摘要:

The similarities in bond length and polarization between C-F and C-OH, as well as the altered hydrogen-bonding properties present in carbohydrates bearing a fluorine atom in place of an hydroxyl group can be exploited in place of an hydroxyl group can be exploited in biochemical investigations (enzyme-carbohydrate interactions, Lectin-carbohydrate affinities, antiobody-carbohydrate binding, etc.).1–5In addition, the different chemistries exhibited by the flourinated carbohydrates have made them important reagents in both metabolic studies and disease diagnosis such as the use of 2-deoxy-2-[18f]-D-fluoroglucose in positron emission tomography. 6,7 Becasue of their widespread utlity, the synthesis of fluorinated carbohydrates is of importance. However, the Introduction of fluorine into a carbohydrate moiety can be an arduous task because of (1) the protection and deprotection steps required to set up the desired hydroxyl group for the introduction of fluoride, (2) the low nucleophilicity fo fluoride ion, and (3) fluoride ion catalyzed elimination reactions. 8,9 The search for Milder and more selective methods for the introduction of fluorine into Carbohydrates has continued at a rapid pace and it is appropriate to review som of the recent results.

ISSN:0732-8303    

DOI:10.1080/07328308508082671

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Electrophilicsynadditions of fluorine and acetylhypofluorite across double bonds in 3,4,6-tri-0-acetyl-D-glucal (1a) and D-glucal (1b) followed by acid hydrolysis gave mixtures of 2-deoxy-2-fluoro-D-glucose (8) and 2-deoxy-2-fluoro-D-mannose (9). These addition reactions were conducted in various solvents with a view to investigating the reaction mechanism based on the product distribution analysis by19F NMR. Tight ion pair intermediates (4and5) have been invoked to explain the stereospecific characteristics of the addition of fluorine or acetylhypofluorite to glycals. The relative stabilities of these intermediates control the product distributions and are governed by a) the anomeric effect (axial vs equatorial preference of C(1) electronegative substituents in pyranose rings), b) dipole-dipole interactions of the lone pairs of electrons on the ring oxygen and the electronegative substituents on C(2), and c) the gauche relationship that exists between the C(2) fluorine and polar groups in the molecule. The overall contribution of these three factors largely depends upon the polarity of the solvent. A rationale for the19F NMR chemical shifts as well as the anomeric distributions of the α and β anomers of 2-FDG (8) and 2-FDM (9) has been proposed.

ISSN:0732-8303    

DOI:10.1080/07328308508082672

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Starting from 1,2-O-isopropylidene-α-D-gluco- and -β-L-ido-furanurono-6,3-lactone, 5-deoxy-5-fluoro-α/β-D-gluco- and -L-idofuranose, respectively, were prepared by the following sequence of reactions: trifluoromethanesulfonylation, nucleophilic substitution with inversion of configuration, lactone reduction and deprotection. On the basis of H-H-, H-C-, H-F-, and C-F-couplings, the stereochemistry of the products is discussed.

ISSN:0732-8303    

DOI:10.1080/07328308508082673

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Reaction of 1,2-0-alkylidenehexofuranurono-6,3-lactones with diethylaminosulfur trifluoride (DAST) led to 1,2-0-alkylidene-5-deoxy-5-fluorohexofuranurono-6,3-lactones (13–30%) together with 1,2-0-alkylidene-3,6-anhydro-6,6-difluorohexofuranoses (45–58%). Evidence was found for participation of the hydroxyl group at C-5 in the formation of the difluorides. Trifluoro compounds could not be prepared by reaction with DAST but were formed from the difluorides by triflate formation and displacement using tetra-n-butylammonium fluoride.

ISSN:0732-8303    

DOI:10.1080/07328308508082674

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

1-Propenyl 4,6-Q-benzylidine-β-D-mannopyranoside-2,3-cyclic sulfate was prepared from methyl α-D-mannopyranoside. This compound reacts cleanly with tetramethylammonium fluoride, followed by add hydrolysis (2N HC1), to give 2-deoxy-2-fluoro-D-glucose. The reaction is suitable for use with the short lived radionuclide fluorlne-18 (t1/2,=110 minutes).

ISSN:0732-8303    

DOI:10.1080/07328308508082675

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A simple method for the preparation ofO-tri-fluoromethyl carbohydrate derivatives is reported. Carbohydrate derivatives bearing excellent leaving groups can react with tris(dimethylamino)sulfonium trifluoromethoxide (TAS+CF3-O-) to afford trifluoro-methoxy-substituted compounds along with varying amounts of the corresponding deoxyfluoro products. Primary and secondary triflates afford the corresponding trifluoromethyl ethers. Displacement at a secondary center occurs with complete inversion of configuration. Glucosyl bromides react to form mixtures of trifluoromethyl glucosides and glucosyl fluorides.

ISSN:0732-8303    

DOI:10.1080/07328308508082676

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A treatment of 2,3,5-tri-O-benzyl-B-D-ribofuranosyl fluoride (1) with cyanotrimethylsilane in the presence of boron trifluoride diethyl etherate gave 2,3,5-tri-O-benzyl-α- (2α) and -β-D-ribofuranosyl (2β) cyanide in 46.2% and 46.6% yields, respectively. Confirmation of the corresponding isocyano isomer (3) formation and its conversion into2under boron trifluoride catalysis at -78°C made it possible to deduce that both2αand2βwere produced by way of3which was formed preponderantly in the initial stage of the reaction. On the other hand, the reaction of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (4) with cyanotrimethylsilane in diethyl ether by the use of boron trifluoride diethyl etherate (0.05 mol. equiv.) gave 2,3,4,6-tetra-O-benzyl-α -D-glucopyranosyl cyanide (5α), 2,3,4,6-tetra-O-benzyl-α- (6α), and -β-D-glucopyranosyl isocyanide (6β) as a 30:61:9 mixture (94% yield) but that in dichloromethane by the use of the catalyst (1.0 mol. equiv.) gave5α(85% yield) as a sole product.

ISSN:0732-8303    

DOI:10.1080/07328308508082677

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

2′,3′-Dideoxy-2′-fluorokanamycin A (23) was prepared by condensation of 6-azido-4-0-benzoyl-2,3,6-trideoxy-2-fluoro-α-D-ribo-hexopyranosyl bromide (13) and a protected disaccharide (19). Methyl 4,6-0-benzylidene-3-deoxy-β-D-arabino-hexopyranoside (5) prepared from methyl 4,6-0-benzylidene-3-chloro-3-deoxy-β-D-allo-hexopyranoside (1) by oxidation with pyridinium chlorochromate followed by reduction with Na2S2O4was fluorinated with the DAST reagent to give methyl 4,6-O-benzylidene-2,3-dideoxy-2-fluoro-β-D-ribo-hexopyranoside (7). Successive treatment of7with NBS, NaN3and SOBr2gave13. The structure of the final product (23) was determined by the1H and19F and shift-correlated 2D NMR spectra.

ISSN:0732-8303    

DOI:10.1080/07328308508082678

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Bromoacetylation of methyl 2,4-di-O-benzoyl-3-deoxy-3-fluoro-β-D-galactopyranoside, followed by the cleavage of the methoxy group from the resulting 6-O-bromoacetyl derivative 2 with 1,1-dichloromethyl methyl ether gave 2,4-di-0-benzoyl-6-0-bromoacetyl-3-deoxy-3-fluoro-α-D-galactopyranosyl chloride (3). Reaction of 3 with methyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside promoted by silver trifluoromethanesulfonate afforded methyl0-(2,4-di-O-benzoyl-6-O-bromoacetyl-3-deoxy-3-fluoro-β-D-galacto-pyranosyl)-(1→6)-2,3,4-tri-O-benzoyl-β-D-galactopyranoside (5).O-Debromoacetylation of5with thiourea gave the disaccharide nucleophile6which was condensed with 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl bromide to afford the expected β-(trans)-linked trisaccharide derivative7. Debenzoylation of7gave the methyl β-glycoside 8 of the (1→6)-linked D-galactotriose having the HO-3 of the internal residue replaced by a fluorine atom. Compound 8 was used to further delineate the subsites in the combining area of the monoclonal anti-(1→6)-β-D-galactan-specific immunoglobulin IgA J539.

ISSN:0732-8303    

DOI:10.1080/07328308508082679

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The reaction of methyl or benzyl 3-azido-5-0-benzoyl-3,6-di-deoxy-α-L-talofuranoside with (diethylamino)sulfur trifluoride (DAST) in toluene at 60°C resulted in the formation of 3-azido-5-0-benzoyl-3,6-dideoxy-2-0-methyl (or 2-0-benzyl)-3β-L-galactofuranosyl fluoride in good yield. In this reaction the alkoxyl group at C-1 migrated to the C-2 position and a fluorine atom entered into the C-1 position. The furanosyl fluoride was converted,viareduction of the azido group followed byN-trifluoroacetylation, acetolysis, andO-deacetylation, into 3,6-dideoxy-2-0-methyl-3-trifluoroacet-amido-L-galactopyranose (2-methoxy-Daunosamine derivative).

ISSN:0732-8303    

DOI:10.1080/07328308508082680

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor