Synthesis of benzyl and methyl 3-benzamido-2,3,6-trideoxy-2-fluoro-β-l-galactopyranoside: Protected C-2 fluoro analogues of daunosamine

The reaction of benzyl 2-benzamido-4,6-O-benzylidene-2-deoxy-3-O-tosyl-α-d-glucopyranoside or benzyl 4,6-O-benzylidene-2,3-benzoylepimino-2,3-dideoxy-α-d-allopyranoside with anhydrous tetrabutylammonium fluoride in hexamethylphosphoric triamide gave ∼40% of benzyl 3-benzamido-4,6-O-benzylidene-2,3-dideoxy-2-fluoro-α-d-altropyranoside (6a). Transformation of 6a into benzyl 3-benzamido-2,3,6-trideoxy-2-fluoro-α-d-arabino-hex-5-enopyranoside (13a) was carried out by well-established methodology. Hydrogenation of the double bond in 13a furnished the title compound in good yield. Methyl 3-benzamido-2,3,6-trideoxy-2-fluoro-β-l-galactopyranoside was also prepared in nine steps from 2-amino-2-deoxy-d-glucose.     

The synthesis and degradation of benzyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside and -mannopyranoside

The use of carbohydrates for establishing, by synthesis, the absolute configuration of branched aliphatic alcohols is demonstrated by the synthesis and degradation of carbohydrate derivatives that contain two branch points. Benzyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside (23) and -mannopyranoside (24) were formed from benzyl 2,3-anhydro-4,6-O-benzylidene-α-d-mannopyranoside (17) by a reaction sequence that involved ring-opening with ethylmagnesium chloride, oxidation, epimerisation, methylenation, and hydroboronation. The gluco isomer 23 was converted into (+)-(R)-2,3-bisacetoxymethylpentyl acetate (1) by sequential hydrogenolysis, borohydride reduction, periodate oxidation, borohydride reduction, and acetylation. The synthesis of 1 provides confirmatory evidence for the absolute configuration of the alkaloid pilocarpine (2). Unidentified products, and not the expected free-sugars, were obtained by acidic hydrolysis of methyl 4,6-O-benzylidene-2,3-dideoxy-3-C-ethyl-2-C-hydroxymethyl-α-d-glucopyranoside (8) and -mannopyranoside (9). Convenient syntheses of benzyl α-d-glucopyranoside derivatives are described.     

Nucleophilic displacement reactions in carbohydrates : Part XX. Displacements on alkyl α-l-talopyranoside 4-sulphonate derivatives

The azide displacement reaction on methyl 6-deoxy-4-O-methanesulphonyl-2,3-di-O-methyl-α-l-talopyranoside (6) in N,N-dimethylformamide yielded methyl 4,6-dideoxy-2,3-di-O-methyl-α-l-threo-hex-3-enopyranoside (7, ca. 50%), methyl 4,6-dideoxy-2,3-di-O-methyl-β-d-erythro-hex-4-enopyranoside (8, ca. 10%), and methyl 4-azido-4,6-dideoxy-2,3-di-O-methyl-α-l-mannopyranoside (9, ca. 40%). The corresponding azide 14 (20%) and the unsaturated sugars 12 (68%) and 13 (12%) were obtained from a comparable reaction on benzyl 6-deoxy-4-O-methanesulphonyl-2,3-di-O-methyl-α-l-talopyranoside (11).     

Total synthesis of the mollu-series glycosyl ceramides alpha-D-Manp-(1----3)-beta-D-Manp-(1----4)-beta-D-Glcp-(1----1)-Cer and alpha-D-Manp-(1----3)-[beta-D-Xylp-(1----2)]-beta-D-Manp-(1----4)-beta- D-Glcp-(1----1)-Cer

The mollu-series glycosphingolipids, O-alpha-D-mannopyranosyl-(1----3)-O-beta-D-mannopyranosyl-(1----4)-O-bet a-D-glucopyranosyl-(1----1)-2-N-tetracosanoyl-(4E)-sphingeni ne and O-alpha-D-mannopyranosyl-(1----3)-O-[beta-D-xylopyranosyl-(1----2])-O- beta-D-mannopyranosyl-(1----4)-O-beta-D-glucopyranosyl-(1----1)-2-N- tetracosanoyl-(4E)-sphingenine, were synthesized for the first time by using 2,3,4-tri-O-acetyl-D-xylopyranosyl trichloroacetimidate, methyl 2,3,4,6-tetra-O-acetyl-1-thio-alpha-D-mannopyranoside, benzyl O-(4,6-di-O-benzyl-beta-D-mannopyranosyl)-(1----4)-2,3,6-tri-O-benzyl-be ta-D- glucopyranoside 9, and (2S,3R,4E)-2-azido-3-O-(tert-butyldiphenylsilyl)-4-octade cene-1,3-diol 6 as the key intermediates. The hexa-O-benzyl disaccharide 9 was prepared by coupling two monosaccharide synthons, namely, 2,3-di-O-allyl-4,6-di-O-benzyl-alpha-D-mannopyranosyl bromide and benzyl 2,3,6-tri-O-benzyl-beta-D-glucopyranoside. It was demonstrated that azide 6 was highly efficient as a synthon for the ceramide part in the coupling with both glycotriaosyl and glycotetraosyl donors, particularly in the presence of trimethylsilyl triflate.     

Chemoenzymatic synthesis of the 3-sulfated Lewisa pentasaccharide

The sulfated pentasaccharide benzyl O-(3-O-sulfo-beta-D-galactopyranosyl)-(1-->3)-O-[(alpha-L-fucopyranosyl)-(1-->4)]-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1-->3)-O-(beta-D-galactopyranosyl)-(1-->4)-O-beta-D-glucopyranoside sodium salt was synthesized using a chemo-enzymatic approach. Lacto-N-tetraose, obtained from two disaccharides [4-methoxybenzyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->3)-4,6-O-benzylidene-2-deoxy-2-phtalimido-beta-D-glucopyranoside and benzyl 2,6-di-O-acetyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-acetyl-beta-D-glucopyranoside], was regioselectively sulfated at the 3 OH position of the terminal galactose using the stannylene procedure. The fucosylation of the sulfated tetrasaccharide was performed using soluble or immobilized fucosyltransferase FucT-III to give the title compound.     

Acetylenes and dichloroanisoles from Psathyrella scobinacea

The Et2O extract from Psathyrella scobinacea culture fluids contained three new acetylenic alcohols: deca-5,7,9-triynol, (-)hepta-4,6-diyne-2,3-diol, and (-)hept-cis 4-en-6-yne-2,3-diol; two known dichloroanisoles: 3,5-dichloro-4-methoxybenzaldehyde and 3,5-dichloro-4-methoxybenzyl alcohol; and three known acetylenic acids: octa-2,4,6-triynoic acid, dec-trans-2-ene-4,6,8-triynoic acid and its cis-isomer.     

The synthesis of 2-acetamido-2-deoxy-6-O-β-d-mannopyranosyl-d-glucose

4,6-Di-O-acetyl-2,3-O-carbonyl-α-d-mannopyranosyl bromide was condensed with benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-α-d-glucopyranoside in the presence of silver carbonate to give crystalline benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-(4,6-di-O-acetyl-2,3-O-carbonyl-β-d-mannopyranosyl)-α-d-glucopyranoside in 32% yield. Removal of the protective O-acetyl and cyclic carbonate groups gave the crystalline benzyl α-glycoside of the disaccharide, which was catalytically hydrogenolyzed to yield the crystalline, title compound. Proof of the anomeric configuration of the interglycosidic linkage was obtained by comparison of the physical, spectral, and chromatographic properties of the disaccharide and its derivatives with those of the previously prepared α-d-linked analog.     

Modification of methyl O-propargyl-D-glucosides: model studies for the synthesis of alkynyl based functional polysaccharides

Methyl 4,6-O-benzylidene-2,3-di-O-propargyl-alpha-D-glucoside (2) has been prepared and its structure determined, including its X-ray structural analysis. For comparison the structure of the corresponding allyl derivative has also been determined by X-ray crystallography. Glucoside 2 is a versatile starting material for numerous novel derivatives such as diols, a diester, a diacid, and a dialdehyde. Subjecting 2 to a Mannich reaction leads to a (bis)amine in excellent yields. The click reaction between 2 and benzyl azide furnishes a (bis)triazole as the main product. Deprotection of 2 furnishes a (bis)propargyl ether, which can be converted by the methodology developed for 2 to the corresponding (bis)acetylenes; click reaction with benzyl azide converts 2 into a (bis)triazole.     

Preparation of 2,3-seco-5 alpha-cholestane-2,3-diol and 4 alpha-methyl-2,3-seco-5 alpha-cholestane-2,3-diol and its reactions with o-nitrophenyl selenocyanate

The reaction of 2,3-seco-5 alpha-cholestane-2,3-diol and 4 alpha-methyl-2,3-seco-5 alpha-cholestane-2,3-diol with o-nitrophenyl selenocyanate was studied. The diols were synthesized from cholesterol.     

Complexes of sodium vanadate(V) with methyl alpha-D-mannopyranoside,methyl alpha- and beta-D-galactopyranoside,and selected O-methyl derivatives: a 51V and 13C NMR study

The hydroxyl group stereochemistry of complexation of sodium vanadate(V) with Me alpha-Manp, Me alpha- and beta-Galp and selected O-methyl derivatives in D(2)O was determined by 51V, 1D and 2D 13C NMR spectroscopy at pD 7.8. The 51V approach served to show the extent of complexation and the minimum number of esters formed. That of Me alpha-Manp gave rise mainly to a 51V signal at delta -515, identical with that of its 4,6-di-O-methyl derivative, which had only a 2,3-cis-diol exposed. The 13C NMR spectra contained much weaker signals of the complexes, but both glycosides showed strong C-2 and C-3 alpha-shifts of +17.3 and +10.8 ppm, respectively. As expected, Me 2,3-Me(2)-alpha-Manp, which contains a 4,6-diol, did not complex. Me Galp anomers and their derivatives showed more diversity in the structure of its oxyvanadium derivatives. Me alpha-Galp, with its 3,4-cis-diol, complexed to give rise to 51V signals at delta -495 (9%), -508 (10%), and -534 (4%). These shifts and proportions were maintained with Me beta-Galp and Me 6Me-alpha-Galp. 51V NMR spectroscopy showed that Me 3Me-beta-Galp, with its possibly available 4,6-diol, did not complex. Similarly, Me alpha-Galp+vanadate gave a 13C DEPT spectrum that did not contain an inverted signal at delta >71.4, as would be expected of a C-6 resonance suffering a strong downfield alpha-shift. Me 2,6-Me(2)-alpha-Galp, with a 3,4-cis-diol group, gave rise to two 51V signals of complexes at delta -492 (9%) and -508 (9%), showing more than one structure of oxyvanadium derivatives.     

Synthesis of 2-O-benzyl- and 2,3- and 2,6-di-O-benzyl-D-galactose

The following ethers, of potential value for the synthesis of α-D-galactopyranosides, were prepared: 2-O-benzyl-D-galactose, 2,6-di-O-benzyl-D-galactose, and 2,3-di-O-benzyl-D-galactose. Isopropylidenation of methyl α-D-galactopyranoside in the presence of phosphorus pentaoxide gave its 3,4-, and 4,6-O-isopropylidene derivatives. Treatment of the 3,4-acetal with trityl chloride in pyridine produced the 6-trityl ether, which was benzylated with benzyl chloride and sodium hydride in N,N-dimethylformamide to yield the 2-benzyl ether. Acid hydrolysis of this product gave 2-O-benzyl-D-galactose. Benzylation of methyl 3,4-O-isopropylidene-α-D-galactopyranoside, followed by hydrolysis, gave 2,6-di-O-benzyl-D-galactose. Similarly, 2,3-di-O-benzyl-D-galactose was obtained by acid hydrolysis of methyl 2,3-di-O-benzyl-4,6-O-isopropylidene-α-D-galactopyranoside and of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-β-D-galactopyranoside.     

Biflavanoid proguibourtinidin carboxylic acids and their biflavanoid homologues from Acacia luederitzii

[4,6]- and [4,8]-Proguibourtinidin carboxylic acids (3,7,4′-trihydroxyl functionality) of 2,3-trans-3,4-trans: 2,3-cis- and 2,3-trans-3,4-trans: 2,3-trans-configuration based on (?)-epicatechin or (+)-catechin as constituent units, and their associated biflavanoid homologues, predominate in the heartwood of Acacia luederitzii. They are accompanied by stereochemical and functional analogues and by their putative flavan-3,4-diol and flavan-3-ol precursors.     

Regioselective C-3-O-acylation and O-methylation of 4,6-O-benzylidene-beta-D-gluco- and galactopyranosides displaying a range of anomeric substituents.

The regioselective C-3-O-acylation and O-methylation of a range of 4,6-O-benzylidene-beta-D-gluco- and galactopyranosides has been studied. Regioselectivity is achieved by forming the copper chelate of the 2,3-diol using either sodium hydride and copper(II) chloride, or copper(II) acetylacetanoate, or copper(II) acetate, prior to introduction of the acylating or methylating agent.     

Synthesis of beta-D-GlcA-(1----3)-beta-D-Gal disaccharides with 4- and 6-sulfate groups and 4,6-disulfate groups.

The sodium salts of the 6-sulfate 7, the 4-sulfate 10, and the 4,6-disulfate 12 of benzyl 3-O-(beta-D-glucopyranosyl uronate)-beta-D-galactopyranoside (5) have been synthesized. Methyl (2,3,4-tri-O-acetyl-1-bromo-1-deoxy-alpha-d-glucopyran)uronate (1) was coupled with benzyl 2-O-benzoyl-4,6-O-benzylidene-beta-D-galactopyranoside (2) to yield 3. The benzylidene acetal of 3 was hydrolyzed to give benzyl 2-O-benzoyl-3-O-[methyl (2,3,4-tri-O-acetyl-beta-D-glucopyranosyl)uronate]-beta-D-galactopyra noside (4). Compound 4 was utilized as a key intermediate to prepare the sulfated disaccharides 7,10, and 12. Direct sulfation of 4 with sulfur trioxide-trimethylamine for 2 days yielded the 6-sulfate 6. The 4,6-disulfate 11 was accessible by running the reaction under the same conditions for 14 days. The 4-sulfate 9 was obtained after protecting the 6-OH group of 4 by reaction with benzoyl imidazole to give the 6-benzoate 8, followed by sulfation under vigorous conditions. Treatment of the protected compounds 4, 6, 9, and 11 with aqueous sodium hydroxide in tetrahydrofuran gave the unprotected 5, 7, 10, and 12, respectively.     

Regioselective ring opening of benzylidene acetal protecting group(s) of hexopyranoside derivatives by DIBAL-H

The reductive ring-opening reaction of benzylidene-protected glucosides and mannosides such as methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-glucoside (1) and methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (4) by using a toluene stock solution of DIBAL-H and a dichloromethane stock solution of DIBAL-H gives mainly or selectively the corresponding 2,3,4-tri-O-benzyl derivatives (2, 5) and 2,3,6-tri-O-benzyl derivatives (3, 6), respectively, although that of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-d-galactoside (7) gives methyl 2,3,6-tri-O-benzyl-alpha-d-galactoside (9) selectively irrespective of the solvent of the stock solution of DIBAL-H. Similarly, the reaction of the exo-isomer of methyl 2,3:4,6-di-O-benzylidene-alpha-d-mannopyranosides (exo-10) with a toluene stock solution and dichloromethane stock solutions of DIBAL-H selectively gives methyl 3-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (12) and methyl 2-O-benzyl-4,6-O-benzylidene-alpha-d-mannoside (11), respectively, although that of endo-10 selectively affords 11, irrespective of the solvent of the stock solution of DIBAL-H.     

Synthesis of 2-acetamido-2-deoxy-3-O-β-d-mannopyranosyl-d-glucose

Condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-α-d-mannopyranosyl bromide with benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside (2) gave an α-d-linked disaccharide, further transformed by removal of the carbonyl and benzylidene groups and acetylation into the previously reported benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-glucopyranoside. Condensation of 3,4,6-tri-O-benzyl-1,2-O-(1-ethoxyethylidene)-α-d-glucopyranose or 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-glucopyranosyl bromide with 2 gave benzyl 2-acetamido-3-O-(2-O-acetyl-3,4,6-tri-O-benzyl-β-d-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside. Removal of the acetyl group at O-2, followed by oxidation with acetic anhydride-dimethyl sulfoxide, gave the β-d-arabino-hexosid-2-ulose 14. Reduction with sodium borohydride, and removal of the protective groups, gave 2-acetamido-2-deoxy-3-O-β-d-mannopyranosyl-d-glucose, which was characterized as the heptaacetate. The anomeric configuration of the glycosidic linkage was ascertained by comparison with the α-d-linked analog.     

The synthesis of racemic purpurosamine B

Starting from methyl 4,6-dichloro-4,6-dideoxy-α-D-galactopyranoside (1), D-chalcose (4,6-dideoxy-3-O-methyl-D-xcylo-hexopyranose) (5) was prepared by dechlorination with tributyltin hydride, selective benzoylation with benzoyl cyanide at O-2, methylation at O-3, and acid hydrolysis. D-Chalcose (5) was obtained as well by direct methylation of 1 with diazomethane at O-3, reduction with tin hydride, and hydrolysis. Chalcosyl bromide prepared from 5 was not very suitable for β-glycoside synthesis under Koenigs-Knorr conditions, and better results were obtained with 2- O-acetyl-4,6-dichloro-4,6-dideoxy-3-O-methyl-α-D-galactopyranosyl bromide, which gave β-glycosides with methanol, cyclohexanol, benzyl alcohol, 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, and methyl 2,3-di-O-benzyl-6-deoxy-α-D-glucopyranoside. After dechlorination with tributyltin hydride, the corresponding β-glycosides of D-chalcose were obtained in good yield.     

Synthesis and characterization of cis- and trans-2,3-epoxybutane-1,4-diol 1,4-bisphosphate,potential affinity labels for enzymes that bind sugar bisphosphates

cis- and trans-2,3-Epoxybutane-1,4-diol 1,4-bisphosphate, which can be considered reactive analogs of several sugar bisphosphates, have been synthesized in a continuing effort to develop new and diverse affinity labeling reagents for enzymes which bind phosphorylated substrates. cis-2,3-Epoxybutane-1,4-diol was obtained by epoxidation of commercially available cis-2-butene-1,4-diol with m-chloroperbenzoic acid; the trans epoxide was obtained by reduction of 2-butyne-1,4-diol with LiAlH₄ followed by epoxidation with m-chloroperbenzoic acid. The diols were phosphorylated with diphenyl chlorophosphate, and the phenyl blocking groups were then removed by Pt-catalyzed hydrogenation. By the criterion of their reaction with the sulfhydryl group of glutathione, the phosphorylated epoxides are 6000 times less electrophilic than the previously described and structurally similar reagent 3-bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate.     

DNA interstrand cross-linking by a mycotoxic diepoxide

The diepoxide mycotoxin (2R, 3R, 8R, 9R)-4,6-decadiyne-2,3:8,9-diepoxy-1,10-diol (repandiol) was both isolated from the mushroom Hydnum repandum and synthesized de novo. Repandiol was found to form interstrand cross-links within a restriction fragment of DNA, linking deoxyguanosines on opposite strands primarily within the 5'-GNC and 5'-GNNC sequences preferred by diepoxyoctane. However, repandiol was a significantly less efficient cross-linker than either of the diepoxyalkanes (diepoxyoctane and diepoxybutane) to which it was compared.     

Synthesis of p-nitrophenyl 6(5)-O-benzyl-alpha-maltopentaoside, a substrate for alpha amylases

p-Nitrophenyl alpha-maltopentaoside, having a benzyl group on O-6 of the terminal (nonreducing) D-glucosyl group was prepared by use of a reductive ring-opening reaction. Highly regioselective reduction of p-nitrophenyl O-(2,3-di-O-benzoyl-4,6-O-benzylidene-alpha-D-glucopyranosyl)-(1----4)- tris[O-(2,3,6-tri-O-benzoyl-alpha-D-glucopyranosyl)-(1----4)]-2,3,6-tri- O- benzoyl-alpha-D-glucopyranoside by dimethylamine-borane and p-toluenesulfonic acid, followed by debenzoylation, gave p-nitrophenyl O-(6-O-benzyl-alpha-D-glucopyranosyl)-(1----4)-tris[O-alpha-D-glucopyran osyl- (1----4)]-alpha-D-glucopyranoside. An experiment was done on the mode of action of human pancreatic and salivary alpha amylases on this derivative. The compound is suitable as a substrate for the assay of alpha amylase when used with glucoamylase and alpha-D-glucosidase as coupling enzymes.