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Generally, glycosylation reactions activate an anomeric substituent in a glycosyl donor to generate an oxocarbenium ion intermediate. Here we report a novel glycosylation reaction triggered by the activation of a 2-O-substituted propargyl group in a 3,6-O-1,1′-[(ethane-1,2-diyl)bibenzene-2,2′-bis(methylene)]-β-thioglucoside. This reaction proceeds through a cationic Au(I)-mediated intramolecular migration of the anomeric substituent onto the alkyne moiety of the propargyl group, followed by α-attack by the hydroxy group in the glycosyl acceptor on the oxocarbenium ion. The migration of the anomeric group occurs selectively through a 6-exo-dig pathway. The 2-(phenylsulfanyl)prop-2-en-1-yl group produced during the glycosylation is removable under conditions similar to those used for removing an allyl group. This reaction will be developed for further applications in orthogonal oligosaccharide synthesis.

A 3,5-didocosyloxybenzyl alcohol tag that was introduced at the anomeric position of the carbohydrate acceptor was applied in the assembly of a pentasaccharide. The intrinsic high solubility in nonpolar solvent and precipitation properties in polar solvent are crucial features of this tag. Thus, rapid and simple precipitation-centrifugation can be conducted throughout the synthetic route at each step to ease work-up and purification processes, and reduce the amount of solvent required. This method provides an efficient, environmental-friendly, and economical approach to synthesize complex oligosaccharides.

The palladium-catalyzed one-pot synthesis of 2,3-deoxy-3-keto aryl C-glycosides is achieved from glycals and anilines in the presence of tert-butyl nitrite and aqueous HBF4 under mild conditions. This one-pot method stereospecifically provides α- and β-aryl glycosides (≥19:1 by NMR) in good yields at room temperature. The configuration at the C-3 position in the glycal determines the anomeric selectivity (i.e., α or β) of the desired products.

In this letter, we report an approach to the stereoselective α-glycosylation of l-fucose that is exemplified by effect of anomeric configuration. The neighboring group participation is not compatible with α-glycosylation of l-fucose, therefore the remote participation by 4-O-Bz was employed to control the formation of 1,2-cis-glycosidic bond. Furthermore, we found the anomeric configuration of fucose donor is crucial to stereoselectivity of the glycosylated products. The α/β-mixed products were generated by using β-anomeric donor while the glycosyl donor in α configuration yielded products in high α-selectivity possibly due to the distinct pathway to forming the key intermediates. This phenomenon supplies the basis for the synthesis of complicated natural carbohydrates containing fucose α-glycoside, such as fucoidans, fucosylated N-glycans, and fucosylated chondroitin sulfates, etc.

Periploside A is the prototypical congener of the pregnane glycosides occurring in the Chinese medicinal plant Periploca sepium, featuring a unique seven-membered formyl acetal bridged spiro-­orthoester (FABO) sugar linkage and potent immunosuppressive activities. This account details our efforts on the stereoselective construction of the FABO motif that has led to a successful total synthesis of peri­ploside A.1 Introduction2 Attempts at Construction of the FABO Motif2.1 Intermolecular Condensation and Transacetalation2.2 Intramolecular Hydrogen Atom Transfer (HAT) Reaction3 Synthesis of the FABO Motif Bearing the Unnatural Anomeric Configuration4 Synthesis of the FABO Motif Bearing the Natural Anomeric ­Configuration4.1 Unsuccessful Attempts4.2 Final Solution5 Conclusion

A series of 1,5-anhydro- d - glycero - d - gluco -heptitol derivatives have been prepared from 3- O -benzyl-1,2- O -isopropylidene- d - glycero - d - gluco -heptofuranose via conversion into anomeric bromide and thiophenyl derivatives, followed by glycal formation and reductive desulfurization, respectively. Global deprotection of the protected intermediates afforded the 1,5-anhydro derivatives of the d - glycero - d - gluco - and 1,2-dideoxy- d - altro - configuration as well as the 1,5-anhydro-2-deoxy- d - altro -hept-1-enitol. In addition, the 7- O -phosphorylated d - glycero - d - gluco -heptose and its 1,5-anhydro analogue were prepared in good yields utilizing phosphoramidite chemistry. A novel heptitol analogue based on a 1-deoxynojirimycin scaffold was also elaborated via a Wittig­-type chain elongation followed by dihydroxylation, separation of the resulting epimers, and global deprotection. The target compounds, however, were not active as inhibitors of the bacterial sedoheptulose-7-phosphate isomerase GmhA.

Aryl C-glycosides are common structural motifs found in bioactive natural products and commercially available drugs. Despite their importance, most chemical methods to prepare C-glycosides have relied on the nucleophilic addition/substitution of a glycosyl electrophile, which result in variable anomeric selectivities and yields. Furthermore, these methods are not compatible with saccharides containing free hydroxyl groups. Here, we describe a direct cross-coupling reaction of anomeric nucleophiles (anomeric stannanes) and aryl halides. This method is the first general approach to the synthesis of aryl C-glycosides resulting in exclusive anomeric selectivities for both anomers for a broad range of aryl and carbohydrate coupling partners (including unprotected saccharides).1 Introduction2 Synthesis of Anomeric Stannanes3 Glycosyl Stille Cross-Coupling4 Future Outlook5 Summary

The reactivity of trifluoromethanesulfonyl esters derived from l-lyxofuranosides and l-lyxopyranosides was investigated with various 5-aminopyrimidines as nucleophiles with the expectation to synthesize N-substituted 5-amino-ribosugars. The lyxopyranoside forms were found to be unreactive, while the lyxofuranoside forms were found to be reactive with 5-aminopyrimidines, yielding novel N-substituted 5-amino-lyxofuranosides. We report on the synthesis of these novel N-substituted lyxofuranosides and the systematic analyses of NMR data that demonstrate trends within each series: furano-, pyrano-, β- and α- anomers of l-lyxose and β-d-ribopyranoside forms. The data call for caution when identifying these monosaccharides in isomeric mixtures.

Adopting the ‘remote activation concept’ toward stereocontrolled glycoside synthesis with minimal use of protection groups, a general synthesis of phenolic 1,2- cis glycopyranosides is reported, as exemplified by aryl α- d -galacto-, α- d -gluco- and 2-azido α- d -glucopyranosides among others using glycosyl donors bearing an anomeric (3-bromo-2-pyridyloxy) group and catalyzed by methyl triflate.

The pyranoside-into-furanoside (PIF) rearrangement was recently reported as a useful tool for the synthesis of furanoside-containing complex oligosaccharides. Until now, this transformation has only been described for some protected allyl-β- d -galactosides and one l -fucoside. In this communication its applicability is expanded. The formation of furanosides was observed under acid-promoted sulfation for a series of galactosides with varying alkyl substituents at the anomeric position as well as for several fucosides and glucosides. Meanwhile, furanoside formation was not detected in the case of mannopyranosides. The different reactivity of substrates was explained by values of activation barriers of endocyclic C1–O5 bond cleavage calculated by ab initio RHF methods. The reported results clarify the scope and limitations of the PIF rearrangement, which is important for its application in the synthesis of carbohydrate structures of practical meaning.

A mild, efficient and diastereoselective gold- and silver-catalyzed O-glycosylation with pyranone glycosyl donors is described. The reactions led to the formation of α-anomers in up to 91% yield with good diastereoselectivities.

An efficient synthesis of the pentasaccharide repeating unit of the O-antigen of Escherichia coli O36 is reported. A stereoselective [2 + 3] block glycosylation method has been exploited to obtain the target pentasaccharide derivative using thioglycoside, trichloroacetimidate, and halide-exchange glycosylation procedures. The 2-azidoethyl group has been used as the anomeric protecting group to make the glycone moiety with a readily available linker for its conjugation to a protein without destroying the cyclic structure at the reducing end. Yields were high in all the intermediate steps.

Various acceptors including carbohydrates, amino acids, natural products, and hydroxylamine derivatives were coupled with 3,4,6-tri-O-acetyl- d -glucal in the presence of Cu(OTf)2 as catalyst. The protocol offers facile and efficient Ferrier glycosylation for the synthesis of 2,3-unsaturaed O-glycosides in good yields and high anomeric selectivity.

After a quick review of the existing methods that enable the quaternarization of the anomeric position of carbohydrates via a C–H bond functionalization process, we summarize recent contributions from our group related to the preparation of α- and β-ketopyranosides by the 1,5-insertion of metal carbenes. 1 Introduction 2 Early Developments: Anchoring of Reactive Species at the Anomeric Position 2.1 Radical-Promoted Quaternarization of the Anomeric Position 2.2 Photochemically Induced Quaternarization of the Anomeric Position 2.3 Alkylidene-Promoted Quaternarization of the Anomeric Position 2.4 Nitrene-Promoted Quaternarization of the Anomeric Position 2.5 Any Possible Extension to the Preparation of α- and β-Ketopyranosides? 3 Carbene-Mediated Functionalization of the Anomeric C–H Bond of Carbohydrates 3.1 Functionalization of Carbohydrate Scaffolds by the Insertion of Metal Carbenes: A Challenging Task 3.2 Preparation of Carbene Precursors 3.3 Transition Metal Catalyzed Decomposition of Diazo Sugars 3.4 Dramatic Effects of Molecular Sieves 3.5 Ring Opening of γ-Lactones 4 Development of a Stereoselective Glycosylation/Diazo Transfer/Quaternarization Sequence 4.1 Preliminary Studies with a Permethylated Acceptor 4.2 Stereoselective Access to Quaternary Disaccharides: Scope and Limitations 5 Concluding Remarks

A sugar aldehyde with silyl protection at C1, readily prepared from methyl α- d -glucopyranoside, reacted with allylborate or allylchromium reagents to afford the corresponding (anti) adducts, which were selectively converted into either E- or Z-diene. Deprotection of the anomeric position with TBAF proceeded in excellent yield, and further functionalization of the resulting hemiacetal led to the formation of complex bicyclic products such as highly functionalized oxazolidines.

The optimization of rhodium(II) carbene mediated quaternarization of the anomeric position of carbohydrates is reported. Preparation of ketopyranosides in good and reliable yields requires reverse addition of the substrate to a highly diluted suspension of the catalyst in refluxing 1,2-dichloroethane, as well as addition of a carefully controlled amount of molecular sieves, and vigorous stirring. Following these optimized reaction conditions, functionalization of the anomeric position of carbohydrates can finally be performed on a preparative scale.

A novel, highly stereoselective tandem dihydroxylation, hemiketalization and conjugate addition reaction is reported that transforms a linear meso-functionalized bis-enone into a substituted singly anomeric spiroketal, effectively controlling six stereocenters in a single operation. As part of an effort to explore the thermodynamic consequences of establishing the singly anomeric spiroketal in this system, the assembly of a related fully anomeric spiroketal possessing an unusual ketal-spiroketal-ketal framework is demonstrated.

Glucosamine building blocks have been prepared by an efficient regioselective one-pot protection approach. This synthetic route enabled the straightforward preparation of a glucosamine disaccharide in 73% yield. The system Pd(PPh 3 ) 4 /TES was investigated as an alternative procedure for anomeric allyl ether deprotection.

Starting from readily available monosaccharides D-glucose and D-arabinose, a family of novel chiral diene and olefinphosphinite hybrid ligands has been designed. These ligands were prepared by attaching phosphinite or allylic donor sites onto unsaturated carbohydrate scaffolds. In rhodium(I)-catalysed conjugate addition ofboronic acids to enones, the olefin-phosphinite hybrids gave products in up to 99% ee and above, whereas the dienes only led to modest enantioselectivity. However, by shifting the allylic donor sites from position 4 of the pyranose to the anomeric centre, an unexpected reversal of the stereoinduction process was observed.

For the first time, octaglycosylated zinc(II) phthalocya- nines in which the sugar part is protected by acetyl groups and the deprotected zinc(II) phthalocyanines were synthesized and charac- terized. The sugars glucose, galactose, lactose, cellobiose, and mal- tose are anomerically attached either via oxygen or sulfur to the phthalocyanine ring. The necessary starting materials for the syn- theses of the phthalocyanines, the anomerically 4,5-diglycosylated phthalonitriles, were obtained by reacting the anomerically depro- tected sugars containing OH and SH groups with 4,5-difluorophth- alonitrile. The acetyl protected octaglycosylated phthalocyanines were obtained in yields between 55 and 78% by heating the anomer- ically 4,5-diglycosylated phthalonitriles in DMF with hexamethyl- disilazane, p-toluenesulfonic acid, and zinc acetate. The acetyl groups in sugar moieties were removed to afford corresponding water-soluble phthalocyanines.

The reaction of tetra-O-benzylmannosyl trichloroacetimidate with electron-rich phenols in the presence of TMSOTf surprisingly leads to the exclusive formation of aryl β-C-glycosides while a preference for the α-anomer could be observed with other Lewis acids such as ZnCl 2 .

The synthesis of 1,1-disubstituted C-glycosides containing amino and ester containing moieties at what is formally the anomeric site is described. Petasis olefination of pyranosyl lactones provided exo-glycals which underwent regioselective azidoselenation and subsequent radical-mediated C-glycoside formation.

Two new routes to substituted aminotetrahydrofuran derivatives have been investigated. Treatment of 3,6-dihydro-2H-1,2-oxazines with hydrochloric acid in the presence of zinc provided 4-benzylamino-5-hydroxy furanose derivatives which contain a quaternary anomeric centre with a vinyl unit. Upon mesylation and subsequent heating in aqueous media 5-hydroxy-3,4,5,6-tetrahydro-1,2-oxazines were converted into novel bicyclic 1,2-oxazines with complete regio- and stereoselectivity. Cleavage of the N―O bond and subsequent debenzylation furnished enantiopure polyhydroxylated aminotetrahydrofuran derivatives which are promising ligands for selectin inhibition studies.

The first synthesis of the inositol-containing marine glycolipid dioctadecanoyl discoside is reported. The key glycosylation reaction proceeds with β-selectivity at reduced temperature. The separable anomers could be readily progressed to afford discoside, its peracetate and the unnatural β-derivatives.

Chiral room temperature ionic liquids, containing a carbohydrate moiety linked at the anomeric centre to an N-methylimidazolium group have been synthesised. The ionic liquids were prepared in a concise manner and provided ready access to both the D- and L-arabino enantiomers. The same strategy enabled the preparation of D-ribofuranose and D-xylofuranose analogues, in excellent yields.

Herein we report a simple and efficient methodology for the synthesis of thioacetates using benzyltriethylammonium tetrathiomolybdate and acetic anhydride as the key reagents, starting from alkyl halides in a multistep, tandem reaction process. Its application in the synthesis of orthogonally protected cysteine and anomeric β-thioglycosides has also been demonstrated.

A versatile and efficient route to both enantiomers of 4′-quaternary 2′-deoxy-3′- and -4′- EPI-β- C- and - N-nucleosides is described. The asymmetric synthesis involves the SAMP/RAMP--hydrazone α-alkylation methodology and diastereoselective nucleophilic 1,2-additions. Manipulation of the substituents in the anomeric position leads to the thermodynamically more stable β-anomers of excellent diastereo- and enantiomeric purity (

The use of hydroxylamine derivatives as the aminoxy equivalent nucleophiles in Ferrier glycosylation catalyzed by various acid catalysts is described. The reaction of tri-O-protected D-glucal with N-hydroxyphthalimide or N-hydroxysuccinimide was effectively promoted by a catalytic amount of zinc(II) chloride to produce the corresponding aminoxy pseudoglycal in good yields and preferential anomeric selectivity.

This paper describes the synthesis of C- and N-glucopyranosides via trimethylsilyl trifluoromethanesulfonate catalyzed nucleophilic substitution of glucopyranosides, derived from D-glucopyranose, with methyl, ethyl, N-butyl, allyl, benzyl, and phenyl groups at the anomeric carbon centers. Generally, the reactions using allyltrimethylsilane, trimethylsilyl azide, trimethylsilyl cyanide, and 1-phenyl-1-(trimethylsiloxy)ethene as the nucleophiles in the presence of 20 mol% trimethylsilyl trifluoromethanesulfonate in acetonitrile- at -40 °C smoothly proceeded with α-stereoselectivity to afford various C- and N-glucopyranosides in 78-99% yield. Although a decrease in the synthetic yields was observed for some reactions using glucopyranoses with allyl and benzyl groups at the anomeric carbon, the yields could be improved using glucopyranosyl acetates in the presence of 20 mol% trimethylsilyl trifluoro-methanesulfonate in acetonitrile-dichloromethane (1:1) at -78 °C.

The synthesis of two types of triazole-linked glycosyl amino acids, at C-4 and at the anomeric position for mannopyranose and glucopyranose derivatives, respectively, via a copper-catalyzed [3+2] cycloaddition of acetylenic amino acid derivatives and azide-containing glycoside is described.

The trisaccharide 2,3,4-O-tribenzyl-a-L-rhamnosyl- (1→3)-4-O-acetyl-2-O-benzoyl-(1→2)-4-O-acetyl-3-O-benzoyl- a-L-rhamnosyl-1-(4-tolyl)thio-a-L-rhamnopyranoside was pre- pared from the thio-sugar 1-(4-tolyl)thio-a,b-L-rhamnopyranoside from the nonreducing end to the reducing end. The two acceptors possessing 2- and 3-OH groups for the construction of the trisaccha- ride were obtained from a 2,3-benzylidine-protected thio-sugar in a one-pot deprotection manner in a respective ratio of 1:2.5. As do- nors for glycosylation, the thio-sugars of both mono- and disaccha- rides were converted to trichloroacetimido rhamnosides. Through this chemoselective strategy, a trisaccharide was obtained that re- tained an anomeric thio group for coupling with ceramide moieties. Bioassays are in progress.

A series of di- and trisaccharides containing 6-O-linked galactofuranose were synthesized as an anomeric mixture of methyl glycosides using silica-supported perchloric acid.

Enantiopure tert-butyl 4-oxopipecolic esters were converted into cyclic analogues of bishomoaspartic acid and homoglutamic acid by Homer-Wadsworth-Emmons olefination and hydrogenation. Condensation of the side chain carboxylic group with anomeric glucosylamine and suitable protection of the α-amino acid moiety afforded the corresponding N-glucosyl asparagine or glutamine mimetics as useful building blocks in glycopeptidomimetic synthesis.

Due to their high stability, N-glycosyl amides have so far not been considered as glycosyl donors for glycosylation reactions. Two new procedures for the cleavage of the anomeric amide functionality under mild reaction conditions and further stereoselective in situ conversions of the activated glycosyl donors with alcohols and amines to give β-configured O- and N-glycosides are described in this article.

The stereocontrolled synthesis of new carbohydrate-derived acylsilanes with the silylcarbonyl moiety linked to the anomeric carbon via a methylene group is described. Reaction of these acylsilanes with perfluoroorganometallic reagents followed by treatment with hydrazines or amidines led to new polyfluorinated homo-C-nucleoside analogues, in a one-pot or two-step transformation, respectively.

A new approach to the synthesis of anomeric sulfur analogues of CMP-Neu5Ac containing alkane or arene linkage la-d is described. The procedure involves the high β-stereoselectivity in sialylation of the peracetylated sialic acid methyl ester 4 with mercaptoalkyl (aryl) trichloroacetate 5a-d, followed by selective deprotection of the trichloroacetyl group to the corresponding hydroxyalkyl and hydroxyaryl thioglycosides 2a-d. Subsequent O-phosphitylation of 2a-d with respective 3a or 3c, followed by oxidation and deprotection led to the isolation of the target compounds la-d in good yields.

Showdomycin (1) and its anomer (2) have been prepared in four steps from readily available trichloroacetimidate 9. The key step involves reaction of the last compound with the title pyrrole 3 so as to form a chromatographically separable mixture of the pyrrole C-glycosides 10 and 11. These pyrroles are desilylated then oxidized to the corresponding maleimides using PCC.

Chlorodifluoromethyl groups were introduced into the 2-position of the glycals 1, 5, 8, and 11 by dithionite-mediated addition of CF 2 ClBr. The reaction proceeded stereoselectively, i.e. the CF 2 Cl-group is always found trans to the neighbouring substituent at C-3 in the products. Because the primarily formed glycosyl bromides hydrolyse easily, the corresponding 2-chlorodifluoromethyl-2-deoxypyranoses 3, 6, 9, and 12 were isolated. Only 3,4,6-tri-O-acetyl-2-chlorodifluoromethyl-2-deoxy-D-glucopyranosyl bromide (2) was stable enough for chromatographic separation. The unprotected anomeric pyranoses 3, 6, 9, and 12 were acetylated by acetic anhydride/pyridine yielding the 1-O-acetyl derivatives 4, 7, 10, and 13. These compounds are suitable glycosyl donors, just as the anomeric phenyl thioglycosides 16 and 17 generated from 1,3,4-tri-O-acetyl-2-chlorodifluoromethyl-2-deoxy-D-arabinopyranside (7) and thiophenol (BF 3 -catalysis). Furthermore, the reactivity of glucosyl bromide 2, 6-deoxy-L-glucose derivative 13 and thioglycosides 16, 17 was investigated. On treatment of glucosyl bromide 2 with pyridine, the 2-chlorodifluoromethyl substituted glycal 14 is formed as the result of HBr elimination. Furthermore, the chlorodifluoromethyl group of compounds 14 and 16 was converted into a methoxycarbonyl group by refluxing in methanolic sodium methoxide (products 15 and 19, respectively). Finally, the thioglycosides 16 and 17 were subsequently deacetylated by CsF on alumina (yielding the dihydroxy derivatives 18 and 20) and acetalized with chloral/DCC (18 forming acetal 21 and carbonate 22) and acetone (20 forming acetal 23), respectively. X-ray analyses are given for the 1-O-acetate 4 and the thioglycosides 21 and 24.

Reaction of (2S,3R,5S,6S)-2-methoxy-3,5-dimethyl-tetrahydro-2H-pyran-6-carbaldehyde (a-8) with MeMgCl gave (6'S)-α-9 as a single isomer which was converted into (5S,6R)-epoxide (cis-12) by a sequence of reactions involving tosylation, ring-opening by the reaction with HS(CH 2 ) 3 SH, and treatment with NaOMe. When α-8 and its β-anomer (β-8) respectively reacted with MeTi(Oi-Pr) 3 and the resulting alcohols were subjected to similar transformation as above, (55,65)-epoxide (trans-12) was obtained irrespective of the anomeric configuration. The reaction of trans-12 with lithium alkynylaluminates 13a and 13b took place at the position 6 to afford the corresponding alkynes 14a and 14b.

A series of novel guanidinoglycosides was successfully synthesized. This was accomplished with the use of Mitsunobu conditions as a strategy to convert the glycopyranose anomeric hydroxy group to give the corresponding substituted masked guanidines in high yields. Subsequent deprotection and coupling with Fmoc protected β-amino acid, afforded a series of N,N'-substituted-methyl-isothioureas. Cleavage of Fmoc followed by concomitant cyclization was achieved with a catalytic amount of DBU to give the guanidinoglycosides.

The first Lewis acid mediated stereoselective removal of an anomeric chiral urea group or an electron deficient nitrogen substituent is described here. The ability to remove this urea group which had served as a chiral auxiliary, along with stereoselective hydroboration-oxidation of the endocyclic olefin renders the pyranyl cycloadduct from hetero [4+2] cycloadditions of chiral allenamides a useful chiral template. This represents a new approach to synthesis of complex pyranyl heterocycles or C-glycoside derivatives.

The title indolizidine, a ring-modified analog of the potent mannosidase inhibitor (-)-swainsonine, has been prepared by intramolecular nucleophilic addition of the sp 2 -type nitrogen atom of a preformed 1,3-oxazine-2-thione heterocycle to the masked aldehyde group in a D-mannose precursor; the stereochemistry of the generated aminoacetalic stereocenter is governed by the generalized anomeric effect, the pseudoanomeric hydroxyl group adopting an axial orientation that mimics that of α-D-mannopyranoside aglycons.

A wide variety of thioglycosides 1 are selectively hydrolyzed to the corresponding 1-hydroxy sugars 2 in good yields at 0-5 °C, by employing V 2 O 5 -H 2 O 2 catalyzed oxidation of ammonium bromide in CH 2 Cl 2 -H 2 O solvent system. The methodology is very mild, environmentally benign, efficient and highly chemoselective. No side reactions such as bromination either at the anomeric position or double bond or oxidation at the sulfur are encountered.

Glycosyl phosphates have emerged as useful glycosyl donors for stereoselective glycosidic bond formation in the synthe- sis of oligosaccharides. In this account, we describe some of our work in developing and further expanding this methodology, partic- ularly with the use of propane-1,3-diyl phosphate as the anomeric leaving group. We have studied the reactions of several glycosyl propane-1,3-diyl phosphates with or without C-2 participating groups with a range of glycosyl acceptors in the presence of trime- thylsilyl triflate in either stoichiometric or catalytic amount, and demonstrated their application in the synthesis of several disaccha- rides and also the synthesis of some trisaccharides.

Glycosylation of alcohols containing acid-sensitive groups, as tor example 1,2-5,6-di-O-isopropylidene-glucofuranose, Fmoc-threonine tert-butyl ester or famesol, is achieved using glycosyl trichloroacetimidates activated by gold(I) chloride (5―10 mol%). While glycosylation with 2-O-acyl protected glycosyl donors proceeds with 1,2-trans-selectivity, non-neighboring group active glycosyldonors give mixtures of anomeric glycosides or α-glycosides depending upon their structure and the reactivity of the glycosyl acceptor.

Efficient synthesis of clitocine has been accomplished via unprecedented 1,3-N (endo) to N (exo) migration as a key transformation. Incorporation of p-chlorobenzoyl (PCB) group as a protecting group led to the easy solidification of the intermediate of 7, thus making the isolation very facile and to the minimization of the epimerization of the anomeric center at the final deprotection stage.

A novel benzyl-type fluorous support (HfBn-OH) has been easily prepared, and the HfBn group was successfully introduced to the anomeric position of the carbohydrate, then removed in high yield after working as a support. The use of the HfBn group made it possible to synthesize an oligosaccharide with minimal column chromatography purification. It was found that each HfBn derivative as a synthetic intermediate is easily purified only by fluorous-organic solvent extraction.

Anomeric 1-(3-deoxy-D-erythro-2-hexulofuranosyl)thymines and 9-(3-deoxy-D-erythro-2-hexulofuranosyl)adenines were prepared by tin(IV) chloride catalyzed N-glycosylation of trimethylsilylated thymine and N 6 -benzoyladenine with methyl 3-deoxy-D-erythro-2-hexulofuranoside triacetate or tribenzoate, respectively. These O-glycosides used as starting materials were obtained by deoxygenation of 1,2:4,5-di-O-isopropylidene-β-D-fructopyranose and subsequent acid-catalyzed methanolysis of the resulting 3-deoxy derivative. The anomeric configuration of the nucleosides prepared was assigned by a combination of X-ray crystallography and 2D 1 H NMR spectroscopy. The conformation and hydrolytic stability of these new nucleoside analogous are discussed

Methyl 2,3-dideoxy-3-fluoro-5-0-(4-phenylbenzoyl)-β-D-erythro-pentofuranoside was condensed with trimethylsilylated 5-substituted uracils to give nucleosides using trimethylsilyl trifluoromethanesulfonate as catalyst. In the case of 5-nitrouracil an acyclic nucleoside believed to be an intermediate for the corresponding nucleoside was isolated. The 5-substituents were selected from neural network calculations on compounds with potential activity against HIV-1. All compounds from the condensation reactions were deacylated by treatment with sodium methoxide in methanol