Isolation,structural elucidation and cytotoxicity evaluation of a new pentahydroxy-pimarane diterpenoid along with other chemical constituents from Aerva lanata

Aervalanata possesses various useful medicinal and pharmaceutical activities. Phytochemical investigation of the plant has now led to the isolation of a new 2α,3α,15,16,19-pentahydroxy pimar-8(14)-ene diterpenoid (1) together with 12 other known compounds identified as β-sitosterol (2), β-sitosterol-3-O-β-D-glucoside (3), canthin-6-one (4), 10-hydroxycanthin-6-one (aervine, 5), 10-methoxycanthin-6-one (methylaervine, 6), β-carboline-1-propionic acid (7), 1-O-β-D-glucopyranosyl-(2S,3R,8E)-2-[(2′R)-2-hydroxylpalmitoylamino]-8-octadecene-1,3-diol (8), 1-O-(β-D-glucopyranosyl)-(2S,3S,4R,8Z)-2-[(2′R)-2′-hydroxytetracosanoylamino]-8(Z)-octadene-1,3,4-triol (9), (2S,3S,4R,10E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-10-octadecene-1,3,4-triol (10), 6′-O-(4″-hydroxy-trans-cinnamoyl)-kaempferol-3-O-β-D-glucopyranoside (tribuloside, 11), 3-cinnamoyltribuloside (12) and sulfonoquinovosyldiacylglyceride (13). Among these, six compounds (8–13) are reported for the first time from this plant. Cytotoxicity evaluation of the compounds against five cancer cell lines (CHO, HepG2, HeLa, A-431 and MCF-7) shows promising IC₅₀ values for compounds 4, 6 and 12.     

THE SYNTHESIS OF SOME C-4 AND C-9 SUBSTITUTED DERIVATIVES OF KDN2EN METHYL ESTER

The synthesis of a number of C-4 and C-9 substituted derivatives of KDN2en methyl ester 2 is reported. 9-Deoxy-9-iodo, 9-azido-9-deoxy and 9-O-methyl derivatives of 2(compounds 5, 7and 9) were prepared from the corresponding 9-O-tosylate, methyl 2,6-anhydro-3-deoxy-9-O-p-toluenesulfonyl-D-glycero-D-galacto-non-2-enonate (3). These compounds have been fully characterised as the peracetates 6, 8 and 10. Treatment of 3 with KSAc gave the 9-thioacetyl derivative which was isolated as the peracetate 11. 4-C-Ethenyl-4-deoxy (14), 4-C-phenyl-4-deoxy (15) and 4-C-[1-(methoxycarbonyl)ethenyl]-4-deoxy (16) derivatives of 2were prepared via the palladium-catalysed coupling of the 4-epi-chloride, methyl 5,7,8,9-tetra-O-acetyl-2,6-anhydro-4-chloro-3,4-dideoxy-D-glycero-D-talo-non-2-enonate (12) with the appropriate organostannanes.     

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.     

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.     

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.     

SYNTHESIS OF 3-O-ARABINOSYLATED (1→6)-β-D-GALACTAN EPITOPES

Two tetrameric arabinogalactans, β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-[α-L-arabinofuranosyl-(1→3)]-D-galactopyranose (14) and α-L-arabinofuranosyl-(1→3)-β-D-galactopyranosyl-(1→6)-β-D-galactopyranosyl-(1→6)-D-galactopyranose (25), which are good candidates for CCRC-M7 epitope characterization, were synthesized efficiently using a convergent strategy. Migration of an acceptor acetyl group proved to be an obstacle to synthesis, but regioselective glycosylation or 4-O-benzyl protection of the acceptor circumvented this problem allowing efficient synthesis of the 1→6 linked target compounds.     

SYNTHESIS OF (2,3,4,6-TETRA-O-ACETYL-α-D-GLYCOPYRANOSYL) THIOPHENE DERIVATIVES AS NEW C-NUCLEOSIDE ANALOGUES[1]

Treatment of 2-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)ethanal (1a) and 2-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)ethanal (1b) respectively with malononitrile in the presence of silica gel provided the corresponding 4-[2,3,4,6-tetra-O-acetyl-α-D-glycopyranosyl]-2-cyanocrotononitriles (2a) and (2b). Starting from 2a and 2b, respectively, cyclizations with sulfur and triethylamine yielded 5-[2,3,4,6-tetra-O-acetyl-α-D-glycopyranosyl]-2-aminothiophene-3-carbonitriles (3a) and (3b). Further cyclizations could be achieved by utilizing of triethyl orthoformate/ammonia to furnish the 6-(α-D-glycopyranosyl)thieno[2,3-d]pyrimidine-4-amines 4a and 4b.     

New flavonoid glycosides and other chemical constituents from Clerodendrum phlomidis leaves: isolation and characterisation

Phytochemical investigation of the plant Clerodendrum phlomidis Linn. F. (Lamiaceae) has now led to the isolation of two new flavonoid glycosides (1, 2) together with six known compounds identified as pectolinaringenin (3), pectolinaringenin-7-O-β-d-glucopyranoside (4), 24β-ethylcholesta-5,22E,25-triene-3β-ol (5), 24β-ethylcholesta-5,22E,25-triene-3β-O-β-D-glucopyranoside (6), (2S,3S,4R,10E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-10-octadecene-1,3,4-triol (7) and andrographolide (8) mainly by spectroscopic analysis. Compounds 4 and 6–8 are reported for the first time from C. phlomidis.     

A new triterpenoid saponin from Clinopodium chinense (Benth.) O. Kuntze

A new triterpene saponin, 3β,16β,23α,28β,30β-pentahydroxyl-olean-11,13(18)-dien-3β-yl-[β-d-glucopyranosyl-(1→2)]-[β-d-glucopyranosyl-(1→3)]-β-d-fucopyranoside, was named Clinoposaponin D (1), together with six known triterpene saponins, buddlejasaponin IVb (2), buddlejasaponin IVa (3), buddlejasaponin IV (4), clinopodisides D (5), 11α,16β,23,28-Tetrahydroxyolean-12-en-3β-yl-[β-d-glucopyranosyl-(1→2)]-[β-d-glucopyranosyl-(1→3)]-β-d-fucopyranoside (6) and prosaikogenin A (7), and two known triterpenes, saikogenin A (8) and saikogenin F (9) were isolated from Clinopodium chinense (Benth.) O. Kuntze. Their structures were elucidated on the basis of 1D, 2D NMR and MS analysis. Meanwhile, the effects of all compounds on rabbit platelet aggregation and thrombin time (TT) were investigated in vitro. Compounds 4 and 7 had significant promoting effects on platelet aggregation with EC₅₀ value at 53.4 and 12.2 μM, respectively. In addition, the highest concentration (200 μM) of compounds 2 and 9 shortened TT by 20.6 and 25.1%, respectively.     

Cytotoxic flavonoids and other constituents from the stem bark of Ochna schweinfurthiana

Seven flavonoids, hemerocallone (1), 6,7-dimethoxy-3′,4′-dimethoxyisoflavone (2), amentoflavone (4), agathisflavone (6), cupressuflavone (8), robustaflavone (9) and epicatechin (10), together with three other compounds, lithospermoside (3), β-D-fructofuranosyl-α-D-glucopyranoside (5) and 3β-O-D-glucopyranosyl-β-stigmasterol (7), were isolated from the ethyl acetate extract of the stem bark of Ochna schweinfurthiana F. Hoffm. All the compounds were characterised by spectroscopic and mass spectrometric methods, and by comparison with literature data. Cytotoxicity of the extracts and compounds against cervical adenocarcinoma (HeLa) cells was evaluated by MTT assay. Compounds 4 and 6 exhibited good cytotoxic activity, with IC₅₀ values of 20.7 and 10.0 μM, respectively.     

SYNTHESIS OF ANELLATED ANHYDROPYRANOSES ON THE BASIS OF 1,6-ANHYDRO-3-DEOXY-4-METHYLSULFANYL-3-[(METHYLSULFANYL)METHYLENE]-β-D-ERYTHRO-HEXOPYRANOS-2-ULOSE

(Z)-1,6-Anhydro-3-deoxy-4-methylsulfanyl-3-[(methylsulfanyl)methylene]-β-D-erythro-hexopyranos-2-ulose (1) reacted with diethyl malonate, 1,3-diketones, N-aryl-3-oxobutyramides and dialkyl 3-oxoglutarate, respectively, in the presence of potassium carbonate and crown ether to yield diethyl 2-(1,6-anhydro-4-methylsulfanyl—D-arabino-hex-2-ulopyranos-3-ylmethylene) malonate (2), 1-{(1R,2S,8S,9R)-2-hydroxy-4-methyl-8-methylthio-3,11,12- trioxatricyclo7.2.1.0^2,7dodeca-4,6-dien-5-yl} ethanone (3), (1R,2S,12S,13R)-2-hydroxy-12-methylthio-3,15,16-trioxatetracyclo[11.2.1. 0^2,11. 0^4,9] hexadeca- 4(9),10-dien-8-one (4), (1R,8S,9R)-5-acetyl-3-aryl-8-methylthio-11,12-dioxa- 3-azatricyclo-[7.2.1.0^2,7]dodeca-2(7),5-dien-4-ones (5,6) and dialkyl (1R,8S,-9R)-4-hydroxy-8-methylthio-11,12-dioxatricyclo[7.2.1.0^2,7]dodeca-2(7),3,5-triene-3,5-dicarboxylates (7,8), respectively.     

BLOCK SYNTHESIS WITH GALACTURONATE TRICHLOROACETIMIDATES[1]

The disaccharide methyl (4-O-benzoyl-3-O-benzyl-2-O-acetyl-α-L-rhamno pyranosyl)-(1→4)-(allyl 2,3-di-O-benzyl-β-D-galactopyranosid)uronate (13) was obtained in an excellent yield of 88% using methyl (allyl 2,3-di-O-benzyl-β-D-galactopyranosid)uronate ((12) as the glycosyl acceptor and a slight excess of the 1,2-di-O-acetyl-rhamnoglycosyl donor 5a. Disaccharide 13 is a key intermediate that can be used either as a glycosyl acceptor or glycosyl donor for the preparation of rhamnogalacturonan fragments. Here, introduction of the trichloroacetimidate function at the anomeric center gave the disaccharide glycosyl donor 28, which could be applied in a blockwise glycosylation reaction to form the L-Rha-α(1→4)-D-GalA-α(1→4)-D-GalA trisaccharide 29. Generally, on condition that no neighboring group effect influenced the reaction at the anomeric center of the α-trichloroacetimidate galacturonate glycosyl donors (20–22, 28), α-glycosidic linkages were nearly exclusively formed, except in the case of the 4-O-methylgalactopyranosyluronate 22.     

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.     

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.     

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 β-d-Glcp-(1→2)-[β-d-Ribf-(1→3)-]α-l-Rhap-(1→3)-α-l-Rhap-(1→2)-α-l-Rhap,THE REPEATING UNIT OF THE LIPOPOLYSACCHARIDE OF Acetobacter diazotrophicus PAL 5

A pentasaccharide, the major repeating unit of the lipopolysaccharide (LPS) of the nitrogen fixing bacterium Acetobacter diazotrophicus PAL 5 was efficiently synthesized as its allyl glycoside using a regio- and stereo-selective strategy. The key acceptor, allyl 3-O-acetyl-4-O-benzoyl-α-l-rhamnopyranoside (3), was prepared by selective 3-O-acetylation of allyl 4-O-benzoyl-α-l-rhamnopyranoside. Condensation of 3 with 2,3,4,6-tetra-O-benzoyl-α-d-glucopyranosyl trichloroacetimidate furnished the disaccharide 5. Deallylation and subsequent trichloroacetimidation of 5 afforded 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→2)-3-O-acetyl-4-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (10). Selective 3-O-glycosylation of allyl α-l-rhamnopyranoside (1) with 10 followed by benzoylation gave trisaccharide (12), which could be conveniently converted to a donor (14). Condensation of 14 with allyl 3,4-di-O-benzoyl-α-l-rhamnopyranoside (15) gave tetrasaccharide 16. Selective deacetylation of 16 gave the acceptor 17 which was ribosylated to furnish the protected pentasaccharide, and finally deprotection led to the title compound.     

Synthesis of 4-Octuloses from a Derivative of d-Fructose

Abstract

Reaction of 2,3:4,5-di-O-isopropylidene-β-d-arabino--hexos-2-ulo-2,6-pyranose (1) with (methoxycarbonylmethylene)triphenylphosphorane in either dichloromethane or methanol gave methyl (E)-2,3-dideoxy-4,5:6,7-di-O-isopropylidene-β-d-arabino-oct-2-ene-4-ulo-4,8-pyranosonate (2) or a 1:2.3 mixture of 2 and its Z-isomer (3), respectively. Bishydroxylation of 2 with osmium tetraoxide gave a mixture of methyl 4,5:6,7-di-O-isopropylidene-β-d-glycero-d-galacto- (4) and -d-glycero-d-ido-oct-4-ulo-4,8-pyranosonate (5) which were carefully resolved by column chromatography. Compound 4 was transformed into its 2,3-di-O-methyl derivative (6) which was deacetonated to 7 and subsequently degraded to dimethyl 2,3-di-O-methyl-(+)-L-tartrate (8). On the other hand, acetonation of a mixture of 4 and 5 gave the corresponding tri-O-isopropylidene derivatives (9) and (10). Compounds 4 and 5 were reduced with LiAlH₄ to the related 4,5:6,7-di-O-isopropylidene-β-d-glycero-d-galacto- (11) and β-d-glycero-d-ido-oct-4-ulo-4,8-pyranose (12). Treatment of 11 and 12 with acetone/PTSA/CuSO₄ only produced the acetonation at the C-2,3 positions. Finally, compounds 11 and 12 were deacetonated to the corresponding D-glycero-d-galacto- (15) and D-glycero-d-ido-oct.-4-ulose (16).     

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.     

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.     

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.