Linear Synthesis of The Methyl Glycosides of Tri-, Tetra-, and Pentasaccharide Fragments of The Shigella Flexneri Serotype 5A O-Antigen

ABSTRACT

The stepwise synthesis of methyl α-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (EBC-OMe, 1), methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (A(E)BC-OMe, 2), and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (DA(E)BC-OMe, 3) is described. Compounds 1, 2 and 3 constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Methyl 2,4-di-O-benzoyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside was an appropriate BC precursor for the synthesis of 1. For the synthesis of the branched targets 2 and 3, a benzyl group was best suited at position 2 of rhamnose C. Thus, methyl 4-O-benzyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside was the key intermediate to the BC portion. In all cases, 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride was a convenient E precursor, when used in combination with titanium tetrafluoride. All along, attention was paid to steric hindrance as a factor of major impact on the condensation steps outcome. Therefore, based on previous experience, 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate and 3,4,6-tri-O-acetyl-2-deoxy-2-trichloroacetamido-α-D-glucopyranosyl trichloroacetimidate were used as donors. Both suited all requirements when used as key precursors for residues A and D in the synthesis of 3, respectively.     

Linear Synthesis of the Methyl Glycosides of Tetra- and Pentasaccharide Fragments Specific for the Shigella flexneri Serotype 2a O-Antigen

ABSTRACT

Starting from the known methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2-O-benzoyl-α-L-rhamnopyranoside, the stepwise linear syntheses of methyl α-L-rhamnopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→ 3)-[α-D-glucopyranosyl-(1→ 4)]-α-L-rhamnopyranoside (AB(E)C, 4), and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→ 2)-α-L-rhamnopyranosyl-(1→ 3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (DAB(E)C, 5) are described; these constitute the methyl glycosides of a branched tetra- and pentasaccharide fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a, respectively. The chemoselective O-deacetylation at position 2_B and/or 2_A of key tri- and tetrasaccharide intermediates bearing a protecting group at position 2_C was a limiting factor. As such a step occurred once in the synthesis of 4 and twice in the synthesis of 5, the regioselective introduction of residue A on a B(E)C diol precursor (12) and that of residue D on an AB(E)C diol precursor (19) was also attempted. In all cases, a trichloroacetimidate donor was involved. The latter pathway was found satisfactory for the construction of the target 4 using the appropriate tri-O-benzoyl rhamnosyl donor. However, attempted chain elongation of 12 using 2-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranosyl trichloroacetimidate (8) resulted in an inseparable mixture which needed to be benzoylated to allow the isolation of the target tetrasaccharide. Besides, condensation of the corresponding tetrasaccharide acceptor and the N-acetylglucosaminyl donor was sluggish. As the target pentasaccharide was isolated in a poor yield, this route was abandoned.     

Synthesis of a Tri- and Tetrasaccharide Fragment Specific for the Shigella flexneri Serotype 5a O-Antigen. A Reinvestigation

ABSTRACT

Stereocontrolled, stepwise synthesis of methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (A(E)B, 1) and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (DA(E)B, 2) is described; these constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Two routes to trisaccharide 1 were considered. Route 1 involved the coupling of a precursor to residue A and a disaccharide EB, whereas route 2 was based on the condensation of a precursor to residue E and a disaccharide AB. Rather surprisingly, the latter afforded the β-anomer of 1, namely methyl α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside as the major product. Route 1 was preferred. Overall, several observations made during this study suggested that, for the construction of higher fragments, a suitable precursor to rhamnose A would require protecting groups of low bulkiness at position 3 and 4. Therefore, the 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate (35) was the precursor of choice to residue A in the synthesis of the tetrasaccharide 2. The condensation product of 35 and methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-4-O-benzyl-α-L-rhamnopyranoside was selectively deacylated and condensed to 2-trichloroacetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl trichloroacetimidate to afford the corresponding fully protected tetrasaccharide 45. Controlled stepwise deprotection of the latter proceeded smoothly to afford the target 2. It should be emphasised that the preparation of 45 was not straightforward, several donors and coupling conditions that were tested resulted only in the complete recovery of the acceptor. Distortion of several signals in the ¹³C NMR spectra of the fully or partially protected tetrasaccharide intermediates suggested that steric hindrance, added to the known low reactivity of HO-2 of rhamnosyl acceptors, probably played a major role in the outcome of the glycosidation attempts.     

Synthesis of the Methyl Glycosides of a Di- and Two Trisaccharide Fragments Specific for the Shigella flexneri Serotype 2a O-Antigen

ABSTRACT

The stereocontrolled synthesis of methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (EC, 1), methyl α-L-rhamnopyranosyl-(1→3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (B(E)C, 3) and methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside (ECD, 4) is described; these constitute the methyl glycosides of branched and linear fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a. Emphasis was put on the construction of the 1,2-cis EC glycosidic linkage resulting in the selection of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (8) as the donor. Condensation of methyl 2,3-O-isopropylidene-4-O-trimethylsilyl-α-L-rhamnopyranoside (11) and 8 afforded the fully protected αE-disaccharide 20, as a common intermediate in the synthesis of 1 and 3, together with the corresponding βE-anomer 21. Deacetalation and regioselective benzoylation of 20, followed by glycosylation with 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (15) afforded the branched trisaccharide 25. Full deprotection of 20 and 25 afforded the targets 1 and 3, respectively. The corresponding βE-disaccharide, namely, methyl β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (βEC, 2) was prepared analogously from 21. Two routes to trisaccharide 4 were considered. Route 1 involved the coupling of a precursor to residue E and a disaccharide CD. Route 2 was based on the condensation of an appropriate EC donor and a precursor to residue D. The former route afforded a 1:2 mixture of the αE and βE condensation products which could not be separated, neither at this stage, nor after deacetalation. In route 2, the required αE-anomer was isolated at the disaccharide stage and transformed into 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2,3-di-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (48) as the EC donor. Methyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-β-D-glucopyran-oside (19) was preferred to its benzylidene analogue as the precursor to residue D. Condensation of 19 and 48 and stepwise deprotection of the glycosylation product afforded the target 4.     

Preparation of trans Diequatorial 2,3-Pyruvate Acetals in a Di- and a Trisaccharide Related to the K-Antigen from E. Coli 0101:K103:H−

Abstract

Using methyl 2,2-bis(ethylthio)propionate as acetalating agent and triflic acid-sulfuryl chloride as catalyst, synthesis of 2,3-trans diequatorial pyruvate ketal was achieved. Starting from D-galactose and L-rhamnose derivatives, methyl 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl-(1→4)-6-O-benzyl-2,3-O-(1-methoxycarbonyl)ethylidene- α-D-galactopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside and methyl 4,6-di-O-benzyl-2,3-O-(1-methoxy-carbonyl)ethylidene-α-D-galactopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside were synthesized. Removal of the protecting groups from the former, afforded the trisaccharide repeating unit of the K-antigen from E.coli O101:K103:H^? in the form of its methyl glycoside methyl ester.     

Synthesis of Rhamnogalacturonan I Fragments

ABSTRACT

The partially deprotected trisaccharide 17 has been synthesized as an analogue of the repeating unit of the backbone of rhamnogalacturonan I. The trisaccharide 17 was obtained after prior selective derivatization of HO-3 and HO-4 of a rhamnopyranose cyanoethylidene glycosyl donor, followed by coupling with a tritylated galactopyranosyluronic acceptor (11), selective removal of the acetyl group at the O-2' position of the formed disaccharide 12, and glycosylation of the HO-2' position with methyl (ethyl 2,3-di-O-benzyl-4-O-p-methoxybenzyl-1-thio-β-D-galactopyranosid)uronate (14) providing methyl (methyl 2,3-di-O-benzyl-4-O-p-methoxybenzyl-α-D-galactopyranosyluronate)-(1→2)-(4-O-benzoyl-3-O-benzyl-α-L-rhamnopyranosyl)-(1→4)-(allyl 2,3-di-O-benzyl-β-D-galactopyranosid)uronate (15). Finally, palladium chloride catalyzed deallylation (16) and hydrogenolysis over Pd-C resulted in methyl (methyl α-D-galactopyranosyluronate)-(1→2)-(4-O-benzoyl-α-L-rhamnopyranosyl)-(1→4)-α/β D-galactopyranuronate (17).     

Triterpenoid saponins from the buds of Lonicera similis

Four new lupane triterpenoid saponins, along with one known lupane and eight hederagenin saponins, were isolated from the EtOH extract of the buds of Lonicera similis Hemsl. The structures of the new compounds were established as 3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl 23-hydroxybetulinic acid 28-O-β-D-glucopyranosyl ester (lonisimilioside A, 1), 3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl 23-hydroxybetulinic acid 28-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl ester (lonisimilioside B, 2), 3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl betulinic acid 28-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl ester (lonisimilioside C, 3) and 3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl betulinic acid 28-O-β-D-glucopyranosyl ester (lonisimilioside D, 4), respectively. The cytotoxic activities of the isolates against human cancer cell lines HepG2, MCF-7 and A-549 were evaluated. Only the monodesmosidic saponin with a free carboxyl group at C-28 (12) exhibited significant cytotoxicities against HepG2, MCF-7 and A-549 cell lines with the IC₅₀ values of 8.98 ± 0.19, 12.48 ± 0.45 and 11.62 ± 0.54 μM, respectively. Furthermore, Hoechst fluorescence 33342 staining was used to demonstrate that 12 could induce HepG2 and A-549 cells apoptosis significantly.     

Antibacterial activity of a triterpenoid saponin from the stems of Caesalpinia pulcherrima Linn.

A new compound 1 was isolated from the methanolic extract of the stems of the Caesalpinia pulcherrima Linn. along with a reported compound (2) 3-O-β-D-glucopyranosyl-(1→4)-β-D-xylopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl hederagenin 28-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl ester. The new compound 1 has m.p. 272–274°C, m.f. C₄₆H₇₄O₁₇, [M]⁺ m/z 898. It was characterised as 3-O-β-D-glucopyranosyl-(1→4)-α-L-arabinopyranosyl hederagenin 28-O-β-D- xylopyranosyl ester by various colour reactions, chemical degradations and spectral analyses. Antibacterial activity of compound 1 was screened against various Gram-positive and Gram-negative bacteria and showed significant results.     

A novel dimeric flavonol glycoside from Cynanchum acutum subsp. sibiricum

A novel dimeric flavonol glycoside, Cynanflavoside A (1), together with six analogues, kaempferol-3-O-α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranoside (2), quercetin-3-O-α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranoside (3), kaempferol-3-O-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranoside (4), quercetin-3-O-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranoside (5), kaempferol-3-O-β-D-glucopyranosyl-7-O-α-L-rhamnopyranoside (6), and quercetin-3-O-galactoside (7) were isolated from the n-butyl alcohol extract of Cynanchum acutum subsp. sibiricum. Their structures were determined spectroscopically and compared with previously reported spectral data. All compounds were evaluated for their anti-complementary activity in vitro, and only compound 5 exhibited anti-complement effects with CH₅₀ value of 0.33 mM.     

Synthesis of glycosaminoglycans via enzymatic polymerization

Hyaluronic acid and chondroitin were successfully synthesized as representative molecules of glucosaminoglycans and galactosaminoglycans found in a glycosaminoglycan family via enzymatic polymerization catalyzed by testicular hyaluronidases. A newly designed N-acetylhyalobiuronate oxazoline derivative with a β-D -glucuronyl-(1→3)-N-acetyl-D -glucosamine disaccharide structure served as a transition-state analogue substrate monomer for the enzyme, giving rise to artificial hyaluronic acid in 52% yields with a number-average molecular weight of 1.35 × 10⁴ through ring-opening polyaddition in a perfect regioselective and stereoselective manner. A novel N-acetylchondrosine oxazoline derivative with a β-D -glucuronyl-(1→3)-N-acetyl-D -galactosamine disaccharide structure also acted as a transition-state analogue substrate monomer for the enzyme, yielding artificial chondroitin in 35% yields with a number-average molecular weight of 2.5 × 10³. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3541–3548, 2003     

Chemical structure and biological activity of steroidal saponins from Furcraea gigantea

A new bisdesmosidic furostanol saponin, along with a known spirostanol saponin, furcreastatin, were isolated from Furcraea gigantea Vent. (Agavaceae). The structure of the new saponin was elucidated as 3-[(O-6-deoxy-α-L-mannopyranosyl-(1→4)-O-β-D-glucopyranosyl-(1å 3)-O-[O-β-D-glucopyranosyl-(1→3)-β-D-glucopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→4)-β-D-galactopyranosyl)oxy]-(3β, 5α, 25R)-26-(β-D-glucopyranosyloxy)-22-hydroxyfurost-12-one. The structural identification was performed using a combination of spectroscopic techniques and chemical conversions. Furcreastatin showed a powerful haemolytic effect in the in vitro assay, but the new bisdesmosidic furostanol saponin demonstrated only a significant inhibition of the capillary permeability activity.     

Isolation,structural determination and cytotoxic activity of two new ceramides from the root of <Emphasis Type="Italic">Isatis indigotica</Emphasis>

Two new ceramides were isolated from the 95% EtOH extract of traditional Chinese medicinal plant Isatis indigotica. Their structures were elucidated as 1-O-β-D-glucopyranosyl-(2S, 3R)-N-(2′-hydroxype-ntacosanoyl)-octadeca-11E-sphingenine (1) and 1-O-β-D-glucopyranosyl-(2S,3R)-N-(2′-hydroxyhe xacosanoyl)-octadeca-11E-sphingenine (2) on the basis of spectroscopic data. Their cytotoxic effects were evaluated by using MTT method.     

Synthetic Studies on Sialoglycoconjugates 104: Synthesis of Kdn-Lewis X Ganglioside Analogs Containing Modified Reducing Terminal and L-Rhamnose in Place of L-Fucose 1 2

Abstract

KDN-Le^x ganglioside analogs (10, 13, 16 and 19) containing the modified reducing terminal and L-rhamnose in place of L-fucose have been synthesized. Glycosidation of methyl 2,3,4-tri-O-benzyl-1-thio-α-L-rhamnopyranoside (1) with 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-α-D-galacopyranoside (2), followed by reductive ring opening of the benzylidene acetal, gave 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-α-L-rhamnopyranosyl)-(1→3)-O-(2-acet-amido-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 (4). The tetrasaccharide 4 was coupled with methyl O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-galactopyranoside(5), using dimethyl(methylthio)sulfonium triflate (DMTST), to give the hexasaccharide 6, which was converted into compound 11 in the usual manner. Compounds 8 and 11 were transformed, via bromination of the reducing terminal, radical reduction, O-deacylation and saponification of the methyl ester, into the desired KDN-Le^x hexasaccharides (10, 13). On the other hand, glycosylation of 2-(tetradecyl)hexadecanol with α-trichloroacetimidates 14 and 17, afforded the target ganglioside analogs 16 and 19.

     

Novel dammarane-type saponins from Gynostemma pentaphyllum and their neuroprotective effect

Abstract

Three novel dammarane-type saponins, 2α,3β,12β,20(S),24(S)-pentahydroxydammar-25-ene-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-glucopyranoside (1, namely gypenoside J1), 2α,3β,12β,20(S),25-pentahydroxydammar-23-ene-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-glucopyranoside (2, namely gypenoside J2) and 2α,3β,12β,20(S)-tetrahydroxydammar-25-en-24-one-3-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-20-O-β-D-xylopyranosyl-(1→6)-β-D-glucopyranoside (3, namely gypenoside J3) along with one known gypenoside (gypenoside LVII) were isolated from the aerial parts of G. pentaphyllum using various chromatographic methods. Their structures were elucidated on the basis of IR, 1D- (¹H and ¹³C), 2D-NMR spectroscopy (HSQC, HMBC and COSY), and mass spectrometry (ESI-MS/MS). Their activity was tested using CCK-8 assay. These four compounds showed little anti-cancer activity with IC₅₀ values more than 100?μM against four types of human cancer lines. The effects of them against H₂O₂-induced oxidative stress in human neuroblastoma SH-SY5Y cells were evaluated and they all showed potential neuroprotective effects with 3.64–18.16% higher cell viability than the H₂O₂-induced model group.     

Haplosinine — A new furanoquinoline glycoalkaloid from Haplophyllum perforatum

The new glycoalkaloid haplosinine has been isolated from the epigeal part ofHaplophyllum perforatum (M. B.) Kar. et Kir., and its structure has been established on the basis of chemical transformations and a comparative analysis of its¹³C NMR spectra with those of known compounds as haplopine 7-O-[O-β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranoside].     

Glucuronidase-assisted Transglycosylation for the Synthesis of Highly Functional Disaccharides: β-D-Glucuronyl 6-O-Sulfo-β-D-Gluco- and -β-D-Galactopyranosides

The substrate specificity of snail (Helix pomatia and Helix aspersa), limpet (Patella vulgata), and bovine glucuronidases was examined by using p-nitrophenyl glucuronide (GlcA-O-pNP) and p-nitrophenyl 6-O-sulfo-β-D-glycopyranosides as the glycosyl donor and acceptors, respectively. When the donor was treated with these enzymes in the absence of the acceptors, β (1 → 3) glucuronyl disaccharides were obtained as the major products together with β (1 → 2) isomers as the result of an enzymatic “self-transglycosylation” reaction. When p-nitrophenyl 6-O-sulfo-β-D-glucopyranosides (6-O-sulfo-Glc-O-pNP and 6-O-sulfo-Glc-S-pNP) were applied as acceptor substrates, every glucuronidase transferred the GlcA residue to either the O-3 or O-2 position in 6-O-sulfo-Glc to yield a mixture of GlcAβ (1 → 3)- and GlcAβ (1 → 2)-linked disaccharides in a ratio of 12:1 ～ 1:1. On the other hand, when p-nitrophenyl 6-O-sulfo-β-D-galactopyranosides (6-O-sulfo-Gal-O-pNP and 6-O-sulfo-Gal-S-pNP) were applied, limpet and bovine glucuronidases gave a GlcAβ (1 → 3)-linked disaccharide regioselectively, while the snail enzymes showed no reactivity.     

Isolation and Structural Study on Carbohydrates from Cynanchum otophyllum and Cynanchum paniculatum

Three new carbohydrates were isolated from the acidic hydrolysis part of the ethyl acetate extract of Cynanchum otophyllum Schneid (Asclepiadaceae) and one new carbohydrate from the ethyl acetate extract of Cynanchum paniculatum Kitagawa. Their structures were determined as methyl 2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranosyl-(1 → 4)-2,6-deoxy-3-O-methyl-β-D-arabino-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranoside (1), ethyl 2,6-dideoxy-3-O-methyl-β-D-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-l-lyxo-hexopyranoside (2), met hyl 2,6-dideoxy-3-O-methyl-α-l-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-β-D-lyxo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranoside (3), and 2,6-dideoxy-3-O-methyl-β-D-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-d-arabino-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α -d-arabino-hexopyranose (4), respectively, by spectral methods.     

Synthesis of Sialyl Lewis X Ganglioside Analogs Containing A Variable Length Spacer Between the Sugar and Lipophilic Moieties 1

Abstract

Five sialyl Lew is X ganglioside analogs containing 4-(2-tetradecylhexadecanoylamino)benzyl group in place of ceramide and a variety of lengths of ethylene glycol chains as the spacer, have been synthesized. Glycosidation of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-glacto-2-nonulopyranosylonate)-(2→3)-O-(4-O-acetyl-2,6-di-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-acetylα-L-fucopyranosyl)-(1→3)]-2,4-di-O-benzoyl-α-D-glucopyranosyl trichloroacetimidate (13) with oligo ethyleneglycol monobenzyl ether derivatives 9, 10, 11 and 12, prepared from the corresponding oligo ethyleneglycols by 4-nitrobenzylation, reduction and N-acylation with 2-tetradecylhexadecanoic acid, using boron trifluoride etherate gave the corresponding glycolipid derivatives 14, 15, 16 and 17. A similar glycosidation of 13 with 4-nitrobenzyl alcohol gave the 4-nitrobenzyl glycoside 18, which was converted via reduction of nitro group and N-acylation into the corresponding glycolipid derivative 19. Compounds 14-17 and 19 were transformed into the title compounds by O-deacylation and hydrolysis of methyl ester group in good yields.

     

A new ceramide from the root of <Emphasis Type="Italic">Isatis Indigotica</Emphasis> and its cytotoxic activity

In addition to two ceramides 1-O-β-D-glucopyranosyl-(2S,3R)-N-(2'-hydroxyhexadecanoyl)-octadeca-4E,8Esphingenine (2) and (2S,3S,4R)-N-(2'-hydroxytetracosanoyl)-octadecasphingenine (3), which separated for the first time, a new ceramide 1-O-β-D-glucopyranosyl-(2S,3R)-N-(2'-hydroxyhexacosanoyl)octadecasphingenine (1) was isolated from the traditional Chinese medicinal herb Isatis indigotica. Their cytotoxic effects were evaluated by the MTT method.     

Synthesis of Tetrasaccharide Repeating Unit of the K-Antigen from Klebsiella Type-16

Abstract

Starting from L-fucose, D-glucose and lactose, methyl O-[2,3-di-O-benzoyl-4, 6-O-(4-methoxybenzylidene)-β-D-glucopyranosyl]-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside and methyl O-(2,3,4,6-tetra-O-benzyl-β-D-galactopyranosyl)-(1→4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1→4)-O-(methyl 2,3-di-O-benzoyl-β-D-glucopyranosyluronate)-(1→4)-2,3-di-O-benzoyl-α-L-fucopyranoside were synthesized. Removal of protecting groups gave the tetrasaccharide repeating unit of the antigen from Klebsiella type-16 in the form of its methyl ester methyl glycoside.