Cyanosugars III : The reaction of trimethylsilyl cyanide with keto,epoxy and acetal derivatives of carbohydrates

Reaction of methyl 2-acetamido-4,6-$\text{O}$-benzylidene-2-deoxy-α-$\text{D}$-$\text{ribo}$-hexopyranosid-3-ulose with Me₃SiCN afforded methyl 2-acetamido-4,6-$\text{O}$-benzylidene-3-$\text{C}$-cyano-2-deoxy-3-$\text{O}$-trimethylsilyl-α-$\text{D}$-$\text{allo}$- Reaction of ethyl 4,6-di-$\text{O}$-acetyl-2,3-anhydro-α-$\text{D}$-mannopyranoside with Me₃SiCN gave the corresponding ethyl 4,6-di-$\text{O}$-acetyl-2-$\text{C}$-cyano-2-deoxy-α-$\text{D}$-glucopyranoside. Reaction of methyl 4,6-$\text{O}$-benzylidene-2,3-anhydro-α-$\text{D}$-allopyranoside or methyl 4,6-$\text{O}$-benzylidene-2,3-di-$\text{O}$-tosyl-α-$\text{D}$-glucopyranoside with Me₃SiCN at - 75° or - 50° gave the corresponding methyl 6-$\text{O}$-[(R)-cyano phenyl methyl]-α-$\text{D}$-glyco-pyranosides with high or total regio and stereoselectivity.     

Synthesis of novel chiral phosphines from α,α-trehalose

New disaccharide chiral phosphines, such as 4,6-O-benzylidene-2-(diphenylphosphino)-2-deoxy-α-d-altropyranosyl-(1,1)-4,6-O-benzylidene-2-(diphenylphosphino)-2-deoxy-α-d-altropyranoside 1 and 2-(diphenylphosphino)-2-deoxy-4,6-O-isopropylidene-α-d-altropyranosyl-(1,1)-2-(diphenylphosphino)-2-deoxy-4,6-O-isopropylidene-α-d-altropyranoside 9, were prepared from α,α-trehalose. We also succeeded in the synthesis of polyhydroxy chiral diphosphine 2-(diphenylphosphino)-2-deoxy-α-d-altropyranosyl-(1,1)-2-(diphenylphosphino)-2-deoxy-α-d-altropyranoside 5 by deprotection of isopropylidene groups.     

Synthesis of Methyl 2-Acetamido-4,6-di-O-acetyl-3-S-acetyl-2-deoxy-3-thio-α-D-mannopyranoside

Methyl-2-acetamido-4,6-di-O-acetyl-3-S-acetyl-2-deoxy-3-thio-α-D-mannopy-ranoside has been synthesized by conversion of methyl 2-amino-2-deoxy-4,6-O-benzylidene-α-D-altropyranoside into the corresponding 3-O-methanesulfony1-2-N-[(methylthio)thiocarbonyl]derivative followed by intramolecular displacement of the 3-O-methanesulfonyloxy group with the (methylthio)thiocarbamoyl group.     

Application of Phenyl 1-Selenoglycosides in the Synthesis of a Cell-Wall Tetrameric Fragment of Proteus Vulgaris Strain 5/43

Abstract

DAST-assisted rearrangement of 3-O-allyl-4-O-benzyl-α-l-rhamnopyranosyl azide followed by treatment of the generated fluorides with ethanethiol and BF₃·OEt₂ gave glycosyl donor ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside. Stereoselective glycosylation of methyl 4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside with ethyl 3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-1-thio-α/β-l-glucopyranoside, under the agency of NIS/TfOH afforded methyl 3-O-(3-O-allyl-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzyli-dene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Removal of the allyl function of the latter dimer, followed by condensation with properly protected 2-azido-2-deoxy-glucosyl donors, in the presence of suitable promoters, yielded selectively methyl 3-O-(3-O-[6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-α-D-glucopyranosyl]-2-azido-4-O-benzyl-2,6-dideoxy-α-l-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside. Deacetylation and subsequent glycosylation of the free HO-6 with phenyl 2,3,4,6-tetra-O-benzoyl-1-seleno-β-D-glucopyranoside in the presence of NIS/TfOH furnished a fully protected tetrasaccharide. Deprotection then gave methyl 3-O-(3-O-[6-O-{β-D-glucopyranosyl}-2-acetamido-2-deoxy-β-D-glucopyranosyl)-2-acetamido-2,6-dideoxy-α-L-glucopyranosyl)-2-acetamido-2-deoxy-β-D-glucopyranoside.     

Synthesis of the Immunodominant Trisaccharide Related to the Antigen From E. COLI O 126

The trisaccharide derivative methyl 2-O-[4,6-di-O-acetyl-3-O-(2,3,4,6-tetra-O-benzyl-α-D-gal-actopyranosyl)-2-deoxy-2-phthalimido-β-D-gluco-pyranosyl]-4,6-O-benzylidene-β-D-mannopyranoside (12) was obtained when 3-O-(2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl)-4,6-di-Oacetyl-2-deoxy-2-phtha-limido-β-D-glucopyranosyl trichloroacetimidate (8) was allowed to react with methyl 3-O-benzyl-4,6-O-benzylidene-β-D-mannopyranoside (11) in presence of trimethylsilyl triflate. Removal of protecting groups then gave the desired trisaccharide.     

Strukturelle Abwandlungen an partiell silylierten Kohlenhydraten mittels Triphenylphosphin/Azodicarbonsäure-diäthylester. 3. Mitteilung [1]

Structural Modification on Partially Silylated Carbohydrates by Means of Triphenylphosphine/Diethyl Azodicarboxylate Reaction of methyl 2, 6-bis-O-(t-butyldimethylsilyl)-β-D -glucopyranoside ( 1a ) with triphenylphosphine (TPP)/diethyl azodicarboxylate (DEAD) and Ph₃P · HBr or methyl iodide yields methyl 3-bromo-2, 6-bis-O-(t-butyldimethylsilyl)-3-deoxy-β-D -allopyranoside ( 3a ) and the corresponding 3-deoxy-3-iodo-alloside 3c (Scheme 1). By a similar way methyl 2, 6-bis-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 2a ) can be converted to the 4-bromo-4-deoxy-galactoside 4a and the 4-deoxy-4-iodo-galactoside 4b . In the absence of an external nucleophile the sugar derivatives 1a and 2a react with TPP/DEAD to form the 3,4-anhydro-α- or -β-D -galactosides 5 and 6a , respectively, while methyl 4, 6-bis-O-(t-butyldimethylsilyl)-β-D -glucopyranoside ( 1b ) yields methyl 2,3-anhydro-4, 6-bis-O-(t-butyldimethylsilyl)-β-D -allopyranoside ( 7a , s. Scheme 2). Even the monosilylated sugar methyl 6-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 2b ) can be transformed to methyl 2,3-anhydro-6-O-(t-butyldimethylsilyl)-β-D -allopyranoside ( 8 ; 56%) and 3,4-anhydro-α-D -alloside 9 (23%, s. Scheme 3). Reaction of 1c with TPP/DEAD/HN₃ leads to methyl 3-azido-6-O-(t-butyldimethylsilyl)-3-deoxy-β-D -allopyranoside ( 10 ). The epoxides 7 and 8 were converted with NaN₃/NH₄Cl to the 2-azido-2-deoxy-altrosides 11 and 13 , respectively, and the 3-azido-3-deoxy-glucosides 12 and 14 , respectively (Scheme 4 and 5). Reaction of 7 and 8 with TPP/DEAD/HN₃ or p-nitrobenzoic acid afforded methyl 2,3-anhydro-4-azido-6-O-(t-butyldimethylsilyl)-4-deoxy-α- and -β-D -gulopyranoside ( 15 and 17 ), respectively, or methyl 2,3-anhydro-6-O-(t-butyldimethylsilyl)-4-O-(p-nitrobenzoyl)-α- and -β-D -gulopyranoside ( 16 and 18 ), respectively, without any opening of the oxirane ring (s. Scheme 6). - The 2-acetamido-2-deoxy-glucosides 19a and 20a react with TPP/DEAD alone to form the corresponding methyl 2-acetamido-3,4-anhydro-6-O-(t-butyldimethylsilyl)-2-deoxy-galactopyranosides ( 21 and 22 ) in a yield of 80 and 85%, respectively (Scheme 7). With TPP/DEAD/HN₃ 20a is transformed to methyl 2-acetamido-3-azido-6-O-(t-butyldimethylsilyl)-2,3-didesoxy-β-D -allopyranoside ( 25 , Scheme 8). By this way methyl 2-acetamido-3,6-bis-O-(t-butyldimethylsilyl)-α-D -glucopyranoside ( 19b ) yields methyl 2-acetamido-4-azido-3,6-bis-O-(t-butyldimethylsilyl)-2,4-dideoxy-α-D -galactopyranoside ( 23 ; 16%) and the isomerized product methyl 2-acetamido-4,6-bis-O-(t-butyldimethylsilyl)-2-deoxy-α-D -glucopyranoside ( 19d ; 45%). Under the same conditions the disilylated methyl 2-acetamido-2-deoxy-glucoside 20b leads to methyl 2-acetamido-4-azido-3,6-bis-O-(t-butyldimethylsilyl)-2,4-dideoxy-β-D -galactopyranoside ( 24 ). - All Structures were assigned by ¹H-NMR. analysis of the corresponding acetates.     

The Synthesis of Four Dideoxygenated Analogues of β-Maltosyl-(1→4)-Trehalose

Abstract

Four derivatives of β-maltosyl-(1→4)-trehalose were prepared, each with two deoxy functions in one of the constitutive disaccharide building blocks. 2,3-Di-O-acetyl-4,6-dideoxy-4,6-diiodo-α-D-galactopyranosyl- (1→4) ?1,2,3,6-tetra-O-acetyl-D-glucopyranose (3) was employed as a precursor for the 4?,6?-dideoxygenated tetrasaccharide 9: coupling of 3 with 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3,6-tri-O-benzylidene-α-D-glucopyranoside (4) furnished the tetrasaccharide 5 which was deiodinated and deprotected to yield the target tetrasaccharide 9. Secondly, the dideoxygenated maltose derivative 3-deoxy-4,6-O-isopropylidene-2-O-pivaloyl-β-D-glucopyranosyl- (1→4) ?1,6-anhydro-3-deoxy-2-O-pivaloyl-β-D-glucopyranose (10) was ring-opened to the anomeric acetate 11. A [2+2] block synthesis with 4 in TMS triflate mediated glycosylation gave a tetrasaccharide which was deprotected to the 3″,3?-dideoxygenated analogue of β-maltosyl-(1→4)-trehalose. For the third tetrasaccharide, 2,3,2″,3′-tetra-O-benzyl-α,α-trehalose was iodinated at the primary positions and deiodinated in the presence of palladium-on-carbon, then this acceptor was selectively glycosylated with hepta-O-acetyl-maltosyl bromide (20). Removal of protective groups furnished the maltosyl trehalose tetrasaccharide deoxygenated at positions C-6 and C-6′. to prepare a 3,3′-dideoxygenated trehalose, the free hydroxyl groups of 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranosyl 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranoside (25) were reduced by Barton-McCombie deoxygenation. One of the benzylidene groups was opened reductively with sodium cyanoborohydride. The resulting free hydroxyl group at the 4′-position was glycosylated in a Koenigs-Knorr reaction with 20 to yield the 3,3′-dideoxygenated tetrasaccharide 32, the fourth target oligosaccharide, after deprotection.     

Observations on the electron impact induced fragmentation of methyl and phenyl 4,6-O-Benzylideneglucopyranosides

The structure of some rearrangement ions in the electron impact induced fragmentation of methyl 4,6-O-benzylidene-2,3-di-O-methyl-α-D -glucopyranoside and phenyl 4,6-O-benzylidene-2,3-di-O-methyl-β-D -glucopyranoside have been investigated using high resolution, deuterium labelling and linked scan (B,E) techniques. Shifts of methoxyl groups from C-2 and C-3 to C-1 have been confirmed.     

Selectively Deoxygenated Derivatives of β-Maltosyl-(1→4)-Trehalose as Biological Probes

ABSTRACT

The four derivatives of β-maltosyl-(1→4)-trehalose have been synthesized, which are monodeoxygenated at the site of one of the primary hydroxyl groups. The tetrasaccharides were constructed in [2+2] block syntheses. Thus, 6′″-deoxy-β-maltosyl-(1→4)-trehalose was prepared by selective iodination of allyl 2,3,6,2′,3′-penta-O-acetyl-β-maltoside (3) followed by catalytic hydrogenolysis and coupling with 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranosyl 2′,3′,6′-tri-O-benzyl-α-D-glucopyranoside (9), and 6″-deoxy-β-maltosyl-(1→4)-trehalose by selective iodination of allyl 4′,6′-O-isopropylidene-β-maltoside (14), coupling with 9, and one-step hydrogenolysis at the tetrasaccharide level. For the synthesis of 6′-deoxy-β-maltosyl-(1→4)-trehalose, the diol 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranosyl 2′,3′-di-O-benzyl-α-D-glucopyranoside (22) was selectively iodinated and glycosylated with acetobromomaltose followed by catalytic hydrogenolysis. The 6-deoxy-β-maltosyl-(1→4)-trehalose was obtained upon selective iodination of a tetrasaccharide diol.     

Preparation of 2-Azido-4-O-benzoyl-2,6-dideoxy-3-O-methyl-β-D-allopyranose and Its Disaccharide Derivative

Abstract

2-Azido-4-O-benzoyl-2,6-dideoxy-3-O-methyl-D-allopyranose, needed as one of the building blocks for construction of a novel cyclodextrin-like compound, was prepared in the form of crystalline β-anomer 6 from methyl 2-azido-4,6-O-benzylidene-2-deoxy-α-D-allopyranoside 1. As a model of α-glycosidation necessary for formation of a cyclic structure, 6 was converted into the corresponding β-glycosyl trichloroacetimidate and coupled with methyl 6-O-benzyl-2,3-di-O-methyl-α-D-glucopyranoside 8, giving α(1→4)-linked disaccharide derivative 9.     

2-Deoxy-2-C-(2,3-dideoxy-α-d-erythro-hexopyranosyl)-β-d-glucopyranoses: Reinvestigation of Synthesis,Use in Glycosylation,and Conformational Analyses by NMR

Abstract

Conformational investigations using 1D TOCSY and ROESY ¹H NMR experiments on 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hexopyranosyl)-2-deoxy-β-D-glucopyranose (8) and related disaccharides showed that for steric reasons the C-linked hexopyranosyl ring occurs in the usually unfavoured ¹C₄ conformation and reconfirmed the structure of 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)-2-deoxy-β-D-glucopyranose (5). Glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (13) with acetate 8 using trimethylsilyl triflate as a catalyst afforded the α-D-linked tetrasaccharide 14. A remarkable side product in this reaction was the unsaturated tetrasaccharide 2,3,6-tri-O-benzyl-4-O-[4,6-di-O-acetyl-2,3-dideoxy-2-C-(4,6-di-O-acetyl-2,3-dideoxy-β-D-erythro-hexopyranosyl)-α-D-erythro-hex-2-enopyranosyl]-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (16) where in the C-linked hexopyranosyl ring an isomerization to the β-anomer had taken place to allow for the favoured ⁴C₁ conformation. The tetrasaccharide 14 was deacetylated and hydrogenolyzed to form the fully deprotected tetrasaccharide 18. The ¹ C ₄ conformation of the C-glycosidic pyranose of this tetrasaccharide was maintained as shown by an in depth NMR analysis of its peracetate 19.     

Synthesis of Four Spacer-Containing Trisaccharides with the 4-0-(β-L-Rhamnopyranosyl)-D-glucopyranose Unit in Common,Representing Fragments of Capsular Polysaccharides from Streptococcus Pneumoniae Types 2, 7F, 22F,and 23F

Abstract

The synthesis is reported of 3-aminopropyl 3-O-[4-O(β-L-rhamnopyranosyl)-β-D-glucopyranosyl]-α-L-rhamnopyranoside (34), 3-aminopropyl 2-acetamido-3-O-[4-0-(β-L-rhamnopyranosyl)-β-D-glucopyranosyl]-2-deoxy-β-D-galactopyranoside (37), 3-aminopropyl 3-O-[4-O-(β-L-rhamnopyranosyl)-α-D-glucopyranosyl]-α-D-galactofuranoside (41), and 3-aminopropyl 4-O-[4-O-(β-L-rhamnopyranosyl)-β-D-glucopyranosyl]-β-D-galactopyranoside (45). These are spacer-containing fragments of the capsular polysaccharides of Streptococcus pneumoniae type 2, 7F, 22F, and 23F, respectively, which are constituents of Pneumovax^© 23. 2,3,4-Tri-O-benzyl-α-L-rhamnopyranosyl bromide was coupled to l,6-anhydro-2,3-di-(O-benzyl-β-D-glucopyranose (3). Opening of the anhydro ring, removal of AcO-1, and imidation of l,6-anhydro-2,3-di- O-benzyl-4-O-(2,3,4-tri-O-benzyl-β-L-rhamnopyranosyl)-β-D-glucopyranose (4β) afforded 6-O-acetyl-2,3-di-O-ben-zyl-4-O-(2,3,4-tri- O-benzyl-β-L-rhamnopyranosyl)-αβ-D-glucopyranosyl trichloroacet-imidate (7αβ). Condensation of 7αβ with 3-N-benzyloxycarbonylaminopropyl 2-O-ben-zyl-5,6-O-isopropylidene-α-D-galactofuranoside (26), followed by deprotection gave 41 Opening of the anhydro ring of 4 p followed by debenzylation, acerylauon, removal of AcO-1, and imidation yielded 2,3,6-tri-(9-aceryl-4-O-(2,3,4-tri-0-acetyl-P-L-rharnnopyran-.-osyl)-α-D-glucopyranosyl trichloroacetimidate (11). Condensation of 11 with 3-N-bcn-zyloxycarbonylaminopropyl 2,4-di-O-benzyl-α-L-rhamnopyranoside (18), with 3-N-bcn-zyloxycarbonylaminopropyl 2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-galactopyran-oside (21), or with 3-N -benzyloxycarbonylaminopropyl 2-O-acetyl-3-O-allyl-6-O-benzyl-β-D-galactopyranoside (31), followed by deprotection afforded 34, 37, and 45, respectively.     

Synthesis of the repeating trisaccharide unit of the cell wall lipopolysaccharide of Escherichia coli type 8

NIS/TfOH mediated glycosidation of methyl 3,4,6-tri-O-benzyl-α-d-mannopyranoside with phenyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-d-mannopyranoside furnished the corresponding disaccharide derivative in excellent yield and α-selectivity. Zémplen deacetylation of the same followed by reaction with BSP/Tf₂O-preactivated phenyl 4,6-O-benzylidene-2,3-di-O-benzyl-1-thio-α-d-mannopyranoside generated methyl 4,6-O-benzylidene-2,3-di-O-benzyl-β-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranoside in very good yield and excellent β-selectivity. Pd/C catalyzed hydrogenation of the latter finally afforded the repeating trisaccharide of Escherichia coli 8 O-antigen as its methyl glycoside.     

Mono-Triflation of Carbohydrate Diols and Triols

ABSTRACT

For five carbohydrate substrates [methyl 4,6-O-(phenylmethylene)-1-thio-α-D-glucopyranoside 1a, 1-cyano-1-deoxy-4,6-O-(phenylmethylene)-α-D-galactopyranose 2a, methyl α-D-xylopyranoside 3a, methyl β-D-arabinopyranoside 4a, and methyl 5-O-(tert-butyldiphenylsilyl)-α-D-ribofuranoside 5a], selective mono-triflation was achieved where the reacting hydroxyl is cis and vicinal to a heteroatom.     

Talopyranose Derivatives Suitable for the Planned Synthesis of Teichoic Acids Containing Di-Glycosylated Ribitol Units

ABSTRACT

Easily accessible 1,6-anhydro-2,3-O-(S)-benzylidene-β-D-mannopyranose was converted in four steps to 1,6-anhydro-3,4-di-O-benzyl-β-D-talopyranose. Glycosylation of the latter with ethyl 2,3,4-tri-O-acetyl-1-thio-α-L-rhamnopyranoside gave, after further processing, 1-O-allyl-3,4-di-O-benzyl-2-O-(2,3,4-tri-O-benzyl-α-L-rhamnopyranosyl)-L-ribitol.     

Synthesis Of Ligands Related To The O-Specific Antigen Of Shigella Dysenteriae Type 1.

Abstract

Stereoselective α-D-galactosylation at the position 3 of 4,6-O-substituted derivatives of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside is described. Glycosyl chlorides derived from 3,4,6-tri-O-acetyl-2-O-benzyl- and 2-O-(4-methoxybenzyl)-D-galactopyranose have been used as glycosyl donors. Methyl 2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (27) and methyl 2-acetamido-4,6-di-O-benzyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (31) have been prepared.     

arabinonucleosides

The α-D-arabinonucleosides of cytosine ( 6 ) and 5-fluorouracil ( 9 ) were prepared from the 2,3,-5-tri-O-benzoyl-D-arabinofuranosyl halides, in keeping with the trans rule. The 2′-O-methyl-)3-D-arabinonucleosides of 5-fluorouraeil (β- 14 ) and adenine (β- 21a ) were prepared from 3,5-di-O-(4-ehlorobenzoyl)-2-O-methyl-α-D-arabinofuranosyl chloride, although in both cases a lesser amount of the α-anomer was also found. Reaction of 3,5-di-O-(4-chlorobenzoyl)-2-deoxy-2-(methylthio)-α-D-arabinofuranosyl chloride, prepared in four steps from methyl 2,3-anhydro-α-D-ribofurano-side ( 15 ), with N-benzoyladenine gave slightly more of the β- than the α-arabinonucleoside 20b . The β-anomer was converted to 9-[2-deoxy-2-(methylthio)-β-D-arabinofuranosyl]adenine. Only 1-α-D-arabinofuranosylcytosine ( 6 ) proved to be cytotoxic.     

Syntheses of Model Oligosaccharides of Biological Significance. VI. Glycosylation at C-3 of Galactose: A Synthesis of Trideuterio-Methyl 3-O-(-Acetamido-2-Deoxy-β-D-Glucopyranosyl)-β-D-Galactopyranoside

The title disaccharide was prepared by glycosylation of either methyl trideuteriomethyl 2-O-benzoyl-4,6-benzylidene-β-D-galactopyranoside or trideuteriomethyl-4,6-O-benzylidene-β-D-galactopyranoside with 3,4,6-tri-Oi-acetyl 2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide using silver zeolite 13X or silver triflate as promoters.     

Synthesis of Methyl α-d-Allopyranoside and Methyl α-d-Ribo-hexopyranoside: A Convenient Chemoenzymatic Approach

Abstract

An efficient chemoenzymatic synthesis of methyl α-d-allopyranoside and methyl 3-deoxy-α-d-ribo-hexopyranoside starting from methyl 4,6-O-benzylidene-α-d-glucopyranoside is described.     

Towards cyclic,conformationally constrained,fluorine-containing β-amino acid derivatives from d-glucose

Novel, potentially bioactive, fluorinated branched-chain monosaccharides were obtained by reaction of diethylaminosulphur trifluoride (DAST) with a series of methyl 3-C-cyano-3-ethoxycarbonyl-β-d-glucopyranoside derivatives, including the 4,6-O-benzylidene derivative and their 3-C-(N-protected aminomethyl) reduction products, as well as the phenyl 3-C-cyano-3-ethoxycarbonyl-1-thio-α-d-(and β-d-)glucopyranosides. The absolute configuration at C(3) was unambiguously assigned for all compounds on the basis of X-ray crystallographic analysis of methyl 4,6-O-benzylidene-3-C-cyano-3-deoxy-3-ethoxycarbonyl-β-d-glucopyranoside, corroborating the previous tentative assignment by other authors for the 4,6-unprotected compound. The course of the fluorination depended on the reaction temperature and the substitution pattern of the substrate. Thus, for methyl 3-C-cyano-3-ethoxycarbonyl-β-d-glucopyranoside, fluorination occurred exclusively at C(6), but for the phenylthio analogue, a 2-deoxy-2-phenylthio-α-d-manno-configured glycosyl fluoride and its 6-fluoro derivative were obtained, resulting from the expected rearrangement reaction, whilst starting from the phenylthio α anomer, only the unrearranged 6-fluoro compound was formed. Rearrangement was also observed in the fluorination of methyl 4,6-O-benzylidene-3-C-(N-protected aminomethyl)-β-d-glucopyranoside, which led to the 2-O-methyl-α-d-mannopyranosyl fluoride derivative as the sole product. This methodology may constitute a simple route to enantiopure conformationally constrained cyclic fluorinated β-amino acids having the α carbon atom shared with a pyranose ring, although only moderate yields were achieved, particularly in the fluorination step.