacton (13) and its methanolysis, and (d) subsequent O-sulfation. The alternative scheme with the use of 2-azido-ethyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta instead of the allyl glycoside 6 was less effective due to smaller yield at the step of pentasaccharide synthesis. Additionally to 1 the 2-aminoethyl glycosides of the oligosaccharides GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta, 3-O-sulfo-GlcA(beta-1-->3)Gal(beta, and GlcA(beta-1-->3)Gal(beta were also synthesized.

Azido glycoside primer: a versatile building block for the biocombinatorial synthesis of glycosphingolipid analogues

A lactoside primer, 12-azidododecyl beta-lactoside, was synthesized via the Koenigs-Knorr method by glycosylation of 1,12-dodecyldiol with perbenzoylated lactosyl bromide. The presence of the 2-O-acyl substituent in the donor gave the beta-lactoside, and an excess of acceptor ensured monoglycosylation of the diol. Mesylation of the omega-hydroxyl group in the aglycon, followed by displacement of the mesylate with azide and subsequent O-debenzoylation gave the desired omega-azidododecyl beta-lactoside. The azido glycoside primer was examined in mouse B16 melanoma cells for its feasibility as a building block for oligosaccharide biosynthesis. Uptake of the azido glycoside primer by B16 cells resulted in the sialylation of the galactose residue of the primer to give a glycosylated product having the same glycan as in ganglioside GM3. After 24 h incubation of B16 cells with the primers, the amount of sialylated omega-azidododecyl beta-lactoside primer was 75% of the amount of sialylated n-dodecyl beta-lactoside. However, after 48 h incubation, both primers gave equal amounts of the sialylated products. Interestingly, the remaining azido glycoside primer after 48 h incubation was 5.6-fold greater than that of the alkyl primer, indicating degradation of the alkyl primer to a larger extent than the omega-azido glycoside primer. The facile chemical synthesis and the efficient uptake in cells make the azido glycoside primer a versatile building block for the biocombinatorial synthesis of glycolipid oligosaccharides.

The application of the intermediate 2-methyl-glyco-[2,1-d]-2-oxazolines for glycoside synthesis

The synthesis of 2-acylamino-2-deoxysugars 1,2-trans-glycosides is described via the oxazolinium salt generated from an O,N-acetylated 1,2-cis-glycosyl halide of 2-amino-2-deoxysugar under the conditions of halide-anion catalysis. This salt was then interacted with alcohol to form the corresponding 1,2-trans-glycoside. A method for removing the generated hydrogen chloride is described. The conditions of this synthesis allow glycosides with acid-labile functional groups to be obtained. Suppression of the anomerisation of 1,2-trans-glycosides was achieved by the introduction of N,N'-dicyclohexyl urea into the reaction medium.

Synthesis and structure of 4-O,6-O-glycosylidene glycosides

Interglycosidic spiro ortho esters (9-20) were efficiently prepared from methyl 2,6-di-O-benzylgluco- or galactopyranoside and various sugar lactones in the presence of methoxytrimethylsilane and a catalytic amount of trimethylsilyl triflate. All of the prepared sugar ortho esters possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d][1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurations of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally caused from that between the spiro ring systems in their molecules in each case.

Development of an efficient, regio- and stereoselective route to libraries based on the beta-D-glucose scaffold

The design and execution of an efficient synthetic route for the sequential functionalization of the five hydroxyl substituents of beta-D-glucose has been achieved. This strategy, based on the stereoselective glycosidation of thioglycosides, provides a new approach for the parallel construction of a wide variety of beta-D-glucose analogues and as such holds promise for solid-support library syntheses.

Chemical and enzymatic synthesis of glycopolymers

The development of efficient, fast, flexible and general synthetic routes to glycopolymers is an ongoing challenge and much progress has been made in recent years. Chemical coupling methods have become increasingly sophisticated to fine-tune reactivity of reagents by fortuitous choices of anomeric activating group and protecting groups. As a result, oligosaccharide synthesis has become more predictable and reliable even to the extent that first examples of saccharide library syntheses in solution and on the solid phase have been published. In biology, the repertoire of biocatalysts that can be used for glycoside synthesis is ever-increasing, and enzyme-catalysed glycosylation steps have been successfully incorporated into synthetic strategies.

A highly stereoselective construction of beta-glycosyl linkages by reductive cleavage of cyclic sugar ortho esters

The preparation of beta-glycosides by the reductive cleavage of spiro sugar ortho esters is described in this report. This procedure is based on a concept completely different from those of other methods for glycosylation. Twelve sugar ortho esters that commonly possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d][1,3]dioxin] ring systems in their molecules were reduced by LiAlH(4)/AlCl(3) or NaCNBH(3)/AlCl(3). Among these ortho esters, those (9a-12a) prepared from the D-sugar lactones (1-4) and 2, 3-di-O-benzyl-alpha-D-glucopyranoside (7) or those (19a, 20a) prepared from the L-sugar lactones (5, 6) and 2, 3-di-O-benzyl-alpha-D-galactopyranoside (8) were selectively converted into beta-(1 --> 4)-glycosides (9b-12b or 19b, 20b) in excellent yields by the treatment of LiAlH(4)/AlCl(3). In contrast, the ortho esters (13a-16a or 17a, 18a) that were prepared from combinations of the D-sugar lactones and 8 or those of the L-sugar lactones and 7 were efficiently reduced with NaBH(3)CN/AlCl(3) to afford beta-(1 --> 6)-glycosides (13b-16b or 17b, 18b) selectively. It was remarkable that the resulting disaccharides were obtained with extremely high beta-selectivity even in the cases with mannosyl or rhamnosyl glycosides. Moreover, these products would be useful units for the construction of branched saccharides, because the newly formed hydroxy groups could be again glycosylated without further deprotection procedures. The high regio- and stereoselectivity was totally explained by considering the structures and the conformations of these ortho ester molecules and the stereoelectoronic effects of their spiro ring systems. In addition, the preparation of the sugar ortho esters with glucosamine derivatives and the reactivity of these ortho esters are described in this report. N-Phthaloyl glucosamine derivatives (21, 22) were efficiently reacted with the benzyl-protected gluconolactone (1) in the presence of TMSOMe and TMSOTf to afford ortho esters (23a-c). After the conversion of the phthalimido functionality to the dibenzyl amino group, glucosylideneglucosamine (25) was reduced with LiAlH(4)/AlCl(3) to afford beta-(1 --> 4)-glycoside (26) selectively.

Formation of beta-glucosamine and beta-mannose linkages using glycosyl phosphates

[reaction: see text] Glycosyl phosphates were examined for their utility in the synthesis of challenging glycosidic linkages. beta-Glucosamine glycosides were formed preferentially and in good yield. beta-Mannosides were constructed in high overall yield with modest anomeric selectivity. Interesting solvent and conformational influences on the stereochemical outcome of the coupling reactions were observed.

The cyanation reaction of O-acetylated S-glycosyl phosphorothioates

The reaction of alpha- and beta-1-S-phosphorothioates of per-O-acetylated monosaccharides (galactose, xylose, glucose) with trimethylsilyl cyanide in the presence of boron trifluoride etherate has been investigated. It has been established that in dichloromethane 1,2-O-cyanoethylidene derivatives of aldoses are formed in high yields. When the reaction was carried out in acetonitrile, peracetylated galactosyl cyanide was formed as the major product.

N-Glycosidation of D-arabino-hex-2-ulosonic acid

Two approaches to N-functionalized D-arabino-hex-2-ulosonic acid derivatives were established by nucleophilic substitution of methyl (3,4,5-tri-O-acetyl-beta-D-arabino-hex-2-ulopyranosyl)onate bromide (1). Reaction of 1 with amino compounds in the presence of mercury(II) cyanide led to the 2,3-cis configured beta-D-arabino N-glycosides. On the other hand, the reaction of bromide 1 with azide, followed by catalytic hydrogenation led to 2,3-trans alpha-D-arabino glycosyl amine methyl 3,4,5-tri-O-acetyl-2-amino-alpha-D-arabino-hex-2-ulopyranosonate, which was easily rearranged to the thermodynamically more stable beta-D-arabino N-acetyl derivative methyl 4,5-di-O-acetyl-2-acetylamino-3-hydroxy-beta-D-arabino-hex-2-ulopyranosonate. The assignment of configuration of the tertiary anomeric centre and conformation of all products was based on 1H NMR H,H coupling constants and NOE difference experiments.

Preparation, chemical and crystal structures of N-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)pyridinium chloride

Preparation and isolation of N-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)pyridinium chloride are described. Its structure was determined by 1H NMR spectroscopy and X-ray analysis. X-ray crystallography revealed that the salt crystallizes with one molecule of water. Ab initio calculations were used to determine charges on atoms in the cation of the title compound.

Analysis of glycosidically bound aroma precursors in tea leaves. 1. Qualitative and quantitative analyses of glycosides with aglycons as aroma compounds

Twenty-six synthetic glycosides constituting aglycons of the main tea aroma compounds ((Z)-3-hexenol, benzyl alcohol, 2-phenylethanol, methyl salicylate, geraniol, linalool, and four isomers of linalool oxides) were synthesized in our laboratory as authentic compounds. Those compounds were used to carry out a direct qualitative and quantitative determination of the glycosides as aroma precursors in different tea cultivars by capillary gas chromatographic-mass spectrometric (GC-MS) analyses after trifluoroacetyl conversion of the tea glycosidic fractions. Eleven beta-D-glucopyranosides, 10 beta-primeverosides (6-O-beta-D-xylopyranosyl-beta-D-glucopyranoside) with aglycons as the above alcohols, and geranyl beta-vicianoside (6-O-alpha-L-arabinopyranosyl-beta-D-glucopyranoside) were identified (tentatively identified in the case of methyl salicylate beta-primeveroside) in fresh tea leaves and quantified on the basis of calibration curves that had been established by using the synthetic compounds. Primeverosides were more abundant than glucosides in each cultivar we investigated for making green tea, oolong tea, and black tea. Separation of the diastereoisomers of linalool and four isomers of linalool oxides by GC analyses is also discussed.

The intermolecular migration of polyol stannylenes as a reaction contributing to the regioselectivity of substitution

Pairs of the partially protected glycosides benzyl 4,6-O-benzylidene-beta-D-galactopyranoside, benzyl 2,3-di-O-benzyl-beta-D-galactopyranoside, benzyl 2,6-di-O-benzyl-alpha-D-galactopyranoside, and benzyl 2,3-di-O-benzyl-alpha-D-glucopyranoside were treated with equimolar proportions of Bu2SnO in benzene in the conditions of stannylene formation, and the resulting mixture was benzoylated in situ with benzoyl chloride. Estimation of the product of benzoylation led to the following order of reactivity in the stannylenation reaction: 2,3-diol > 4,6-diol, and 2,3-diol > 3,4-diol. An intermolecular migration of dibutyltin between sugars was demonstrated. It is considered that these migrations contribute efficiently to the regiospecificity of the stannylene reaction.

Synthesis and amphiphilic properties of glycosyl-1,4-benzodiazepin-2,5-diones

Glycosyl-1,4-benzodiazepin-2,5-diones were prepared by coupling polyhydroxylated groups at N-1 of the corresponding benzodiazepine. The groups include 1-deoxy-D,L-xylit-1-yl, 6-deoxy-D-glucopyranos-6-yl, and 6-deoxy-3-OR-D-glucopyranos-6-yl (R = n-CnH(2n +1); n = 8, 12, and 16). The structural variations of the sugar group allowed comparison of such amphiphilic data as water solubility (Sw), critical micelle concentration (CMC), and corresponding surface tension (gamma) values. At 25 degrees C, unsubstituted benzodiazepines have Sw values from 0.9 to 4.2 10(-3) mol L(-1), whereas xylit-1-yl and 6-deoxy-D-glucopyranos-6-yl derivatives are, respectively, 7.4-25 and 58-204 times more soluble. Also, compounds with R = n-C8H17 are more soluble than corresponding benzodiazepines (1.4-5.8 times) and give micelles with CMC from 2.7 to 5.6 10(-3) mol L(-1) and corresponding gamma from 29 to 37 mN m(-1). In contrast, compounds with R = n-C12H25 and n-C16H33 are not soluble enough to reach the critical micelle concentration.

Heterocyclic derivatives of sugars: the formation of 1-glycosyl-3-methylpyrazol-5-ones from hydrazones

Conditions to effect the conversion of monosaccharide and disaccharide hydrazones to 1-glycosyl-3-methylpyrazol-5-ones were examined. The sugar pyrazolone derivatives were sensitive to oxidation, but high yields were achieved with 2,2,2-trifluoroethyl acetoacetate in mildly acidic solution. Azo coupling of the pyrazolones produced highly coloured azopyrazolone derivatives that prevented further degradation, and these may prove useful labels for chromatographic analysis of carbohydrates.

Stereoselective synthesis of the alpha-glycoside of a KDO "C"-disaccharide

The reaction of tert-butyl (4,5,7, 8-tetra-O-acetyl-3-deoxy-alpha-D-manno-2-octulopyranosyl chloride)onate donor 7 with the 6-formylgalactopyranoside acceptor 4 in the presence of SmI(2) provided only the KDO alpha-C-disaccharide 8. The bulky tert-butyl ester in the donor was used to reverse the stereochemical outcome of C-glycosylation, stereoselectively forming the alpha-"C"-disaccharide of KDO.

Novobiocin-related compounds: synthesis of 3-benzoylamino-2-oxo-2H-1-benzopyran-7-yl D-glycopyranosides by the trichloroacetimidate methodology

A general stereoselective method for the synthesis of 4-deoxynovobiocin-related glycosides is described. 3-Benzoylamino-2H-1-benzopyran-7-yl 2,3,4,6-tetra-O-acetyl-D-glycopyranosides of glucose, galactose and mannose were synthesised from appropriate O-glycosyltrichloroacetimidates and N-(7-hydroxy-2-oxo-2H-1-benzopyran-3-yl)benzamides in boiling methylene chloride in the presence of boron trifluoride etherate. Heating of these products in a mixture of triethylamine and methanol gave the corresponding deprotected 3-benzoylamino-2-oxo-2H-1-benzopyran-7-yl beta-D-glycopyranosides.

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.

The synthesis of diosgenyl 2-amino-2-deoxy-beta-D-glucopyranoside hydrochloride

The N-trifluoroacetyl- and N-tetrachlorophthaloyl-protected bromide of D-glucosamine has been used for the first time as a glycosyl donor for the glycosylation of diosgenin [(25R)-spirost-5-en-3beta-ol]. Both 1,3,4,6-tetra-O-acetyl-2-deoxy-2-trifluoroacetamido-beta-D-glucopy ranoside and 1,3,4,6-tetra-O-acetyl-2-deoxy-2-tetrachlorophthalimido-alpha,beta -D-glucopyranoside were transformed into the appropriate glycosyl bromides. These reacted with diosgenin under mild conditions, using silver triflate as a promoter, and gave the corresponding protected diosgenyl glycosides. Each was deprotected to give diosgenyl 2-amino-2-deoxy-beta-D-glucopyranoside hydrochloride. The structures of the new glycosides were established by 1H NMR spectroscopy.

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.