An effective synthesis of an arabinogalactan with a beta-(1-->6)-linked galactopyranose backbone and alpha-(1-->2) arabinofuranose side chains

An octasaccharide, beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->2)]-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->5)-alpha-L-Araf-(1-->2)]-beta-D-Galp-(1-->6)-beta-D-Galp-1-->OMP was synthesized. 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (5), 2,6-di-O-acetyl-3,4-di-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (9), and 4-methoxyphenyl 2-O-acetyl-3,4-di-O-benzoyl-beta-D-galactopyranoside (11), 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (12), and 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (17) were used as the synthons. A concise route was used to gain the tetrasaccharide donor 19 by the use of 11, 12, 5, and 17. Meanwhile, treatment of 5 with 9 yielded beta-(1-->6)-linked disaccharide 20, and subsequent selective 6-O-deacetylation produced the disaccharide acceptor 21. Reaction of 21 with 19 gave 22, and subsequent selective 2-O-deacetylation afforded the hexasaccharide acceptor 23. Condensation of 23 with alpha-L-(1-->5)-linked arabinofuranose disaccharide 24, followed by deprotection, yielded the target octasaccharide.     

Concise syntheses of arabinogalactans with beta-(1-->6)-linked galactopyranose backbones and alpha-(1-->3)- and alpha-(1-->2)-linked arabinofuranose side chains

4-methoxyphenyl glycosides of 2,3'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl tetraose (16), 3',2'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl hexaose (27), and a twentyose (42) consisting of beta-(1-->6)-linked D-galactopyranosyl pentadecaoligosaccharide backbone with alpha-L-arabinofuranosyl side chains alternately attached at C-2 and C-3 of the middle galactose residue of each consecutive beta-(1-->6)-linked galactotriose unit of the backbone, were synthesized with isopropyl 3-O-allyl-2,4-di-O-benzoyl-1-thio-beta-D-galactopyranoside (6), 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (7), 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (12), 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (17), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (19), and 2,6-di-O-acetyl-3,4-di-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (28) as the key synthons. Condensation of 6 with 7 gave the disaccharide donor 8, and subsequent condensation of 8 with 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->6)-2-O-acetyl-3,4-di-O-benzoyl-beta-D-galactopyranoside (9) followed by selective deacetylation afforded the tetrasaccharide acceptor 11. Coupling of 11 with 12 gave the pentasaccharide 13, its deallylation followed by coupling with 12, and debenzoylation gave the hexasaccharide 16 with beta-(1-->6)-linked galactopyranose backbone and 2- and 3'-linked alpha-L-arabinofuranose side chains. The octasaccharide 27 was similarly synthesized, while the twentyoside 42 was synthesized with tetrasaccharides 33 or 24 as the donors and 23, 36, 38, and 40 as the acceptors by consecutive couplings followed by deacylation.     

Syntheses of beta-(1-->6)-branched beta-(1-->3)-linked d-galactans that exist in the rhizomes of Atractylodes lancea DC

Effective syntheses of galactose hepta-, octa-, nona-, and decasaccharides that exist in the rhizomes of Atractylodes lancea DC were achieved with 2,3,4,6-tetra-O-benzoyl-alpha-d-galactopyranosyl trichloroacetimidate (1), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-d-galactopyranoside (2), 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-d-galactopyranosyl trichloroacetimidate (5), 4-methoxyphenyl 6-O-acetyl-2,4-di-O-benzoyl-beta-d-galactopyranoside (22), and 4-methoxyphenyl 2,4,6-tri-O-benzoyl-beta-d-galactopyranoside (26) as the key synthons. Coupling of 2 with 1, followed by oxidative cleavage of 1-OMP and subsequent trichloroacetimidate formation gave the beta-(1-->6)-linked disaccharide donor 4. Condensation of 2 with 5 and subsequent selective deacetylation by methanolysis produced the beta-(1-->6)-linked disaccharide acceptor 7. Reaction of 7 with 4, oxidative cleavage of 1-OMP, and trichloroacetimidate formation produced the tetrasaccharide donor 9. The penta- (15), the hexa- (17), and the heptasaccharide donor 19 were synthesized similarly. Meanwhile, treatment of 1 with 22 yielded beta-(1-->3)-linked disaccharide 23 and alpha-(1-->3)-linked disaccharide 25. Oxidative cleavage of 1-OMp of 23 followed by trichloroacetimidate formation produced the disaccharide donor 24. Coupling of 26 with 24, again, gave beta-linked 27 and alpha-linked 29. Selective 6-O-deacetylation of 27 afforded the trisaccharide acceptor 28. TMSOTf-promoted condensation 28 of with the tetra- (9), penta- (15), hexa-(17), and heptasaccharide donor 19, followed by deprotection, gave the target compounds.     

An efficient and concise synthesis of a beta-(1-->6)-linked D-galactofuranosyl hexasaccharide

A beta-(1-->6)-linked D-galactofuranosyl hexasaccharide was synthesized efficiently in a block construction manner by the well-known Schmidt glycosylation method using 6-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-galactofuranosyl trichloroacetimidate (1) and allyl 2,3,5-tri-O-benzoyl-beta-D-galactofuranoside (3) as the key synthons. Coupling of 3 with 1 gave beta-(1-->6)-linked disaccharide 4. Subsequent selective deacetylation of 4 afforded the disaccharide acceptor 5, while deallylation of 4 followed by trichloroacetimidate formation produced the disaccharide donor 6. Condensation of 5 with 6 gave the tetrasaccharide 7, and subsequent deacetylation afforded the tetrasaccharide acceptor 8. Finally, coupling of 8 with 6 followed by deacylation yielded the target beta-(1-->6)-linked galactofuranose hexasaccharide 10. All of the reactions in the synthesis were carried out smoothly and in high yield.     

alpha-D-Glcp-(1<-->1)-beta-D-Galp-containing oligosaccharides, novel products from lactose by the action of beta-galactosidase

A mixture of oligosaccharides produced by beta-galactosidase using lactose as a substrate was fractionated according to degree of polymerization using gel filtration, followed by high-pH anion-exchange chromatography. The fractions obtained were analyzed using monosaccharide analysis, methylation analysis, mass spectrometry, and NMR spectroscopy. Twelve novel non-reducing oligosaccharides were characterized, namely, [beta-D-Galp-(1-->4)]n-alpha-D-Glcp- (1<-->1)-beta-D-Galp[-(4<--1)-beta-D-Galp]m, with n, m = (1, 2, 3, or 4) and beta-D-Galp-(1-->2)-alpha-D-Glcp- (1<-->1)-beta-D-Galp.     

Synthesis of the O-linked pentasaccharide in glycoproteins of Trypanosoma cruzi and selective sialylation by recombinant trans-sialidase

The mucin-like glycoproteins of Trypanosoma cruzi have novel O-linked oligosaccharides that are acceptors of sialic acid in the trans-sialidase (TcTS) reaction. The transference of sialic acid from host glycoconjugates to the mucins is involved in infection and pathogenesis. The synthesis of the pentasaccharide, beta-D-Galp-(1-->2)-[beta-D-Galp-(1-->3)]-beta-D-Galp-(1-->6)-[beta-D-Galf-(1-->4)]-D-GlcpNAc and the corresponding alditol, previously isolated by reductive beta-elimination of the mucins, is described. The key step was the 6-O-glycosylation of a easily accessible derivative of beta-D-Galf-(1-->4)-D-GlcpNAc with a beta-D-Galp-(1-->2)-[beta-D-Galp-(1-->3)]-D-Galp donor using the trichloroacetimidate method. The beta-linkage was diastereoselectively obtained by the nitrile effect. The pentasaccharide is the major oligosaccharide in the mucins of T. cruzi, G strain and presents two terminal beta-D-Galp residues for possible sialylation by TcTS. A preparative sialylation reaction was performed with its benzyl glycoside and the sialylated product was isolated and characterized. NMR spectroscopic analysis showed that selective monosialylation occurred at the terminal (1-->3) linked galactopyranose.     

Synthesis of a hexasaccharide,the repeating unit of O-deacetylated GXM of C. neoformans serotype A

beta-D-GlcpA-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)[-beta-D-Xylp-(1-->2)]-alpha-D-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A, was synthesized as its allyl glycoside. Thus, 3-O-selective acetylation of allyl 4,6-O-benzylidene-alpha-D-mannopyranoside afforded 2, and subsequent glycosylation of 2 with 2,3,4-tri-O-benzoyl-D-xylopyranosyl trichloroacetimidate furnished the beta-(1-->2)-linked disaccharide 4. Debenzylidenation followed by benzoylation gave allyl 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-3-O-acetyl-4,6-di-O-benzoyl-alpha-D-mannopyranoside (5), and selective 3-O-deacetylation gave the disaccharide acceptor 6. Coupling of 6 with 2-O-acetyl-3,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate yielded the trisaccharide 8, and subsequent deallylation and trichloroacetimidation gave 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-[2-O-acetyl-3,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->3)]-4,6-di-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate (9). Condensation of the trisaccharide donor 9 with the disaccharide acceptor 6 gave the pentasaccharide 10 whose 2-O-deacetylation gave the acceptor 11. Glycosylation of 11 with methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate trichloroacetimidate and subsequent deprotection gave the target hexasaccharide.     

Synthesis of beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->2)-[beta-L-Xylp-(1-->4)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap,the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942

An efficient synthesis of beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->2)-[beta-L-Xylp-(1-->4)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap, the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942 and its isomer beta-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->4)-[beta-L-Xylp-(1-->2)]-alpha-L-Rhap-(1-->3)-alpha-L-Rhap was achieved via sequential assembly of the building blocks, allyl 2,3-O-isopropylidene-alpha-L-rhamnopyranoside (2), allyl 3,4-O-isopropylidene-alpha-L-rhamnopyranoside (3), allyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (6), 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate (7), and 2,3,4-tri-O-benzoyl-beta-L-xylopyranosyl trichloroacetimidate (12). The process was carried out in a regio- and stereoselective manner using glycosyl trichloroacetimidates as donors and unprotected or partially protected rhamnopyranosides as acceptors in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf).     

Synthesis of an xylosylated rhamnose pentasaccharide, the repeating unit of the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. begoniae GSPB 525

A xylosylated rhamnose pentasaccharide, alpha-L-Rhap-(1-->3)-[beta-L-Xylp-(1-->2)-]-alpha-L-Rhap-(1-->3)-[beta-L-Xylp-(1-->4)]-L-Rhap, the repeating unit of the O-chain polysaccharide (OPS) of the lipopolysaccharides of Xanthomonas campestris pv. begoniae GSPB 525 was synthesized by a highly regio- and stereoselective way. Thus coupling of 1,2-O-ethylidene-beta-L-rhamnopyranose (1) with 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (2) to give (1-->3)-linked disaccharide (3), subsequent benzoylation, deethylidenation, acetylation, 1-O-deacetylation, and trichloroacetimidation afforded the disaccharide donor 11. Condensation of 11 with 1 yielded 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-2-O-acetyl-4-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-1,2-O-ethylidene-beta-L-rhamnopyranose (12), and selective deacetylation of 12 yielded the trisaccharide diol acceptor 15. Coupling of 15 with 2,3,4-tri-O-benzoyl-alpha-L-xylopyranosyl trichloroacetimidate (16), followed by deprotection, gave the target pentasaccharide 19.     

Synthesis of divalent beta-(1-->6)-branched (1-->3)-glucohexaose and trivalent beta-(1-->6)-branched (1-->3)-glucotriose

Hexaose, beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-alpha-D-Glcp-(1-->3)-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp, based dimers were synthesized by twofold glycosidation of the hexaosyl trichloroacetimidate with hexylene 1,6-diol, diethylene glycol and triethylene glycol, respectively. Meanwhile, a triose, beta-1D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp, based trimer was obtained by glycosidation of the triosyl trichloroacetimidate with a glycerol-derived triol scaffold.     

Synthesis of two isomeric pentasaccharides,the possible repeating unit of the beta-glucan from the micro fungus Epicoccum nigrum Ehrenb. ex Schlecht

Two isomeric pentasaccharides, beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp (I) and beta-D-Glcp-(1-->6)-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->3)-beta-D-Glcp-(1-->6)]-beta-D-Glcp (II), the possible repeating unit of the beta-glucan from the micro fungus Epicoccum nigrum Ehrenb. ex Schlecht, were synthesized as their 4-methoxyphenyl glycosides in a regio- and stereoselective manner. The pentasaccharide I was obtained from 3-O-selective glycosylation of 4-methoxyphenyl 4,6-O-benzylidene-beta-D-glucopyranoside (12) with 2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (6) followed by acetylation, debenzylidenation, and 6-O-selective glucosylation with 2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl trichloroacetimidate (1), and then by deprotection. The pentasaccharide II was obtained from 3-O-selective coupling of 12 with 2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)-2,4-di-O-acetyl-3-O-allyl-alpha-D-glucopyranosyl trichloroacetimidate (10) followed by acetylation, debenzylidenation, and 6-O-selective glycosylation with 2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->3)-2,4,6-tri-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (11), and finally by deprotection.     

Synthesis of alpha-Manp-(1-->2)-alpha-Manp-(1-->3)-alpha-Manp-(1-->3)-Manp, the tetrasaccharide repeating unit of Escherichia coli O9a, and alpha-Manp-(1-->2)-alpha-Manp-(1-->2)-alpha-Manp-(1-->3)-alpha-Manp-(1-->3)-Manp, the pentasaccharide repeating unit of E. coli O9 and Klebsiella O3

The tetrasaccharide repeating unit of Escherichia coli O9a, alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->3)-alpha-D-Manp-(1-->3)-D-Manp, and the pentasaccharide repeating unit of E. coli O9 and Klebsiella O3, alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->3)-alpha-D-Manp-(1-->3)-D-Manp, were synthesized as their methyl glycosides. Thus, selective 3-O-allylation of p-methoxyphenyl alpha-D-mannopyranoside via a dibutyltin intermediate gave p-methoxyphenyl 3-O-allyl-alpha-D-mannopyranoside (2) in good yield. Benzoylation (-->3), then removal of 1-O-methoxyphenyl (right arrow4), and subsequent trichloroacetimidation afforded the 3-O-allyl-2,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate (5). Condensation of 5 with methyl 4,6-O-benzylidene-alpha-D-mannopyranoside (6) selectively afforded the (1-->3)-linked disaccharide 7. Benzoylation of 7, debenzylidenation, benzoylation, and deallylation gave methyl 2,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->3)-2,4,6-tri-O-benzoyl-alpha-D-mannopyranoside (11) as the disaccharide acceptor. Coupling of 11 with (1-->2)-linked mannose disaccharide donor 17 or trisaccharide donor 21, followed by deacylation, furnished the target tetrasaccharide and pentasaccharide, respectively.     

A facile and effective synthesis of alpha-(1-->6)-linked mannose di-, tri-, tetra-, hexa-, octa-, and dodecasaccharides, and beta-(1-->6)-linked glucose di-, tri-, tetra-, hexa-, and octasaccharides using sugar trichloroacetimidates as the donors and unprotected or partially protected glycosides as the acceptors

Reaction of 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl trichloroimidate with allyl alpha-D-mannopyranoside in the presence of TMSOTf selectively gave allyl 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-(1-->6)-alpha-D-mannopyranoside through an orthoester intermediate. Benzoylation of 3, followed by deallylation, and then trichloroimidation afforded the disaccharide donor 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroimidate, while benzoylation of 3 followed by selective removal of acetyl groups yielded the disaccharide acceptor allyl alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranoside. Coupling of 5 with 6 gave the tetrasaccharide allyl 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranoside, which were converted into the tetrasaccharide donor 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroimdate and the tetrasaccharide acceptor allyl alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranoside, respectively, by the same strategies as used for conversion of 3 into 5 and 6. Condensation of 5 with 13 gave the hexasaccharide 14, while condensation of 12 with 13 gave the octasaccharide 17. Dodecasaccharide 21 was obtained by the coupling of 12 with the octasaccharide acceptor 20. Similar strategies were used for the syntheses of beta-(1-->6)-linked glucose di-, tri-, tetra-, hexa-, and octamers. Deprotection of the oligosaccharides in ammonia-saturated methanol yielded the free alpha-(1-->6)-linked mannosyl and beta-(1-->6)-linked glucosyl oligomers.     

Elongation of both branches of biantennary backbones of oligo-(N-acetyllactosamino)glycans by human serum (1----3)-N-acetyl-beta-D- glucosaminyltransferase.

Partial reactions catalyzed by a (1----3)-N-acetyl-beta-D- glucosaminyltransferase (EC2.4.1.149), known to be present in human serum, were studied by use of biantennary "backbone" saccharides of oligo-N-acetyllactosamine-type as acceptors. Incubation of the radiolabeled blood-group I-active hexasaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-Galp- (1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Galp-(1----4)-D-GlcNAc (1) and UDP-GlcNAc with serum gave first a transient 1:1 mixture of two isomeric heptasaccharides, beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D- GlcpNAc-(1----3)-[beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D- Galp-(1----4)-D-GlcNAc (2) and beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-GlcpNAc-(1----3)- beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Galp-(1----4)-D-Glc NAc (3), showing that both branches of 1 react equally well. The two heptasaccharides reacted further in the incubation mixture to form the radiolabeled octasaccharide, beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[be ta-D- GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)]-beta-D-Ga lp- (1----4)-D-GlcNAc (4); during this second reaction, the composition of the heptasaccharide mixture remained unchanged, indicating that 2 and 3 reacted at approximately equal rates. The heptasaccharides 2 and 3 could not be separated from each other, but they could be detected, identified, and quantitatively determined by stepwise enzymic degradations. Partial (1----3)-N-acetyl-beta-D-glucosaminylation reactions, carried out with another acceptor, the branched pentasaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-[beta-D-Galp-(1----4)-beta- D- GlcpNAc-(1----6)]-beta-D-Gal (11), revealed that it reacted also equally well at both branches.(ABSTRACT TRUNCATED AT 400 WORDS)     

Synthesis of mannose-containing analogues of (1-->6)-branched (1-->3)-glucohexaose

Coupling of the trisaccharide acceptor 2,4,6-tri-O-acetyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-5-O-acetyl-1,2-O-isopropylidene-alpha-D-glucofuranose (2) with the trisaccharide donor 2,3,4,6-tetra-O-benzoyl-alpha-D-annopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (1) gave an alpha-linked hexasaccharide 3, while coupling of 2 with the trisaccharide donor 2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (7) produced alpha- 8 and beta-linked 12 hexasaccharides in a ratio of 3:2. Deprotection of 3, 8, and 12 afforded the analogues of the immunomodulator beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-alpha-D-Glcp-(1-->3)-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-D-Glcp (A).     

A practical synthesis of beta-D-GlcA-(1-->3)-beta-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-D-Xyl,a part of the common linkage region of a glycosaminoglycan

A practical synthesis of beta-D-GlcA-(1-->3)-beta-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-beta-D-Xyl-(1-->OMe) was achieved by coupling of methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate trichloroacetimidate with a trisaccharide acceptor. The trisaccharide acceptor was obtained by condensation of 3-O-allyl-2,4,6-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->3)-2,4,6-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate with methyl 2,3-di-O-benzoyl-beta-D-xylopyranoside, followed by deallylation. The beta-(1-->3)-linked disaccharide was prepared readily with p-methoxyphenyl 3-O-allyl-2,4,6-tri-O-benzoyl-beta-D-galactopyranoside as the key synthon. The alpha-(1-->3)-linkage was formed in considerable amount with galactose mono- and disaccharide trichloroacetimidate donors with C-2 neighboring group participation.     

Synthesis of beta-(1-->6)-branched beta-(1-->3) glucohexaose and its analogues containing an alpha-(1-->3) linked bond with antitumor activity

A beta-(1-->6)-branched beta-(1-->3)-glucohexaose, present in many biologically active polysaccharides from traditionally herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, was synthesized as its lauryl glycoside 32, and its analogues 18, 20 and 33 containing an alpha-(1-->3) linked bond were synthesized. It is interesting to find that coupling of a 3,6-branched acylated trisaccharide trichloroacetimidate donor 9 with 3,6-branched acceptors 13 and 16 with 3'-OH gave the alpha-(1--> 3)-linked hexasaccharides 17 and 19, respectively, in spite of the presence of C-2 ester capable of neighboring group participation. However, coupling of 9 with 4-methoxyphenyl 4,6-O-benzylidene-beta-D-glucopyranoside (27) selectively gave beta-(1-->3)-linked tetrasaccharide 28. Simple chemical transformation of the tetrasaccharide 28 gave acylated tetrasaccharide trichloroacetimidate 29. Coupling of 29 with lauryl (1-->6)-linked disaccharide 26 with 3-OH gave beta-(1-->3)-linked hexasaccharide 30 as the major product. Bioassay showed that in combination with the chemotherapeutic agent cyclophospamide (CPA), the hexaose 18 at a dose of 0.5-1mg/kg substantially increased the inhibition of S(180) for CPA, but decreased the toxicity caused by CPA. Some of these oligosaccharides also inhibited U(14) noumenal tumor in mice effectively.     

Synthesis of galactose-containing analogues of (1-->6)-branched (1-->3)-glucohexaose and its lauryl glycoside

Coupling of the trisaccharide acceptor either 2,4,6-tri-O-acetyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-5-O-acetyl-1,2-O-isopropylidene-alpha-D-glucofuranose (13) or lauryl 2,4,6-tri-O-acetyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,5-di-O-acetyl-alpha-D-glucopyranoside (15) with the trisaccharide donor 2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-galactopyranosyl trichloroacetimidate (12) gave alpha-linked hexasaccharides 14 and 16, respectively, while coupling of either 13 or 15 with trisaccharide donor 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-galactopyranosyl trichloroacetimidate 17 did not afford any hexasaccarides. The analogues of the immunomodulator beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-alpha-D-Glcp-(1-->3)-beta-D-Glcp-beta-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp (1) was obtained by deprotection of 14 and 16.     

Chemo-enzymatic synthesis of tetra-, penta-, and hexasaccharide fragments of the capsular polysaccharide of Streptococcus pneumoniae type 14

The chemo-enzymatic synthesis is described of beta-D-Glcp-(1-->6)-[beta-D-Galp-(1-->4)]-beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->O(CH(2))(6)NH(2) (1), beta-D-Glcp-(1-->6)-[beta-D-Galp-(1-->4)]-beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->O(CH(2))(6)NH(2) (2), beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->O(CH(2))(6)NH(2) (3), and beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->6)-[beta-D-Galp-(1-->4)]-beta-D-GlcpNAc-(1-->O(CH(2))(6)NH(2) (4), representing fragments of the repeating unit of the Streptococcus pneumoniae serotype 14 capsular polysaccharide. Linear intermediate oligosaccharides 5-8 were synthesized via chemical synthesis, followed by enzymatic galactosylation using bovine milk beta-1,4-galactosyltransferase as a catalyst. The title oligosaccharides form suitable compounds for conjugation with carrier proteins, to be tested as potential vaccines in animal models.     

Synthesis of beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->6)]-beta-D-Glcp-(1-->3)-beta-D-Glcp-(1-->6)-[beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->3)]-beta-D-GlcpOLauryl, an oligosaccharide with anti-tumor activity

A concise and effective synthesis of lauryl heptasaccharide 17 was achieved from the key intermediates lauryl 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranosyl-(1-->3)-2,4-di-O-benzoyl-beta-D-glucopyranoside (10) and isopropyl 2,4,6-tri-O-acetyl-3-O-allyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,4-di-O-acetyl-beta-D-glucopyranosyl-(1-->3)-2,4,6-tri-O-acetyl-1-thio-beta-D-glucopyranoside (15). The key trisaccharide glycosyl acceptor 10 was constructed by coupling 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-benzoyl-alpha-D-glucopyranosyl trichloroacetimidate (3) with lauryl 6-O-acetyl-2,4-di-O-benzoyl-beta-D-glucopyranoside (9), followed by deacetylation. The thioglycoside donor 15 was obtained by condensation of 2,4,6-tri-O-acetyl-3-O-allyl-beta-D-glucopyranosyl-(1-->3)-[2,3,4,6-tetra-O-benzoyl-beta-D-glucopyranosyl-(1-->6)]-2,4-di-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (11) with isopropyl 4,6-O-benzylidene-1-thio-beta-D-glucopyranoside (12), followed by debenzylidenation and acetylation. A bioassay of the inhibition of S180 noumenal tumors showed that lauryl heptasaccharide 17 could be employed as a potential agent for cancer treatment.