Chemistry of glycosylamines. Isopropylidene acetals of N-acetyl-α-d-glucofuranosylamine

The reaction of N-acetyl-α-d-glucofuranosylamine with 2,2-dimethoxypropane, catalyzed by p-toluenesulfonic acid, gave 1-acetamido-2,3:5,6-di-O-isopropylidene-1-O-methyl-d-glucitol (65.6%), 1-acetamido-2,3-O-isopropylidene-1-O-methyl-d-glucitol (3.7%), and N-acetyl-5,6-O-isopropylidene-α-d-glucofuranosylamine (3.2% yield). The structures of these compounds were determined by chemical and spectroscopic methods, and their relation to the pattern of n.m.r. resonances of the isopropylidene methyl groups is discussed.     

Syntheses of 2-acetamido-2-deoxy-4-O-α-D-glucopyranosyl-α-d-glucopyranose (n-acetylmaltosamine) and 2-acetamido-2-deoxy-4-O-β-d-glucopyranosyl-α-d-glucopyranose

Condensation of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside with 2,3,4,6-tetra-O-benzyl-1-O-(N-methyl)acetimidoyl-β-D-glucopyranose gave benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-α-D-glucopyranoside which was catalytically hydrogenolysed to crystalline 2-acetamido-2-deoxy-4-O-α-D-glucopyranosyl-α-D-glucopyranose (N-acetylmaltosamine). In an alternative route, the aforementioned imidate was condensed with 2-acetamido-3-O-acetyl-1,6-anhydro-2-deoxy-β-D-glucopyranose, and the resulting disaccharide was catalytically hydrogenolysed, acetylated, and acetolysed to give 2-acetamido-1,3,6-tri-O-acetyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)-α-D-glucopyranose Deacetylation gave N-acetylmaltosamine. The synthesis of 2-acetamido-2-deoxy-4-O-β-D-glucopyranosyl-α-D-glucopyranose involved condensation of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide in the presence of mercuric bromide, followed by deacetylation and catalytic hydrogenolysis of the condensation product.     

The synthesis,and study of the β-elimination reaction,of di- and tri-peptides having a 3-O(2-acetamido-3,4,6-trio-O-acetyl-2-deoxy-β-D-glucopyranosyl)-L-serine residue

2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyra-nosyl chloride was condensed with the N-(benzyloxycarbonyl) derivatives of, respectively, L-seryl-glycine ethyl, L-seryl-L-alanine methyl, L-seryl-L-phenylalanine methyl, and L-seryl-L-aspartic dibenzyl esters to give (3-O-GlcpNAc-CbzN-L-Ser)-GlyOEt (8), (3-O-GlcpNAc-CbzN-L-Ser)-L-AlaOMe (9), (3-O-GlcpNAc-CbzN-L-Ser)-L-PheOMe (10), and (3-O-GlcpNAc-CbzN-L-Ser)-L-Asp(diOBzl) (11), respectively; O-(2-acetamido-3,4,6-tri-O-acetyl-β-D-glucopyranosy-l)-N-(benzyloxycarbonyl)-L-serine methyl ester was deblocked by treatment with hydrobromic acid in glacial acetic acid, followed by triethylamine, to give a glycoamino acid that was condensed with the N-(benzyloxycarbonyl) derivatives of the p-nitrophenyl ester of glycine, L-alanine, and L-proline, respectively, to give CbzNGly-(3-O)-Glcp NAc-L-SerOMe) (17), CbzN-L-Ala-(3-O-GlcpNAc-L-SerOMe), and CbzN-L-Pro-(3-O-GlcpNAc-L-SerOMe), respectively. Similarly, the glycopeptide resulting from 8 was condensed with the activated esters of glycine, L-alanine, L-phenylalanine, L-proline, and L-serine, respectively, to give CbzNGly-(3-OGlcpNAc-L-Ser)-GlyOEt, CbzN-L-Ala-(3-O-GlcpNAc-L-Ser)-GlyOEt, CbzN-L-Phe-(3-O-GlcpNAc-L-Ser)-GlyOEt, and CbzN-L-Ser-(3-O-GlcpNAc-L-Ser)-GlyOEt, respectively; that from 9, with the p-nitrophenyl esters of glycine¹,L-alanine, L-phenylalanine, L-proline, and L-leucine, respectively, to give CbzNGly-(3-O-GlcpNAc-L-Ser)-L-AlaOMe, CbzN-L-Ala(3-O-GlcpNAc-L-Ser)-L-AlaOMe, CbzN-L-Phe-(3-O-GlcpNAc-L-Ser)-L]-AlaOMe, CbzN-L-Pro-(3-O-GlcpNAc-L-Ser)-L-AlaOMe, and CbzN-L-Leu-(3-O-GlcpNAc- L-Ser)-L-AlaOMe, respectively; that from 10, with the derivatives of glycine, L-alanine, L-phenylalanine, and L-leucine, respectively, to give CbzNGly-(3-O-GlcpNAc-L-Ser)-L-PheOMe, CbzN-L-Phe-(3-O-GlcpNAc-L-Ser)-L-PheOMe, CbzN-L-Phe-(3-O-GlcpNAc-L-Ser)-L-PheOMe, and CbzN-L-Leu-(3-O-GlcpNAc-L-Ser)-L-PheOMe, respectively; and that from 11, with the derivatives of glycine, L-alanine, L-phenylalanine, L-proline, and L-leucine, respectively, to give CbzNGly-(3-O-GlcpNAc-L-Ser)-L-Asp(diOBzl), CbzN-L-Ala-(3-O-GlcpNAc-L-Ser)-L-Asp(diOBzl), CbzN-L-Phe-(3-O-GlcpNAc-L-Ser)-L-Asp(diOBzl), CbzN-L-Pro-(3-O-GlcpNAc-L-Ser)-L-Asp(diOBzl), and CbzN-L-Leu-(3-O-GlcpNAc-L-Ser)-L-Asp-(diOBzl), respectively. O-(2-Acetamido-3,4,5-tri-O-acetyl-2-deoxy-β-D-gluco-pyranosyl)-N-(benzyloxycarbonyl)- L-asparaginylglycyl-L-serine methyl ester (20) was synthesized by treating the free amine of 17 with the p-nitrophenyl ester of N-(benzyloxycarbonyl)-L-asparagine. 2-Acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbo-nyl)-L-aspart-1-oyl-(glycyl-L-serine methyl ester)-4-oyl]-2-deoxy-β-D-glucopyranosylamine (41) was synthesized by the condensation of 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbo-nyl)-L-aspart-4-oyl]-2-deoxy-β-D-glucopyranosylamine with glycyl-L-serine methyl ester. Attempts to transfer the 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-D-glucopyranosyl group from the hydroxyl group of L-serine in 20 to the amido group of L-asparagine, to give 41, were unsuccessful. The β-elimination of some of the glycodi- and glycotri-peptides was studied.     

The synthesis of oligosaccharide-asparagine compounds. V. O- -D-mannopyranosyl-(1 leads to 6)-O-(2-acetamido-2-deoxy- -D-glucopyranosyl)-(1 leads to 4)-2-acetamido-N-(L-aspart-4-oyl)-2-deoxy- -D-glucopyranosylamine

O-α-d-Mannopyranosyl-(1→6)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→4)-2-acetamido-N-(l-aspart-4-oyl)-2-deoxy-β-d-glucopyranosylamine (12), used in the synthesis of glycopeptides and as a reference compound in the structure elucidation of glycoproteins, was synthesized via condensation of 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide with 2-acetamido-4-O-(2-acetamido-3-O-acetyl-2-deoxy-β-d-glucopyranosyl)-3,6-di-O-acetyl-2-deoxy-β-d-glucopyranosyl azide (5) to give the intermediate, trisaccharide azide 7. [Compound 5 was obtained from the known 2-acetamido-4-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-3,6-di-O-acetyl-2-deoxy-β-d-glucopyranosyl azide by de-O-acetylation, condensation with benzaldehyde, acetylation, and removal of the benzylidene group.] The trisaccharide azide 6 was then acetylated, and the acetate reduced in the presence of Adams' catalyst. The resulting amine was condensed with 1-benzyl N-(benzyloxycarbonyl)-l-aspartate, and the O-acetyl, N-(benzyloxycarbonyl), and benzyl protective groups were removed, to give the title compound.     

The relationship of molecular weight, and sulfate content and distribution to anticoagulant activity of heparin preparations

The crystalline intermediate 2-acetamido-6-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-glucopyranosyl)-3,4-di-O-acetyl-2-deoxy-β-D-glucopyranosyl azide (5), obtained by condensation of 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-glucopyranosyl bromide with either 2-acetamido-3,4-di-O-acetyl-2-deoxy-β-D-glucopyranosyl azide or its 6-O-triphenylmethyl derivative, was reduced in the presence of Adams' catalyst to give a disaccharide amine. Condensation with 1-benzyl N-(benzyloxycarbonyl)-L-aspartate afforded crystalline 2-acetamido-6-O-(2-acetamido-3,4 6-tri-O-acetyl-2-deoxy-β-D-glucopyranosyl)-3,4-di-O-acetyl-1-N-[1-benzyl N-(benzyloxycarbonyl)-L-aspart-4-oyl]-2-deoxy-β-D-glucopyranosylamine (9). Catalytic hydrogenation in the presence of palladium-on-charcoal was followed by saponification to give 2-acetamido-6-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-1-N-(L-aspart-4-oyl)-2-deoxy-β-D-glucopyranosylamine (11) in crystalline form. From the mother liquors of the reduction of 5, a further crystalline product was isolated, to which was assigned a bisglycosylamine structure (12).     

The attachment of poly(ribitol phosphate) to lipoteichoic acid carrier

2-Acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl)-L-aspart-1-oyl-(L-leucyl-L-threonyl-N²-tosyl-L-lysine p-nitrobenzyl ester)-4-oyl]-2-deoxy-β-D-glucopyranosylamine (21) and 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl)-L-aspart-1-oyl-(L-leucyl-L-threonyl-N²-tosyl-L-lysine p-nitrobenzyl ester)-4-oyl]-2-deoxy-β-D-glucopyranosylamine (22), 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl)-L-aspart-1-oyl-(glycine ethyl ester)-4-oyl]-2-deoxy-β-D-glucopyranosylamine, and 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl)-L-aspart-1-oyl-(phenylalanine methyl ester)-4-oyl]-2-deoxy-β-D-glucopyranosylamine were synthesized by condensation of 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(benzyloxycarbonyl)-L-aspart-4-oyl]-2-deoxy-β-D-glucopyranosylamine with the appropriate protected amino acids and tri- and tetra-peptides. The amino acid sequences of 21 and 22 correspond to the protected amino acid sequences 34–37 and 34–38 of ribonuclease B that are adjacent to the carbohydrate-protein linkage.     

Novel route to chaetomellic acid A and analogues: Serendipitous discovery of a more competent FTase inhibitor

A new practical route to chaetomellic acid A (ACA), based on the copper catalysed radical cyclization (RC) of (Z)-3-(2,2-dichloropropanoyl)-2-pentadecylidene-1,3-thiazinane, is described. Remarkably, the process entailed: (i) a one-pot preparation of the intermediate N-α-perchloroacyl-2-(Z)-alkyliden-1,3-thiazinanes starting from N-(3-hydroxypropyl)palmitamide, (ii) a two step smooth transformation of the RC products into ACA and (iii) only one intermediate chromatographic purification step. The method offers a versatile approach to the preparation of ACA analogues, through the synthesis of an intermediate maleic anhydride with a vinylic group at the end of the aliphatic tail, a function that can be transformed through a thiol–ene coupling. Serendipitously, the disodium salt of 2-(9-(butylthio)nonyl)-3-methylmaleic acid, that we prepared as a representative sulfurated ACA analogue, was a more competent FTase inhibitor than ACA. This behaviour was analysed by a molecular docking study.     

Photochemical addition of 1,3-dioxolane and of 2-propanol to 1,2,4,6-tetra-O-acetyl-3-deoxy-α- and -β-D-erythro-hex-2-enopyranose

Photoirradiation of a solution of 1,2,4,6-tetra-O-acetyl-3-deoxy-β-D-erythro-hex-2-enopyranose (1) in 1:50 acetone-1,3-dioxolane with a high-pressure mercury-lamp, followed by chromatographic separation, gave 1,2,4,6-tetra-O-acetyl-3-deoxy-3-C-(1,3-dioxolan-2-yl)-β-D-glucopyranose (3) (44%) and-mannopyranose (4) (35%). Similar treatment of the α anomer (2) of 1 afforded 1,2,4,6-tetra-O-acetyl-3-deoxy-3-C-(1,3-dioxolan-2-yl)-α-D-glucopyranose (5) (38%), -mannopyranose (6) (31%), and -allopyranose (7) (21%).On the other hand, irradiation of 2 in 1:100 acetone-2-propanol gave 1,2,4,6-tetra-O-acetyl-3-deoxy-3-C-(1-hydroxy-1-methylethyl)-α-D-mannopyranose (8) (76%). Moreover, irradiation of 2 in 1:1 acetone-2-propanol yielded 1,4,6-tri-O-acetyl-3-deoxy-2,3-di-C-(1-hydroxy-1-methylethyl)-α-D-gluco- or -manno-pyranose 2,2¹,3¹-orthoacetate (10) (15%), in addition to 8 (44%).     

Chemical modification of aminocyclitol antibiotics

The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystreptamine moiety. The partially acetylated neamine derivatives, 6,3′,4′-tri-O-acetyl- (3) and 5,3′,4′-tri-O-acetyl-1,3,2′,6′-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-d-ribofuranosyl chloride led to 6-O-(β-d-ribofuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide afforded the corresponding 6-O-(d-hexopyranosyl)neamines.     

Synthesis of carbon-11-labeled CK1 inhibitors as new potential PET radiotracers for imaging of Alzheimer’s disease

The reference standards methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate (5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-methoxybenzamide (5c), and their corresponding desmethylated precursors 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoic acid (6a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-hydroxybenzamide (6b), were synthesized from 5-amino-2,2-difluoro-1,3-benzodioxole and 3-substituted benzoic acids in 5 and 6 steps with 33% and 11%, 30% and 7% overall chemical yield, respectively. Carbon-11-labeled casein kinase 1 (CK1) inhibitors, [¹¹C]methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate ([¹¹C]5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-[¹¹C]methoxybenzamide ([¹¹C]5c), were prepared from their O-desmethylated precursor 6a or 6b with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–45% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.     

Synthesis of 4-thio-dD-mannose

1,6-Anhydro-4-S-benzoyl-4-thio-β-D-mannopyranose, obtained by treatment of 1,6:3,4-dianhydro-β-D-talopyranose with pyridinium thiolbenzoate in N,N-di-methylformamide, was converted into its 2,3-di-O-acetyl derivative, which was acetolyzed to give 1,2,3,6-tetra-O-acetyl-4-S-benzoyl-4-thio-D-mannopyranose. Deacylation of the last-named compound with sodium methoxide in methanol gave syrupy 4-thio-D-mannose, which was characterized as 1,2,3,5,6-penta-O-acetyl-4-thio-α- and -β-D-mannofuranose.     

Enzyme models. The attachment of N-methylhydroxamic acid to cyclohexaamylose. Its reactivity and specificity with phenyl esters

The N-methylacetohydroxamic acid group has been introduced into cyclohexaamylose by the following sequence of reactions: (1) carboxymethylation of cyclohexaamylose by iodoacetic acid, (2) methylation of carboxymethylcyclohexaamylose with diazomethane, and (3) reaction of the carboxymethylcyclohexaamylose methyl ester with N-methylhydroxylamine to form the N-methylacetohydroxamic acid-substituted cyclohexaamylose. By employing purification procedures involving ionexchange chromatography, the synthesis yielded a mono-substituted cyclohexaamylose-N-methylacetohydroxamic acid with selective modification of the C-2, C-3 hydroxyl group side of the cyclohexaamylose ring.p-Nitrophenyl acetate and 2-hydroxy-5-nitro-α-toluenesulfonic acid sultone react 20- and 70-fold faster with cyclohexaamylose-N-methylacetohydroxamic acid than with N-methylmethoxyacetohydroxamic acid. Cyclohexaamylose-N-methylacetohydroxamic acid also displays a marked kinetic stereospecificity for p-nitroover m-nitrophenyl acetate (whereas cyclohexaamylose itself exhibits the reverse stereospecificity). These reactions were shown to be competitively inhibited by cyclohexanol. This evidence indicates that cyclohexaamylose-N-methylacetohydroxamic acid binds the substrate in a reversible complexation step prior to nucleophilic attack and thus is an enzyme model.     

New structures and composition of cell wall teichoic acids from Nocardiopsis synnemataformans,Nocardiopsis halotolerans,Nocardiopsis composta and Nocardiopsis metallicus: a chemotaxonomic value

The structures of the cell wall teichoic acids (TA) from some species of the genus Nocardiopsis were established by chemical and NMR spectroscopic methods. The cell walls of Nocardiopsis synnemataformans VKM Ac-2518^T and Nocardiopsis halotolerans VKM Ac-2519^T both contain two TA with unique structures—poly(polyol phosphate-glycosylpolyol phosphate)—belonging to the type IV TA. In both organisms, the minor TA have identical structures: poly(glycerol phosphate-N-acetyl-β-galactosaminylglycerol phosphate) with the phosphodiester bond between C-3 of glycerol and C-4 of the amino sugar. This structure is found for the first time. The major TA of N. halotolerans has a hitherto unknown structure: poly(glycerol phosphate-N-acetyl-β-galactosaminylglycerol phosphate), the N-acetyl-β-galactosamine being acetalated with pyruvic acid at positions 4 and 6. The major TA of N. synnemataformans is a poly(glycerol phosphate-N-acetyl-β-galactosaminylglycerol phosphate) with the phosphodiester bond between C-3 of glycerol and C-3 of the amino sugar. The cell walls of Nocardiopsis composta VKM Ac-2520 and N. composta VKM Ac-2521^T contain only one TA, namely 1,3-poly(glycerol phosphate) partially substituted with N-acetyl-α-glucosamine. The cell wall of Nocardiopsis metallicus VKM Ac-2522^T contains two TA. The major TA is 1,5-poly(ribitol phosphate), each ribitol unit carrying a pyruvate ketal group at positions 2 and 4. The structure of the minor TA is the same as that of N. composta. The results presented correlate well with the phylogenetic grouping of strains and confirm the species and strain specific features of cell wall TA in members of the genus Nocardiopsis.     

A synthetic approach to polysialogangliosides containing α-sialyl-(2 → 8)-sialic acid: total synthesis of ganglioside GD3

A stereocontrolled, facile total synthesis of ganglioside GD₃ is described as an example of a proposed systematic approach to the preparation of gangliosides containing an α-sialyl-(2 → 8)-sialic acid unit α-glycosidically linked to O-3 of a d-galactose reesidue in their oligosaccharide chains. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-, 3-O-benzoyl-, or 3-O-benzyl-β-d-galactopyranosides, or 2-(trimethylsilyl)ethyl 2,3,6,2′,6′-penta-O-benzyl-β-lactoside (7), with methyl [phenyl 5-acetamido-8-O-(5-acetamido-4,7,8,9- tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosyl-ono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-2-thio- d-glycero-d-galacto-2-nonulopyranosid]onate (3), using N-iodosuccinimide-trifluoromethanesulfonic acid as a promoter, gave the corresponding α glycosides 8 (32%), 13 (33%), 14 (48%), and 17 (31%), respectively. The glycyl donor 3 was prepared from O-(5-acetamido-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonic acid)-(2 → 8)-5-acetamido-3,5-dideoxy-d-glycero- d-galacto-2-nonulopyranosonic acid by treatment with Amberlite IR-120 (H⁺) in methanol, O-acetylation, and subsequent replacement of the anomeric acetoxy group with phenylthio. Compound 8 was converted into the methyl β-thioglycoside via O-benzoylation, replacement of the 2-(trimethylsilyl)ethyl group by acetyl, and introduction of the methylthio group by reaction with methylthiotrimethylsilane. Compound 17 was converted, via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the α-trichloroacetimidate, which was coupled with (2S,3R,4E)-2-azido-3O-benzoyl-4-octadecene-1,3-diol to give the β-glycoside. This glycoside was easily transformed, via selective reduction of the azido group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester and lactone functions, into ganglioside GD₃.     

The synthesis of a mannosyl-N-acetylglucosamine-l-asparagine compound: 2-acetamido-N-(l-aspart-4-oyl)-2-deoxy-3-O-α-d-mannopyranosyl-β-d-glucopyranosylamine

The title compound, used in the synthesis of glycopeptides and as a reference substance in the structural elucidation of glycoproteins, was synthesized by condensation of 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide with 2-acetamido-4,6-O-benzylidene-α-d-glucopyranosyl azide, followed by removal of the benzylidene group to give the disaccharide azide 6 and acetylation. The resulting fully acetylated disaccharide azide 7 was also obtained by treatment of the known 2-acetamido-1,4,6-tri-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-glucopyranose with hydrogen chloride and then with silver azide. The azide 7 was reduced in presence of platinum oxide (Adams' catalyst), and the resulting amine was condensed with 1-benzyl N-benzyloxycarbonyl-l-aspartate in the presence of N,N′-dicyclocarbodiimide. The removal of the protective group was accomplished by hydrogenolysis and O-deacetylation. In a second route, the disaccharide azide 6 was reduced and then condensed with 1-benzyl N-benzyloxycarbonyl-l-aspartate, and the resulting product hydrogenolyzed.     

Synthesis and glycosidation of 1-deoxy-1-[(2,2-diacylvinyl)amino]-d-fructoses

The reactions of 1-amino-1-deoxy-d-fructose acetate (1) with methyl 3-methoxy-2-methoxycarbonylacrylate and 5-methoxymethylene-2,2-dimethyl-1,3-dioxane-4,6-dione in the presence of a base afforded 1-deoxy-1-[(2,2-dimethoxycarbonylvinyl)amino]- (2 and 1-deoxy-1-[(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidenemethyl)amino]-d-fructose (3), respectively, in high yields. 1-Deoxy-1-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)amino]-d-fructose (4) was obtained (85%) by a transamination reaction between 1 and 5,5-dimethyl-2-phenylaminomethylene-1,3-cyclohexanedione in the presence of Et₃N. The isomeric composition of equilibrium solutions of 1–4 was established by ¹³C-n.m.r. spectroscopy. For all the compounds, the β-pyranose form was the main component in D₂O; the α-furanose, the β-furanose, and, for 1, the α-pyranose forms, were also present. The major constituents of 2 in (CD₃)₂SO solution were the β- and the α-furanose forms. Acetylation of 2 afforded the tetra-acetates of the α- and β-furanose forms, the 3,4,6-triacetates of the α- and β-furanose forms, the 3,4,5-triacetate of the β-pyranose form, and 2,3,4,5,6-penta-O-acetyl-1-deoxy-1-[(2,2-dimethoxycarbonylvinyl)amino]-d-arabino-hex-1-enitol. Glycosidation of 2 with MeOHHCl afforded a mixture of methyl 1-deoxy-1-[(2,2-dimethoxycarbonylvinyl)amino]-α- (11α) and -β-d-fructofuranoside (11β), and methyl 1-deoxy-1-[(2,2-dimethoxycarbonylvinyl)-amino]-β-d-fructopyranoside (13). Compounds 11α and 13 were isolated as their tri-acetates (12 and 14, respectively). Deacetylation and removal of the N-protecting group of 12 gave methyl 1-amino-1-deoxy-α-d-fructofuranoside (∼54% from 2).     

13C-N.M.R.-Spectral study of the mode of binding of Mn2+ and Gd3+ to N-acetyl-α-neuraminic acid

Natural-abundance, ¹³C-n.m.r. spectroscopy was used to study the binding of Gd³⁺ and Mn²⁺ to N-acetyl-2-O-methyl-α-neuraminic acid (2) and to methyl N-acetyl-2-O-methyl-α-neuraminate (3). The results showed that Gd³⁺ and Mn²⁺ bind in the region of the glycerol-1-yl side-chain and the 5-acetamido group of compound 3. When the α-NeuAc derivative contains a carboxylate anion, as in compound 2, multiple, metal-ion-binding sites occur, involving the head (the carboxyl end) and the tail (the glycerol-1-yl and 5-acetamido groups) of the molecule.     

Interaction ofN-acetyl-4-, 7-, 8- or 9-deoxyneuraminic acids andN-acetyl-4-, 7- or 8-mono-epi- and-7,8-di-epineuraminic acids withN-acetylneuraminate lyase

Various deoxy- and epi-derivatives ofN-acetylneuraminic acid were synthesized and tested for their substrate properties withN-acetylneuraminate lyase fromClostridium perfringens.N-Acetyl-9-deoxyneuraminic acid is a good substrate,N-acetylneuraminic acid derivatives with epimeric configuration at C-7, C-8 or both are cleaved slowly, whileN-acetyl-4-epi-,N-acetyl-4-deoxy-,N-acetyl-7-deoxy-andN-acetyl-8-deoxyneuraminic acid are resistant to enzyme action.N-Acetyl-4-deoxyneuraminic acid andN-acetyl-4-epineuraminic acid competitively inhibit the enzyme. These studies give further insight into a mechanism proposed for the reversible cleavage of sialic acids byN-acetylneuraminate lyase.     

Design,synthesis and biological evaluation of N-arylphenyl-2,2-dichloroacetamide analogues as anti-cancer agents

Our earlier research has shown that N-phenyl-2,2-dichloroacetamide analogues had much higher anti-cancer activity than the lead compound sodium dichloroacetate (DCA). In this current study, a variety of N-arylphenyl-2,2-dichloroacetamide analogues were synthesized via Suzuki coupling reaction and their anti-cancer activity was evaluated. The results showed that N-terphenyl-2,2-dichloroacetamide analogues had satisfactory anti-cancer activity. Among them, N-(3,5-bis(benzo[d][1,3]dioxol-5-yl)phenyl)-2,2-dichloroacetamide (6 k) had an IC₅₀ of 2.40 μM against KB-3-1 cells, 1.04 μM against H460 cells and 1.73 μM against A549 cells.     

Blocksynthese von O-glycopeptiden und anderen T-antigen strukturen

Under the conditions of in situ anomerisation, the 2-azido-4,6-di-O-benzoyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranosyl bromide reacted directly and with high selectivity with the reactive hydroxyl groups of l-serine and l-threonine derivatives to form α-glycosidically-linked products. Thus, the glycopeptides containing l-serine and l-threonine are more accessible. The disaccharide block could also be coupled with other reactive hydroxyl compounds to give compounds that contain the T-receptor.