Total synthesis of 3-O-[2-acetamido-6-O-(N-acetyl-alpha-D-neuraminyl-2-deoxy- alpha-D-galactosyl]-L-serine and a stereoisomer

O-(5-Acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-2- nonulopyranoxylonic acid)-(2----6)-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-(1----3) -L-serine, a structural unit occurring in various submaxillary mucins, was synthesized for the first time by using O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D- galacto-2-nonulopyranosyl)onate]-(2----6)-3,4-di-O-acetyl-2- azido-2-deoxy-D- galactopyranosyl trichloroacetimidate (13) and N-(benzyloxycarbonyl)-L-serine benzyl ester as the key intermediates. The trichloroacetimidate 13 was prepared by starting from two monosaccharide synthons, namely, allyl 2-azido-2-deoxy-beta-D-galactopyranoside and methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-beta-D- galacto-2-nonulopyranosyl chloride)onate, which were coupled in the presence of silver triflate in tetrahydrofuran to give the desired alpha-(2----6)-linked disaccharide in moderate selectivity.     

Synthesis of a fully protected derivative of O-(N-acetyl-alpha-D-neuraminyl)-(2----3)-O-beta-D-galactopyranosyl-(1- ---3)-O- [(N-acetyl-alpha-D-neuraminyl)-(2----6)]-O-(2-acetamido-2-deoxy-alpha- D-galactopyranosyl)-(1----3)-L-serine

N-(Benzyloxycarbonyl)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate]-(2----3)-O-(2,4,6-tri-O-acetyl-beta-D - galactopyranosyl)-(1----3)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-O-(2-acetamido-4-O-acetyl-2- deoxy-alpha-D- galactopyranosyl)-(1----3)-L-serine benzyl ester was synthesized by using O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5- di-deoxy-D-glycero-alpha-D-galacto-2-nonulopyranosyl)onate]- (2----3)-O-(2,4,6- tri-O-acetyl-beta-D-galactopyranosyl)-(1----3)-O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-4-O-acetyl-2-azido-2-deoxy-a lpha- and -beta-D-galactopyranosyl trichloroacetimidate as a key glycotetraosyl donor which, upon reaction with N-(benzyloxycarbonyl)-L-serine benzyl ester, afforded a 44% yield of a mixture of the alpha- and beta-glycosides in the ratio of 2:5.     

Synthesis of a mucin-type O-glycosylated amino acid, beta-Gal-(1----3)-[alpha-Neu5Ac-(2----6)]-alpha-GalNAc-(1----3)- Ser

Total synthesis of O-beta-D-galactopyranosyl-(1----3)-O-[(5-acetamido-3,5-dideoxy- D-glycero-alpha-D-galacto-2-nonulopyranosylonic acid)-(2----6)]-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-(1----3 )-L- serine was achieved by use of the key glycosyl donor O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1----3)-O- [methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galact o-2- nonulopyranosyl)onate-(2----6)]-4-O-acetyl-2-azido-2-deoxy-a lpha-D- galactopyranosyl trichloroacetimidate and the key glycosyl acceptor N-(benzyloxycarbonyl)-L- serine benzyl ester in a regiocontrolled way.     

Total synthesis of sialosylcerebroside, GM4

Described are total syntheses of O-[sodium (5-acetamido-3,5-dideoxy-D -glycero-alpha-D-galacto-2-nonulopyranosyl)onate]-(2----3)-O -beta-D -galactopyranosyl-(1----1)-(2R,3S,4E)-2-N-tetracosanoylsphingen ine,O-[sodium (5-acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosyl+ ++)onate] -(2----3)-O-alpha-D-galactopyranosyl-(1----1)-(2R,3S,4E)-2-N -tetracosanoylsphingenine, O-[sodium (5-acetamido-3,5-dideoxy-D-glycero-beta -D-galacto-2-nonulopyranosyl)onate]-(2----3)-O-beta-D-gal act opyranosyl -(1----1)-(2R,3S,4E)-2-N-tetracosanoylsphingenine, and O-[sodium (5-acetamido-3,5-dideoxy-D-glycero-beta-D-galacto-2-nonulopyranosyl++ +)onate] -(2----3)-O-alpha-D-galactopyranosyl-(1----1)-(2R,3S,4E)-2-N -tetracosanoylsphingenine by using O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D -galacto-2-nonulopyranosyl)onate]-(2----3)-2,3,4,6-tetra-O-a cetyl-D -galactopyrano-syl trichloroacetimidate and O-[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-beta -D-galacto-2-nonulopyranosyl)onate]-(2----3)-2,4,6-tri-O-ace tyl-D-galactopyranosyl trichloroacetimidate as key glycosyl donors, and (2S,3R,4E)-3 -O-benzoyl-2-N-tetracosanoylsphingenine as a key glycosyl acceptor.     

Synthesis of cerebroside, lactosyl ceramide, and ganglioside GM3 analogs containing beta-thioglycosidically linked ceramide

Coupling of the sodium salt of 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranose, -beta-D-galactopyranose, O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1----4)-2,3,6-tri-O- acetyl- 1-thio-beta-D-glucopyranose, or O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto -2- nonulopyranosylonate)-(2----3)-O-(2,3-di-O-acetyl-6-O-bezoyl -beta-D- galactopyranosyl)-(1----4)-3-O-acetyl-2,6-di-O-benzoyl-1-thio-beta-D- glucopyranose, which were prepared from the corresponding 1-S-acetates, 1, 3, 6, and 9, with (2S,3R,4E)-2-azido-3-O-benzoyl-1-O-(p-tolylsulfonyl)-4-oc tadecene-1,3-diol (12) derived by tosylation of 11, gave the corresponding beta-thioglycosides 13, 17, 21, and 25, respectively in good yield. The beta-thioglycosides obtained were converted, via selective reduction of the azide group, condensation with octadecanoic acid, and removal of the protecting groups, into the title compounds.     

Total synthesis of the modified ganglioside de-N-acetyl-GM3 and some analogs.

Methyl[methyl 4,7,8,9-tetra-O-acetyl-5-(tert-butoxycarbonylamino)-3,5- dideoxy-2-thio-D-glycero-alpha-D-galacto-2-nonulopyranosid]onat e was used for the glycosylation of benzyl O-(2,6-di-O-benzyl-beta-D-galactopyranosyl)- and benzyl O-(2,3-di-O-benzyl-beta-D-galactopyranosyl)-(1----4)-3,6-di-O-benzyl- 2-O-pivaloyl-beta-D-glucopyranoside to give benzyl O-[methyl 4,7,8,9-tetra-O-acetyl-5-(tert-butoxycarbonylamino)- 3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosylonate]-(2-- --3)-O-(2,6-di-O-benzyl-beta-D-galactopyranosyl)-(21) and benzyl O-[methyl 4,7,8,9-tetra-O-acetyl-5-(tert-butoxycarbonylamino)-3,5- dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosylonate]-(2----6) -O-(2,3-di- O-benzyl-beta-D-galactopyranosyl)-(1----4)-3,6-di-O-benzyl-2-O-pivaloyl- beta-D-glucopyranoside (18), respectively, accompanied by the beta-linked isomers 22 and 19, respectively. Compounds 18, 21, and 22 were converted into the corresponding glycotriosyl donors which, upon coupling with (2S,3R,4E)-3-O-benzoyl-2-N-tetracosanoylsphingenine, afforded completely protected ganglioside analogs 39, 40, and 41, respectively. Deprotection of 40, 41, and 39 completed the synthesis of the modified ganglioside de-N-acetyl-GM3, a stereoisomer, and a regioisomer. The N-deprotected forms of 40 and 39, on successive treatment with methyl isocyanate and O-deprotection, gave the N-(N-methylcarbamoyl) analogs of GM3 and its regioisomer.     

A regio- and stereo-controlled synthesis of beta-D-Glcp NAc6SO3-(1----3)-beta-D-Galp6SO3-(1----4)-beta-D-GlcpNAc 6SO3- (1----3)-D-Galp, a linear acidic glycan fragment of keratan sulfate I

A stereocontrolled synthesis of beta-D-GlcpNAc6SO3-(1----3)-beta-D-Galp6SO3-(1----4)-beta-D- GlcpNAc6SO3- (1----3)-D-Galp, was achieved by use of benzyl O-(2-acetamido-3,4 di-O-benzyl-2-deoxy-6-O-p-methoxyphenyl-beta-D- glucopyranosyl)-(1----3)-O-(2,4-di-O-tert-butyldiphenylsilyl-beta- D- galactopyranosyl-(1----4)-O-(2-acetamido-3-O-benzyl-2-deoxy-6-O-p-methox yphenyl - beta-D-glucopyranosyl)-(1----3)-2,4,6-tri-O-benzyl-beta-D-galactopyranos ide as a key intermediate, which was in turn prepared by employing two glycosyl donors, 3,4-di-O-benzyl-2-deoxy-6-O-p-methoxyphenyl-2-phthalimido-beta-D- glucopyranosyl trichloroacetimidate and O-(3,6-di-O-acetyl-2,4-di-O-benzyl-beta-D-galactopyranosyl)-(1----4)-3-O - benzyl-2-deoxy-6-O-p-methoxyphenyl-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate, and a glycosyl acceptor, benzyl 2,4,6-tri-O-benzyl-beta-D-galactopyranoside.     

Synthesis of aminoethylglycosides with oligosaccharide GM1 and asialo-GM1 ganglioside chains

4'-O-Glycosylation of 2-azidoethyl 2,3,6-tri-O-benzyl-4-O-(2,3-di-O- benzyl-6-O-benzoyl-beta-D-galactopyranosyl)-beta-D-glucopyranoside with a disaccharide donor, 4-trichloroacetamidophenyl 4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-beta-D- galactopyranosyl)-1-thio-2-trichloroacetamido-beta-D-galactopyranoside, in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid resulted in a tetrasaccharide, 2-azidoethyl (2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->3)- (4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido-beta-D-galactopyranosyl)- (1-->4)-(2,3-di-O-benzyl-6-O-benzoyl-beta-D-galactopyranosyl)- (1-->4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside, in 69% yield. The complete removal of O-protecting groups in the tetrasaccharide, the replacement of N-trichloroacetyl by N-acetyl group, and the reduction of the aglycone azide group to amine led to the target aminoethyl glycoside of beta-D-Gal- (1-->3)-beta-D-GalNAc-(1-->4)-beta-D-Gal-(1-->4)-beta-D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of asialo-GM1 ganglioside in 72% overall yield. Selective 3'-O-glycosylation of 2-azidoethyl 2,3,6-tri-O- benzyl-4-O-(2,6-di-O-benzyl-beta-D-galactopyranosyl)-beta-D-glucopyranoside with thioglycoside methyl (ethyl 5-acetamido-4,7,8,9-tetra-O- acetyl-3,5-dideoxy-2-thio-D-glycero-alpha-D-galacto-2-nonulopyranosyl)oate in acetonitrile in the presence of N-iodosuccinimide and trifluoroacetic acid afforded 2-azidoethyl [methyl (5-acetamido-4,7,8,9-tetra-O-acetyl- 3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosyl)oate in acetonitrile in the presence of N-iodosuccinimide and tri-fluoracetic acid afforded 2-azidoethyl[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl- 3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosyl) (2,6-di-O-benzyl-beta-D-galactopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D- glucopyranoside, the selectively protected derivative of the oligosaccharide chain of GM3 ganglioside, in 79% yield. Its 4'-O-glycosylation with a disaccharide glycosyl donor, (4-trichloroacetophenyl-4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O- acetyl-beta-D-galactopyranosyl) 1-thio-2-trichloroacetamido-beta-D-galactopyranoside in dichloromethane in the presence of N-iodosuccinimide and trifluoroacetic acid gave 2-azidoethyl (2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)- (1-->3)-(4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido-beta-D- galactopyranosyl)-(1-->4)-[[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D- galacto-2-nonulopyranosyl)onate]-(2-->3)]-(2,6-di-O-benzyl-beta-D- galactopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside in 85% yield. The resulting pentasaccharide was O-deprotected, its N-trichloroacetyl group was replaced by N-acetyl group, and the aglycone azide group was reduced to afford in 85% overall yield aminoethyl glycoside of beta-D-Gal-(1-->3)-beta-D-GalNAc-(1-->4)-[alpha-D-Neu5Ac-(2-->3)]- beta-D-Gal-(1-->4)-beta-D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of GM1 ganglioside. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 1; see also http://www.maik.ru.     

Synthesis of methyl glycoside derivatives of tri- and penta-saccharides related to the antithrombin III-binding sequence of heparin, employing cellobiose as a key starting-material

Two key synthons for the title pentasaccharide derivative, methyl O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L-idopyranosyluronate)-(1----4)-6-O-acetyl- 2-azido - 3-O- benzyl-2-deoxy-beta-D-glucopyranoside and O-(methyl 2,3-di-O-benzyl-4-O- chloroacetyl-beta-D-glucopyranosyluronate)-(1----4)-3,6-di-O-acetyl-2-az ido-2- deoxy-alpha-D- glucopyranosyl bromide, were prepared from a common starting material, cellobiose. They were coupled to give a tetrasaccharide derivative that underwent O-dechloroacetylation to the corresponding glycosyl acceptor. Its condensation with the known 6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl bromide afforded a 77% yield of suitably protected pentasaccharide, methyl O-(6-O- acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)- O- (methyl 2,3- di-O-benzyl-beta-D-glucopyranosyluronate)-(1----4)-O-(3,6-di-O-acetyl-2- azido-2 - deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2-O-benzoyl-3-O-benzyl-alpha-L- idopyranosyluronate)- (1----4)-6-O-acetyl-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranoside. Sequential deprotection and sulfation gave the decasodium salt of methyl O-(2- deoxy-2-sulfamido-6-O-sulfo-alpha-D-glucopyranosyl)-(1----4)-O-(be ta-D- glucopyranosyl-uronic acid)-(1----4)-O-(2-deoxy-2-sulfamido-3,6-di-O-sulfo-alpha-D-gluco pyranosyl)- (1----4)-O-(2-O-sulfo-alpha-L-idopyranosyluronic acid)-(1----4)-2-deoxy-2- sulfamido-6-O- sulfo-beta-D-glucopyranoside (3). In a similar way, the trisaccharide derivative, the hexasodium salt of methyl O-(2-deoxy-2-sulfamido-6-O-sulfo-alpha-D- glucopyranosyl)- (1----4)-O-(beta-D-glucopyranosyluronic acid)-(1----4)-2-deoxy-2-sulfamido-3,6- di-O- sulfo-alpha-D-glucopyranoside (4) was synthesized from methyl O-(6-O-acetyl-2- azido- 3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2,3-di-O- benzyl-beta- D-glucopyranosyluronate)-3,6-di-O-acetyl-2-azido-2-deoxy-alpha-D- glucopyranoside. The pentasaccharide 3 binds strongly to antithrombin III with an association constant almost equivalent to that of high-affinity heparin, but the trisaccharide 4 appears not to bind.     

Synthesis of novel ganglioside GM4 analogues containing N-deacetylated and lactamized sialic acid: probes for searching new ligand structures for human L-selectin

Novel ganglioside GM4 analogues, which contain N-deacetylated or lactamized sialic acid instead of usual N-acetylneuraminic acid, were synthesized in a highly efficient manner. (Methyl 4,7,8,9-tetra-O-acetyl-3,5-dideoxy-5-trifluoroacetamido-D-glycero-alpha-D-galacto-2-nonulopyranosylonate)-(2-->3)-4,6-di-O-acetyl-2-O-benzoyl-D-galactopyranosyl trichloroacetimidate was coupled with 2-(tetradecyl)hexadecanol to give the desired beta-glycoside in high yield. Successive O- and N-deacylation, and saponification of the methyl ester group afforded the N-deacetylated sialyl derivative that was converted by treatment with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride in Me2SO into the lactamized sialic acid-containing ganglioside GM4 analogue.     

Synthesis of a peripheral trisaccharide sequence of lutropin, a pituitary glycoprotein hormone; use of chitobiose as a key starting material

A chitobiose derivative, methyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-3,6 - di-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside, was derived from the corresponding N-acetyl derivative and this was converted into the glycosyl bromide (5). Glycosidation reaction between 5 and methyl 3,4,6-tri-O-benzyl-alpha-D-mannopyranoside in the presence of silver trifluoromethanesulfonate gave a beta-D-linked trisaccharide derivative. Replacement of the N,N-phthaloyl group by acetyl groups resulted in a product that was converted into methyl O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----4)-O -(2- acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----2)-3,4,6- tri-O- benzyl-alpha-D-mannopyranoside (11) by use of a few reaction steps. The 4(3)-hydroxyl group of 11 was methanesulfonylated, and the product subjected to SN2 replacement with acetate anion, to give the D-galactosamine-containing trisaccharide derivative (12). After basic hydrolysis of 12, the 4(3)-hydroxyl group was sulfated, and all benzyl groups were removed by hydrogenolysis, giving methyl O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-(1----4)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----2)-alpha-D-mannopyranosid e monosodium salt, the methyl alpha-glycoside derivative of the peripheral trisaccharide sequence of the pituitary glycoprotein hormone lutropin.     

Synthesis of a tetrasaccharide unit of the capsular polysaccharide of Streptococcus pneumoniae type 9V

In the synthesis of 8-methoxycarbonyloctyl O-(alpha-D-galactopyranosyl)-(1----3)-O-(2-acetamido-2-deoxy-beta-D- mannopyranosyl)-(1----4)-O-(beta-D-glucopyranosyl)-(1----4)-alpha-D- glucopyranoside, which represents a component of the capsular polysaccharide of Streptococcus pneumoniae type 9V, the key step was the coupling of alpha-D-Galp-(1----3)-beta-D-ManpNAc-(1----4)-D-Glc as glycosyl donor with 8-ethoxy-carbonyloctyl 6-O-acetyl-2,3-di-O-benzyl-alpha-D-glucopyranoside as glycosyl acceptor by use of the imidate method. Only the beta-imidate of the trisaccharide could be employed in this glycosidation reaction to give stereoselectively the tetrasaccharide in high yield. The alpha-imidate of the trisaccharide led to hydrolysis of the imidate group.     

Synthesis of an octasaccharide fragment of high-mannose-type glycans of glycoproteins.

O-(alpha-D-Mannopyranosyl)-(1----2)-O-(alpha-D-mannopyranosyl)-(1----3)- O- [(alpha-D-mannopyranosyl)-(1----2)-O-(alpha-D-mannopyranosyl)-(1----6)]- O- (alpha-D-mannopyranosyl)-(1----6)-O-(beta-D-mannopyranosyl)-(1----4)-O-( 2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----4)-2-acetamido-2-deoxy- glucopyranose, an octasaccharide fragment of high-mannose type glycan of glycoproteins, was synthesized. Crucial glycosylation of trisaccharide intermediate, benzyl O-(2,4-di-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-(2-acetamido-3,6-di -O- benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----4)-2-acetamido-3,6-di-O-benz yl-2- deoxy-beta-D-glucopyranoside, was successful only with a di-O-acetyltetradeca-O-benzyl-D-mannopentaosyl chloride. The use of the corresponding hexadeca-O-acetyl-D-mannopentaosyl bromide did not give the desired product.     

A facile synthesis of nitrophenyl oligosaccharides containing the O-alpha-L-fucopyranosyl-(1----3)-2-acetamido-2-deoxy-beta-D-glucopyrano syl unit at their nonreducing end.

A facile approach towards the synthesis of 4-nitrophenyl O-alpha-L-fucopyranosyl-(1----3)-2-acetamido-2-deoxy-beta-D-glucopyra nos ide, 2-nitrophenyl O-alpha-L-fucopyranosyl-(1----3)-O-(2-acetamido-2-deoxy-beta-D-glucop yra nosyl)- (1----6)-2-acetamido-2-deoxy-alpha-D-galactopyranoside, 4-nitrophenyl O-alpha-L-fucopyranosyl-(1----3)-O-(2-acetamido-2-deoxy-beta-D-glucop yra nosyl)- (1----6)-alpha-D-mannopyranoside, and 4-nitrophenyl O-alpha-L-fucopyranosyl-(1----3)-O-(2-acetamido-2-deoxy-beta-D-glucop yra nosyl)-(1----6)-beta-D-galactopyranoside has been accomplished through the development and use of methyl 3,4-O-isopropylidene-2-O-(4-methoxybenzyl)-1-thio-beta-L-fucopyranoside as the glycosyl donor.     

Synthesis of a branched pentasaccharide sequence of "bisected" structure of N-glycoproteins

For the synthesis of the threefold-branched pentasaccharide, O-alpha-D-mannopyranosyl-(1----3)-O-[(2-acetamido-2-deoxy-beta-D- glucopyranosyl)-(1----4)]-O-[alpha-D-mannopyranosyl-(1----6)]-O-beta-D- mannopyranosyl-(1----4)-2-acetamido-2-deoxy-D-glucopyranose (20), which is a part of the structure of the N-glycoproteins, the disaccharide 4-O-(4-O-acetyl-3,6-di-O-allyl-2-O-benzyl-beta-D-mannopyranosyl) -1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-beta-D-glucopyranose was synthesized as a key compound by use of the silver silicate-catalyst procedure. After elimination of the 4-O-acetyl group, a 2-acetamido-2-deoxy-beta-D-glucopyranosyl group was attached according to the phthalimido method. Further elimination of the allyl groups allowed the linkage of two alpha-D-mannopyranosyl groups in the presence of mercury salt. A deblocking sequence consisting of four steps gave 20.     

Synthesis of polydeoxygenated and iodinated disaccharides.]

3-Amino-polydeoxy disaccharides have been prepared by condensation of a glycal with methyl 2,3,6-trideoxy-alpha-L-erythro-(or threo)-hex-2-enopyranoside in the presence of N-iodosuccinimide. After acid hydrolysis of the glycoside, 1,4-addition of hydrazoic acid to the corresponding hex-2-enopyranose led to 3-azido-disaccharides which were acetylated. Reduction of the azido group gave 2,2'-dideoxy- or 2,2'-dideoxy-2'-iodo compounds. Condensation of O-(3,4-di-O-acetyl-2,6-dideoxy-2-iodo-alpha-L-manno-hexopy-rano syl)-(1----4)-1- O-acetyl-2,3,6-trideoxy-3-trifluoroacetamido-alpha-L-arabino-he xopyranose with daunomycinone, followed by 3',4'-O-deacetylation produced the new anthracycline, 7-O-[O-(2,6-dideoxy-2-iodo-alpha-L-manno-hexopyranosyl)-(1----4)-2,3,6- trideoxy-3-trifluoroacetamido-alpha-L-arabino-hexopyranosyl]-da uno-mycinone.     

Synthesis of modified tetrasaccharide sequences of N-glycoproteins

The tetrasaccharides O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D- mannopyranosyl-(1----6)]-O-(4-deoxy-beta-D-lyxo-hexopyranosyl)-(1- ---4)-2- acetamido-2-deoxy-alpha, beta-D-glycopyranose (22) and O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D-mannopyranosyl-(1----6)]-O- beta-D-talopyranosyl-(1----4)-2-acetamido-2-deoxy-alpha, beta-D- glucopyranose (37), closely related to the tetrasaccharide core structure of N-glycoproteins, were synthesized. Starting with 1,6-anhydro-2,3-di-O-isopropylidene-beta-D-mannopyranose, the glycosyl donors 3,6-di-O-acetyl-2-O-benzyl-2,4-dideoxy-alpha-D-lyxo- hexopyranosyl bromide (10) and 3,6-di-O-acetyl-2,4-di-O-benzyl-alpha-D-talopyranosyl bromide (30), were obtained in good yield. Coupling of 10 or 30 with 1,6-anhydro-2-azido-3-O-benzyl-beta-D-glucopyranose to give, respectively, the disaccharides 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2-O-benzyl-4 -deoxy- beta-D-lyxo-hexopyranosyl)-beta-D-glucopyranose and 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2,4-di-O-ben zyl- beta-D-talopyranosyl)-beta-D-glucopyranose was achieved with good selectivity by catalysis with silver silicate. Simultaneous glycosylation of OH-3' and OH-6' of the respective disaccharides with 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl chloride yielded tetrasaccharide derivatives, which were deblocked into the desired tetrasaccharides 22 and 37.     

Syntheses of the methyl glycosides of the repeating units of chondroitin 4- and 6-sulfate

3,4,6-Tri-O-acetyl-D-galactal was transformed into methyl 6-O-acetyl-2-azido-4-O-benzyl-2-deoxy-beta-D-galactopyranoside and its 4-O-acetyl-6-O-benzyl analogue, each of which was glycosylated with activated, O-acetylated derivatives of methyl D-glucopyranosyluronate. The resulting beta-(1----3)-linked disaccharide derivatives were each reductively N-acetylated, hydrogenolysed, O-sulfated, and saponified to afford the disodium salts of methyl 2-acetamido-2-deoxy-3-O-(beta-D-glucopyranosyluronic acid)-4-O-sulfo-beta-D-galactopyranoside and the 6-O-sulfo analogue. D-Galactal was also transformed into activated derivatives of 2-azido-3,6-di-O-benzyl-2-deoxy-D-galactopyranose and their 3,4-di-O-benzyl analogues with various substituents at O-4 and O-6. These glycosyl donors were condensed with 6-O-protected derivatives of methyl 2,3-di-O-benzyl-beta-D-glucopyranoside to give the beta-(1----4)-linked disaccharide derivatives, which were selectively deprotected, then oxidised at C-6 of the gluco unit, reductively N-acetylated, selectively deprotected, O-sulfated at C-4 or C-6 of the galacto unit, and hydrogenolysed to give the disodium salts of methyl 4-O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-beta-D- glucopyranosiduronic acid and the 6-O-sulfo analogue.     

Synthesis of the methyl thioglycosides of deoxy-N-acetyl-neuraminic acids for use as glycosyl donors.

Methyl 2-thioglycoside derivatives of 4-, 7-, 8-, and 9-deoxy-N-acetylneuraminic acids have been prepared as glycosyl donors for the synthesis of sialoglycoconjates. Reduction of a (phenoxy)thiocarbonyl group, selectively introduced at the 4 position of methyl [2-(trimethylsilyl)ethyl 5-acetamido-3,5-dideoxy-8,9-O-isopropylidene-D- glycero-alpha-D-galacto-2-nonulopyranosid]onate (1), gave the 4-deoxy compound, which was transformed via O-deisopropylidenation, acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, subsequent acetylation, and displacement of the 2-acetoxy group by a methylthio group, into methyl (methyl 5-acetamido-7,8,9-tri-O-acetyl-3,4,5-trideoxy-2-thio-D-manno-2- nonulopyranosid)onate (17). Methyl [2-(trimethylsilyl)ethyl 5-acetamido-8,9-di-O-acetyl-4-O-benzoyl- 3,5,7-trideoxy-alpha-D-galacto-2-nonulopyranosid]onate, prepared from 1 in five steps, and methyl [2-(trimethylsilyl)ethyl 5-acetamido-4,7,9-tri-O-acetyl-3,5,8-trideoxy-alpha-D-galacto-2- nonulopyranosid]onate, prepared from 1 in six steps, were converted via selective removal of the 2-(trimethylsilyl)ethyl group, O-acetylation, and displacement of the 2-acetoxy group by a methylthio group as described for 17, into the corresponding methyl 7- and 8-deoxy-2-thioglycosides. Reductive dechlorination of methyl [2-(trimethylsilyl)ethyl 5-acetamido-4,7-di-O-benzoyl-9-chloro-3,5,9-trideoxy-D-glycero-alpha-D-g alacto- 2-nonulopyranosid]onate, prepared from methyl [2-(trimethylsilyl)ethyl 5-acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosid++ +]onate by selective 9-O-tert-butyldimethylsilylation, benzoylation, removal of the 9-silyl group, and selective chlorination, gave a 9-deoxy compound. This was transformed, via O-debenzoylation, O-acetylation, selective removal of the 2(trimethylsilyl)ethyl group, 2-O-acetylation, 2-chlorination, displacement with potassium thioacetate, selective S-deacetylation, and S-methylation, into the methyl 2-thio-alpha-glycoside of 9-deoxy-N-acetylneuraminic acid.     

Synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp+ ++-(1----6)] - beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp- (1----6)]-D- GlcpNAc, a core glycoheptaose of a "bisected" complex-type glycan of glycoproteins

A synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp++ +-(1----6)]- beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp-( 1----6)]-D- GlcpNAc was achieved by employing benzyl O-(3,4,6-tri-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-O- (2-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-(3,6-di-O-benzyl-2-deoxy-2 - phthalimido-beta-D-glucopyranosyl)-(1----4)-3-O-benzyl-2-deoxy-6-O-p- methoxyphenyl-2-phthalimido-beta-D-glucopyranoside as a key glycosyl acceptor. Highly stereoselective mannosylation was performed by taking advantage of the 2-O-acetyl group in the mannosyl donors. The alpha-L-fucopyranosyl residue was also stereoselectively introduced by copper(II)-mediated activation of methyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside.