SYNTHESIS OF NEW OXAMIDE DERIVATIVES OF D-GLUCOSAMINE AND ALIPHATIC OR AROMATIC AMINES

New oxamides, derivatives of D-glucosamine and aliphatic or aromatic amines were prepared by acylation of methyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-α- or -β-D-glucopyranoside (1c or 1d) with oxalyl chloride, followed by reaction with amine. The reaction was assumed to proceed by the intermediate of N-carbomethoxy N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α or β-D-glucopyranosid-2-yl) oxamic acid chloride which reacted with amines, and afforded N-acetyl, N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α- or -β-D-glucopyranosid-2-yl), N′-alkyl or aryloxamide (5–7), and N-(methyl 3,4,6-tri-O-acetyl-2-deoxy-α- or -β-D-glucopyranosid-2-yl), N′-alkyl or aryloxamide (8–13).     

Synthesis of 6-S-(5-Acetamido-3,5-Dideoxy-D-Glycero-α-D-Galacto-2-Nonulopyranosylonic Acid)-6-Thio-Hexopyranosides

The reaction of the sodium salt of methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-α-D-galacto-2-nonulo-pyranosonate with a variety of 6-bromo-6-deoxy-D-hexopyranosides, such as methyl 2,3,4-tri-O-acetyl-6-bromo-6-deoxy-α-D-glucopyranos-ide, -galactopyranoside, allyl 2,3,4-tri-O-acetyl-6-bromo-6-deoxy-β-D-glucopyranoside, and allyl 2-acetamido-3,4-di-O-acetyl-6-bromo-2,6-dideoxy-β-D-glucopyranoside, gave the corresponding (2→6)-linked disaccharides, α-glycosides of 2-thio-N-acetylneuraminic acid derivative in good yields. These disaccharides were converted, via O-deacetylation, followed by hydrolytic removal of the ester group, into the title compounds.     

Mimics of the Structural Elements of Type III Group B Streptococcus Capsular Polysaccharide. Part I: Synthesis of a Carboxylate-Containing Pentasaccharide

Abstract

A carboxylate-containing pentasaccharide, methyl O-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-β-d-galactopyranoside (27) was synthesized by block condensation of suitably protected donors and acceptors. Phenyl 3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (17) was condensed with methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (4) to afford a disaccharide, methyl O-(3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (18). Removal of chloroacetyl groups gave 4,6-diol, methyl 0-(3-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (19), in which the primary hydroxy group (6-OH) was then selectively chloroacetylated to give methyl O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (20). This acceptor was then coupled with 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (14) to afford a trisaccharide, methyl O-{2,4,6-tri-O-acetyl-3-O-[(S)-l-(methoxycarbonyl)ethyl]-β-d-galactopyranosyl}-(1→4)-O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (21). Removal of the 6-O-chloroacetyl group in 21 gave 22, which was coupled with 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (23) to yield protected pentasaccharide 24. Standard procedures were used to remove acetyl groups and the phthalimido group, followed by N-acetylation, and debenzylation to yield pentasaccharide 27 and a hydrazide by-product (28) in a 5:1 ratio, respectively. Compound 27 contains a complete repeating unit of the capsular polysaccharide of type III group B Streptococcus in which terminal sialic acid is replaced by an (S)-1-carboxyethyl group.     

SYNTHESIS OF SIALYL-α-(2→3)-NEOLACTOTETRAOSE DERIVATIVES MODIFIED AT C-2 OF THE N-ACETYLGLUCOSAMINE RESIDUE: PROBES FOR INVESTIGATION OF ACCEPTOR SPECIFICITY OF HUMAN α-1,3-FUCOSYLTRANSFERASES,FUC-TVII,AND FUC-TVI *

A variety of sialyl-α-(2→3)-neolactotetraose (IV³NeuAcnLcOse₄ or IV³NeuGcnLcOse₄) derivatives (23, 31–37, 58–60) modified at C-2 of the GlcNAc residue have been synthesized. The phthalimido group at C-2 of GlcNAc in 2-(trimethylsilyl)ethyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (5) was systematically converted to a series of acylamino groups, to give the per-O-benzylated trisaccharide acceptors (6–11). On the other hand, modification of the hydroxyl group at C-2 of the terminal Glc residue in 2-(trimethylsilyl)ethyl (4,6-O-benzylidene-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (42) gave three different kinds of trisaccharide acceptors containing D-glucose (49), N-acetyl-d-mannosamine (50), and D-mannose (51) instead of the GlcNAc residue. Totally ten trisaccharide acceptors (5–11 and 49–51) were each coupled with sialyl-α-(2→3)-galactose donor 12 to afford the corresponding pentasaccharides (14–21 and 52–54) in good yields, respectively, which were then transformed into the target compounds. Acceptor specificity of the synthetic sialyl-α-(2→3)-neolactotetraose probes for the human α-(1→3)-fucosyltransferases, Fuc-TVII and Fuc-TVI, was examined.     

Synthetic Studies on Sialoglycoconjugates 61: Synthesis of α-Series Ganglioside GM1α

Abstract

A stereocontrolled synthesis of α-series ganglioside GM1α (III⁶Neu5AcGgOse₄Cer) is described. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,3,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (1) with the suitably protected galactosamine donor, methyl 3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-1-thio-β-d-galactopyranoside (4) gave the desired trisaccharide, which was transformed into the trisaccharide acceptor via removal of the phthaloyl and O-acetyl groups followed by N-acetylation. Glycosylation of this acceptor with methyl 3-O-benzyl-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (7) gave the asialo GM1 saccharide derivative, which was transformed into the acceptor by removal of benzylidene group. Coupling of this gangliotetraose acceptor with phenyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-d-glcero-d-galacto-2-nonulopyranosyl)onate by use of NIS-TfOH afforded the desired GM1α oligosaccharide derivative in high yield, which was transformed, via removal of the benzyl group followed by O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and subsequent imidate formation, into the final glycosyl donor. Condensation of this imidate derivative with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15) gave the β-glycoside, which on channeling through selective reduction of azido group, coupling of the amino group with octadecanoic acid, O-deacylation and saponification of the methyl ester group, gave the title compound GM1α.     

SYNTHESIS OF THE C-DISACCHARIDE α-C(1→3)-L-FUCOPYRANOSIDE OF N-ACETYLGALACTOSAMINE[1]

Radical C-glycosidation of racemic 5-exo-benzeneselenyl-6-endo-chloro-3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one ((±)-2) with α-acetobromofucose (3) provided a mixture of α-C-fucosides that were reduced with NaBH₄ to give two diastereomeric alcohols that were separated readily. One of them ((?)-6) was converted into (?)-methyl 2-acetamido-4-O-acetyl-2,3-dideoxy-3-C-(3′,4′,5′-tri-O-acetyl-2′,6′-anhydro-1′,7′-dideoxy-α-L-glycero-D-galacto-heptitol-1′-C-yl)-α -D-galactopyranuronate ((?)-11) and then into (?)-methyl 2-acetamido-2,3-dideoxy-3-C-(2′,6′-anhydro-1′,7′-dideoxy-α-L-glycero-D-galacto-heptitol-1′-C-yl)-β -D-galactopyranoside ((?)-1), a new α-C(1→3)-L-fucopyranoside of N-acetylgalactosamine. Its ¹H NMR data shows that this C-disaccharide (α-L-Fucp-(1→3)CH₂-β-D-GalNAc-OMe) adopts a major conformation in solution similar to that expected for the corresponding O-linked disaccharide, i.e., with antiperiplanar σ(C-3′,C-2′) and σ(C-1′,C-3) bonds.     

Synthetic Studies on Sialoglycoconjugates 59: Total Synthesis of Tumor-Associated Ganglioside,Sialyl Le

Abstract

The first total synthesis of tumor-associated glycolipid antigen, sialyl Le^a, is described. Methylsulfenyl bromide-silver triflate-promoted coupling of 2-(trimethylsilyl)ethyl O-(2-acetamido-6-O-benzyl-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (2) with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (3) afforded the pentasaccharide 4a and 5a in good yields. Glycosylation of 4a with methyl 2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside (6) by use of N-iodosuccinimide (NIS) — trifluoromethanesulfonic acid (TfOH) as a promoter, gave the desired hexasaccharide 7. Compound 7 was converted into the α-trichloroacetimidate 10, via reductive removal of benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S, 3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1, 3-diol (11), gave the β-glycoside 12. Finally, 12 was transformed, via selective reduction of the azide group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 15 in good yield.     

Stereoselective Glycosidic Coupling Reactions of Fully Benzylated 1,2-Anhydro Sugars with N-Tosyl- or N-Benzyloxycarbonyl-l-serine Methyl Ester

Abstract

The glycosidic coupling reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose (7), 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-galactopyranose (21), and 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose (18) with N-tosyl- (10) or N-benzyloxycarbonyl- (11) L-serine methyl ester provides a new stereocontrolled synthesis of 1,2-trans linked glycopeptides. The 1,2-anhydro sugars are shown to react smoothyl with 10 or 11 in the presence of Lewis acid (ZnCl₂ or AgOTf) as well as powdered 4A molecular sieves in CH₂Cl₂ at room temperature to afford glycosyl serine derivatives with high stereoselectivity and high yield in less than 30 min. An improved method using 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-mannopyranosyl chloride (6) as the key intermediate for ring closure was applied for the synthesis of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose.     

Synthetic Studies on Sialoglycoconjugates 75: A Total Synthesis of β-Series Ganglioside GQ1β

Abstract

A first total synthesis of a β-series ganglioside GQ1β (IV³Neu5Acα2, III⁶Neu5Acα2-Gg4Cer) is described. Regio- and stereoselective dimeric sialylation of the hydroxyl group at C-6 of the GalNAc residue in 2-(trimethylsilyl)ethyl O-(2-acetamido-2-deoxy-3-O-levulinyl-β-d-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-O-2,3,6-tri-O-benzyl-β-d-glucopyranoside (3) 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-nonulopyranosylono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-2-thio-d-glycero-d-galacto-2-nonulopyranosid]onate (4) using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as a promoter gave the desired pentasaccharide 5 containing α-glycosidically-linked dimeric sialic acids. This was transformed into the acceptor 6 by removal of the levulinyl group. Condensation of methyl O-[methyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-d-glycero-d-galacto-2-nonulopyranosylonate]-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (7) with 6, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the desired octasaccharide derivative 8 in high yield. Compound 8 was converted into α-trichloroacetimidate 11, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (12), gave the β-glycoside 13. Finally, 13 was transformed, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 15 in good yield.     

SYNTHESIS OF A MANNOTETRAOSE—THE REPEATING UNIT OF THE CELL-WALL MANNANS OF MICROSPORUM GYPSEUM AND RELATED SPECIES OF TRYCHOPHYTON

A tetrasaccharide, α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-α-D-mannopyranosyl-(1→6)-D-mannopyranose (1), the repeating unit of the cell-wall mannans of Microsporum gypseum and related species of Trychophyton, was synthesized using 6-O-acetyl-2,3,4-tri-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (5) and 2-O-acetyl-3,4,6-tri-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (13) as the glycosyl donors in “the inverse Schmidt” procedure.     

Click synthesis of N1-(β-D-ribofuranosyl)-C4-(coumarin-4″-yl)-1,2,3-triazoles

A series of eight N¹-(β-D-ribofuranosyl)-C⁴-(coumarin-4′′-yl)-1,2,3-triazoles have been synthesized by Cu(I)-catalyzed click reaction of 1-azido-1-deoxy-2,3,5-tri-O-benzoyl-β-D-ribofuranose with differently substituted 4-ethynylcoumarins followed by debenzoylation of the resulted N¹-(2′,3′,5′-tri-O-benzoyl-β-D-ribofuranosyl)-C⁴-(coumarin-4″-yl)-1,2,3-triazoles in 71 to 89% overall yields. The structures of all the synthesized compounds were established on the basis of their spectral data analysis that was further confirmed by X-ray data analysis of one of the model benzoylated compounds, i.e. N¹-(2′,3′,5′-tri-O-benzoyl-β-D-ribofuranosyl)-C⁴-(7″-isopropoxycoumarin-4″-yl)-1,2,3-triazole.     

A FACILE SYNTHESIS OF MANNOSE TRI- AND TETRASACCHARIDE REPEATING UNITS OF FUNGAL CELL-WALL POLYSACCHARIDE FROM MICROSPORUM AND TRYCHOPHYTON SPECIES

ABSTRACT

A facile synthesis of the trisaccharide α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-α-D-mannopyranose and the tetrasaccharide α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→6)-α-D-mannopyranosyl-(1→6)-D-mannopyranose, the repeating units of fungal cell-wall polysaccharide from Microsporum gypseum and Trychophyton, was achieved using α-(1→2)-linked disaccharide imidate as the donor. The disaccharide imidate was prepared from the self-condensation of 3,4,6-tri-O-benzoyl-1,2-O-allyloxyethylidene-β-D-mannopyranose.     

NON-ANOMERIC SUGAR ISOUREAS

Six non-anomeric isourea derivatives of d-fructose (7, 8), d-glucose (9, 10), 6-deoxy-l-altrose (11) and l-rhamnose (12) were synthesized from the precursors 1–6 by a CuCl-catalyzed addition of a non-glycosidic OH-group to DCC and DIPC, respectively. Subsequently, the isoureido group of phenyl 2,3,4-tri-O-benzyl-6-O-(N,N′-dicyclohexylisoureido)-β-d-glucopyranoside (10) was replaced by an azido and a thioacetyl group, respectively, yielding the corresponding 6-deoxy-6-azido-d-glucopyranoside (13) and 6-deoxy-6-thioacetyl-d-glucopyranoside (14) in moderate to good yields.     

Synthetic Studies on Sialoglycoconjugates 66: First Total Synthesis of a Cholinergic Neuron-Specific Ganglioside GQ1bα1

Abstract

A first total synthesis of a cholinergic neuron-specific ganglioside, GQ1bα (IV³Neu5Acα, III⁶Neu5Acα, II³Neu5Acα₂-Gg₄Cer) is described. Regio- and stereo-selective monosialylation of the hydroxyl group at C-6 of the GalNAc residue in 2-(trimethylsilyl)ethyl O-(2-acetamido-2-deoxy-3,4-O-isopropylidene-β-d-galactopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-dgalactopyranosyl)-(1→4)- O-2,3,6-tri-O-benzyl-β-dglucopyranoside (4) with methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-d glycero-d galacto-2-nonulopyranosid) onate (5), and subsequent dimericsialylation of the hydroxyl group at C-3 of the Gal residue 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-nonulopyranosylono-1′,9-lactone)-4, 7-di-O-acetyl-3,5-dideoxy-2-thio-d glycero-d galacto-2-nonulopyranosid]onate (7), using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as a promoter, gave the desired hexasaccharide 8 containing α-glycosidically-linked mono- and dimeric sialic acids. This was transformed into the acceptor 9 by removal of the isopropylidene group. Condensation of methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d glycero-α-d galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-dgalactopyranoside (10) with 9, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the desired octasaccharide derivative 11 in high yield. Compound 11 was converted into α-trichloroacetimidate 14, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15), gave the β-glycoside 16. Finally, 16 was transformed, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 18 in good yield.     

Synthesis of Methyl α-d-Allopyranoside and Methyl α-d-Ribo-hexopyranoside: A Convenient Chemoenzymatic Approach

Abstract

An efficient chemoenzymatic synthesis of methyl α-d-allopyranoside and methyl 3-deoxy-α-d-ribo-hexopyranoside starting from methyl 4,6-O-benzylidene-α-d-glucopyranoside is described.     

Synthetic Studies on Sialoglycoconjugates 70: Synthesis of Sialyl and Sulfo Lewis × Analogs Containing a Ceramide or 2-(Tetradecyl)hexadecyl Residue

Abstract

Four sialyl and sulfo Le^x analogs containing glucose in place of N-acetylglucosamine, and a ceramide or 2-(tetradecyl)hexadecyl residue, have been synthesized. Condensation of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-O-(4-O-acetyl-2,6-diO-benzoyl-β-d-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-acetyl-α-L-fucopyranosyl)-(1→3)]-2,4-di-O-benzoyl-α-d-glucopyranosyl trichloroacetimidate (1) with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3, diol (2) or 2-(tetradecyl)-hexadecyl-1-ol (3) gave the corresponding β-glycosides 4 and 7. Compound 4 was converted into the ganglioside 6 via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and saponification of the methyl ester group. Hydrolysis of the O-acyl groups in 7 followed by saponification of the methyl ester, gave sialyl Le^x ganglioside analog 8 containing a branched fatty alkyl residue. On the other hand, glycosylation of O-(4-O-acetyl-2,6-di-O-benzoyl-3-O-levulinyl-β-d-galactopyranosyl)-(1→4)-[O-(2,3,4-tri-O-acetyl-α-L-fucopyranosyl)-(1→3)]-2,6-di-O-benzoyl-α-d-glucopyranosyl trichloroacetimidate (13), prepared from 2-(trimethylsilyl)ethyl O-(2,6-di-O-benzoyl-β-d-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)]-2,6-di-O-benzoyl-β-d-glucopyranoside (9) via selective 3-O-levulinylation, acetylation, removal of the 2-(trimethylsilyl)ethyl group, with 2 or 3, gave the desired β-glycosides 14 and 19. Selective reduction of the axido group in 14 followed by coupling with octadecanoic acid gave the ceramide derivative 16. Removal of the levulinyl group in 16 and 19, treatment with sulfur trioxide pyridine complex and subsequent hydrolysis of the protecting groups yielded the corresponding sulfo Le^x analogs 18 and 21.     

SYNTHESIS,NMR, AND CONFORMATIONAL STUDIES OF FUCOIDAN FRAGMENTS 4[1]: 4-MONO- AND 4,4′-DISULFATED (1→3)-α-l-FUCOBIOSIDE AND 4-SULFATED FUCOSIDE FRAGMENTS

Propyl 4-O-sulfonato- and 4,4′-di-O-sulfonato-3-O-α-l-fucopyranosyl-α-l-fucopyranosides, which are related to fragments of brown algal fucoidans, have been synthesized. Their spectral (¹H and ¹³C NMR, NOE) and conformational properties have been studied in combination with molecular modeling and compared with the respective non-sulfated propyl fucobioside. Correlations between chemical shifts and conformational properties of these compounds were investigated.     

Two new quercetin glycoside derivatives from the fruits of Gardenia jasminoides var. radicans

Two new quercetin glycoside derivatives named quercetin-3-O-[2-O-trans-caffeoyl-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside] (1) and quercetin-3-O-[2-O-trans-caffeoyl-β-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside] (2) along with three known flavonoids, 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone (3), 5,7-dihydroxy-8-methoxyflavone (4) and kaempferol 3-O-β-d-glucopyranoside (5), were isolated from the fruits of Gardenia jasminoides var. radicans. The structures of the new compounds were determined by means of extensive spectroscopic analysis (1D, 2D NMR and HR-ESI-MS), glycoside hydrolysis and sugar HPLC analysis after derivatisation. This is the first report on the isolation of a pair of compounds with α or β-l-rhamnopyranosyl configuration from plant and the first detail assignment of their NMR data.     

A new triterpenoid glycoside from the leaves and stems of Duranta repens

A new triterpenoid glycoside (1) was isolated from the methanol extract of the leaves and stems of Duranta repens L. (Verbenaceae) along with 14 known compounds consisting of eight triterpenoids, four iridoids, one phenylethanoid glycoside and one flavonoid. The chemical structure of 1 was determined to be bayogenin 3-O-[β-D-glucopyranoside]-28-O-[α-L-rhamnopyranosyl-(1→5)-O-β-D-apiofuranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl] ester, based on spectroscopic data. In addition, the inhibitory effects of the isolates on lipoxygenase activity were examined. Among them, acteoside and apigenin resulted in 94 ± 3.6% and 82 ± 4.7% inhibition, respectively, at 0.5 mM.     

Preparation of Anhydro-Thiohexofuranosides from Methyl Fructofuranosides Via the Thio-Mitsunobu Reaction 1

Abstract

Methyl α-D-fructofuranoside was transformed regioselectively into the corresponding 6-S-thioacetate in one step by use of the thio-Mitsunobu reaction. Reaction of the trimesylate derived from this thioacetate with sodium hydrogen carbonate led to the thietanosugar methyl 4,6-anhydro-1,3-di-O-mesyl-4-thio-α-D-tagatofuranoside. Methyl β-D-fructofuranoside gave the corresponding 6-S-thioacetate and, with excess thioacetic acid, the 1-S,6-S-bis-thioacetate. Whereas this mono-thioacetate did not yield a thietano derivative, the bis-thioacetate gave the bis-thietane methyl 1,3:4,6-dianhydro-1,4-dithio-β-D-sorbofuranoside with sodium hydrogen carbonate.