Synthesis and structural analysis of five novel oligosaccharides prepared by glucosyltransfer from beta-D-glucose 1-phosphate to isokestose and nystose using Thermoanaerobacter brockii kojibiose phosphorylase

Five novel oligosaccharides (tetra-, penta- and hexa-saccharides) were synthesized by glucosyltransfer from beta-D-glucose 1-phosphate to isokestose (O-beta-D-fructofuranosyl-(2-->1)-O-beta-D-fructofuranosyl-(2-->1)-alpha-D-glucopyranoside) or nystose (O-beta-D-fructofuranosyl-(2-->1)-O-beta-D-fructofuranosyl-(2-->1)-O-beta-D-fructofuranosyl-(2-->1)-alpha-D-glucopyranoside) using Thermoanaerobacter brockii kojibiose phosphorylase. The oligosaccharides were identified as 2(2-alpha-D-glucopyranosyl)(m)isokestose; [O-alpha-D-glucopyranosyl-(1-->2)](m)-O-[beta-D-fructofuranosyl-(2-->1)](2)-alpha-D-glucopyranoside: m=1, 2, and 3, and 2(2-alpha-D-glucopyranosyl)(n)nystose; [O-alpha-D-glucopyranosyl-(1-->2)](n)-O-[beta-D-fructofuranosyl-(2-->1)](3)-alpha-D-glucopyranoside: n=1 and 2 using gas liquid chromatography analysis of the methyl derivatives, and MALDI-TOF-MS and NMR measurements of the newly formed oligosaccharides. 1H, 13C NMR signals of each saccharide were assigned using 2D-NMR techniques, including COSY, HSQC, HSQC-TOCSY, HMBC, CH(2)-selected E-HSQC, and CH(2)-selected E-HSQC-TOCSY.     

Synthesis of oligosaccharide derivatives related to those from sanqi, a Chinese herbal medicine from Panax notoginseng

Oligosaccharide derivatives from sanqi, a Chinese herbal medicine derived from Panax notoginseng, methyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, diosgenyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, and methyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranosyl-(1-->4)-beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, were synthesized under standard glycosylation conditions. An unexpected alpha-(1-->4) linkage was formed predominantly in the presence of neighboring participation group during regioselective synthesis of hexasaccharide via 3+3 strategy.     

Glucuronide triterpene saponins from Bersama engleriana

Five 3-O-glucuronide triterpene saponins (1-5) were isolated from the stem bark of Bersama engleriana Gurke along with two known saponins, polyscias saponin C and aralia saponin 15, and one major C-glycoside xanthone, mangiferin. The structures of the saponins were established mainly by means of spectroscopic methods (one- and two-dimensional NMR spectroscopy as well as FAB-, HRESI-mass spectrometry) as 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl]-betulinic acid (1), 3-O-[beta-D-glucopyranosyl-(1-->2)-[beta-D-galactopyranosyl-(1-->3)]-beta-D-glucuronopyranosyl]-oleanolic acid (2), 3-O-[beta-D-glucopyranosyl-(1-->3)-beta-D-glucuronopyranosyl]-28-O-[beta-D-xylopyranosyl-(1-->6)-beta-d-glucopyranosyl]-oleanolic acid (3), 3-O-[beta-D-galactopyranosyl-(1-->3)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl]-oleanolic acid (4), and 3-O-[beta-d-glucopyranosyl-(1-->3)-beta-D-galactopyranosyl-(1-->3)-beta-D-glucuronopyranosyl]-28-O-[beta-d-xylopyranosyl-(1-->6)-beta-D-glucopyranosyl]-oleanolic acid (5).     

Electronic structure calculations as a tool for investigating acyl migrations in ester saponins

The possibility of acyl migrations in ester saponins from Maesa lanceolata was investigated by molecular mechanics and electronic structure calculations carried out on the major constituent maesasaponin IV3 (3beta-O-[[alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-galactopyranosyl-(1-->3)]-[beta-D-galactopyranosyl-(1-->2)]-beta-D-gluco-pyranuronyl]-21beta-angeloyloxy-22alpha-propanoyloxy-13beta,28-oxido-olean-16alpha, 28alpha-diol). It was confirmed that acyl migrations could occur in rings D and E of maesasaponins.     

Haemolytic acylated triterpenoid saponins from Harpullia austro-caledonica

Eight new acylated triterpenoid saponins were isolated from the stem bark of Harpullia austro-caledonica along with the known harpuloside (9). Their structures were established using 1D and 2D NMR and mass spectrometry as 3-O-beta-D-galactopyranosyl-(1-->2)-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylbarringtogenol C (1), 3-O-alpha-L-rhamnopyranosyl-(1-->3)-[beta-D-galactopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloyl barringtogenol C (2), 3-O-alpha-L-arabinofuranosyl-(1-->3)-[beta-D-galactopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylbarringtogenol C (3), 3-O-alpha-L-arabinofuranosyl-(1-->2)-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylprotoaescigenin (4), 3-O-alpha-L-arabinofuranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->2)]-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloyl protoaescigenin (5), 3-O-alpha-L-arabinofuranosyl-(1-->3)-[beta-D-xylopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylprotoaescigenin (6), 3-O-alpha-L-arabinofuranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylprotoaescigenin (7), 3-O-beta-D-xylopyranosyl-(1-->2)-beta-D-glucuronopyranosyl-21 beta, 22 alpha-di-O-angeloylprotoaescigenin (8). The EtOH extract of the stem bark showed in vitro cytotoxic activity against KB cells (90% at 10 microg/ml). At a concentration of 5 microg/ml, the saponin mixture showed haemolytic activity and caused 100% haemolysis of a 10% suspension of sheep erythrocytes.     

A major triterpenoid saponin from Gypsophila oldhamiana

A new saponin, gypoldoside A (1), was isolated from the roots of Gypsophila oldhamiana. On the basis of in-depth NMR-spectroscopic and mass-spectrometric analysis, in combination with chemical evidence, its structure was established as 3-O-{beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta-D-glucuronopyranosyl}quillaic acid 28-[alpha-L-arabinopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl] ester. Compound 1 was found to be highly active against three different human cancer cell lines, with IC50 values in the low micromolar range.     

Triterpenoid saponins from Schefflera arboricola

Nine triterpenoid saponins were isolated from the leaves and stems of Schefflera arboricola. The saponins were characterised, on the basis of chemical and spectral evidence, as 3-O-[alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucuronopyranosyl] oleanolic acid, 3-O-[alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucuronopyranosyl] echinocystic acid, 3-O-[beta-D-apiofuranosyl-(1-->4)-beta-D-glucuronopyranosyl] oleanolic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-ramnopyranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid, 3-O-alpha-L-rhamnopyranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl-(1-->4)-[beta-D-galactopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid, 3-O-alpha-L-rhamnopyranosyl-(1-->4)-[beta-D-galactopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl ester, 3-O-beta-D-apiofuranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid and 3-O-beta-D-apiofuranosyl-(1-->4)-[alpha-L-arabinopyranosyl-(1-->2)-] beta-D-glucuronopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl ester.     

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.     

Preparation of partially benzylated mono-, di-, and trisaccharides by selective cleavage of the beta-fructofuranosidic linkage in fully benzylated sucrose and sucrose-related oligosaccharides under acidic conditions

Several partially benzylated mono-, di-, and trisaccharides having an anomeric hydroxyl group were successfully prepared by selective cleavage of the β-fructofuranosidic linkage in fully benzylated sucrose and sucrose-related oligosaccharides derived from lactosucrose, raffinose, melezitose, stachyose, and nystose under acidic conditions using 1:10 75% aqueous sulfuric acid–dioxane at room temperature for 1 h.     

Synthesis and antitumor activity of icogenin and its analogue

Natural saponin icogenin, namely 25(S)-22-O-methyl-furost-5-en-3beta,26-dio-3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->3)]-beta-D-glucopyranoside, and one of its analogues, 25(S)-22-O-methyl-furost-5-en-3beta,26-dio-3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->3)]-alpha-D-glucopyranoside, were first synthesized via line strategy and convergent approach, respectively. It was observed that icogenin and its analogue show potent antitumor activity in vitro.     

Synthesis of a hexasaccharide that relates to the arabinogalactan epitope.

A hexasaccharide derivative of the arabinogalactan epitope, methyl beta-D-galactopyranosyl-(1-->6)-[alpha-L-arabinofuranosyl-(1-->3)]-beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranosyl-(1-->6)-[alpha-L-arabinofuranosyl-(1-->3)]-alpha-D-galactopyranoside, was synthesized efficiently using a 3+3 strategy. The key step is the preparation of the trisaccharide donor, isopropyl 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->6)-[2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl-(1-->3)]-2,4-di-O-benzoyl-1-thio-beta-D-galactopyranoside, from isopropyl 1-thio-beta-D-galactopyranoside using a one-pot synthesis of a 3,6-differentially protected building block.     

Oligosaccharide polyester and triterpenoid saponins from the roots of Polygala japonica

An oligosaccharide polyester, 1-O-(E)-p-coumaroyl-(3-O-benzoyl)-beta-D-fructofuranosyl-(2-->1)-[6-O-(E)-feruloyl-beta-D-glucopyranosyl-(1-->2)]-[6-O-acetyl-beta-D-glucopyranosyl-(1-->3)-(4-O-acetyl)-beta-D-glucopyranosyl-(1-->3)]-4-O-[4-O-alpha-L-rhamnopyranosyl-(E)-p-coumaroyl]-alpha-D-glucopyranoside (polygalajaponicose I), and four triterpenoid saponins, 3beta, 23, 27-trihydroxy-29-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-olean-12-en-28-oic acid (polygalasaponin XLVII), 3-O-beta-D-glucopyranosyl presenegenin 28-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (polygalasaponin XLVIII), 3-O-beta-D-glucopyranosyl presenegenin 28-O-beta-D-galactopyranosyl-(1-->5)-beta-D-apiofuranosyl-(1-->4)-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranosyl ester (polygalasaponin XLIX) and 2beta, 27-dihydroxy-3-O-beta-D-glucopyranosyl 11-oxo-olean-12-en-23, 28-dioic acid 28-O-beta-D-galactopyranosyl-(1-->5)-beta-D-apiofuranosyl-(1-->4)-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-fucopyranosyl ester (polygalasaponin L), in addition to five known compounds have been isolated from the roots of Polygala japonica.     

Chemo-enzymatic synthesis of a tetra- and octasaccharide fragment of the capsular polysaccharide of Streptococcus pneumoniae type 14

The chemo-enzymatic synthesis is described of tetrasaccharide 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) (1) and octasaccharide beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->6)-[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) (2), representing one and two tetrasaccharide repeating units of Streptococcus pneumoniae serotype 14 capsular polysaccharide. In a chemical approach, the intermediate linear trisaccharide 3 and hexasaccharide 4 were synthesized. Galactose residues were beta-(1-->4)-connected to the internal N-acetyl-beta-D-glucosamine residues by using bovine milk beta-1,4-galactosyltransferase. Both title oligosaccharides will be conjugated to carrier proteins to be tested as potential vaccines in animal models.     

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.     

Glycosylation of dodecyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and dodecyl beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D-glucopyranoside as saccharide primers in cells

Syntheses of oligosaccharides expressed on cells are indispensable for the improvement of the functional analyses of the oligosaccharides and their applications. We are developing saccharide primers for synthesizing oligosaccharides using living cells. In this study, dodecyl 2-acetamido-2-deoxy-beta-D-glucopyranoside (GlcNAc-C12) and dodecyl beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D-glucopyranoside (LacNAc-C12) were examined for their abilities to prime the syntheses of neolacto-series oligosaccharides in HL60 cells. When GlcNAc-C12 was incubated with HL60 cells in serum-free medium for 2 days, 14 kinds of glycosylated products were collected from the culture medium. They were separated by high-performance liquid chromatography. The sequences of the products were determined to be neolacto-series oligosaccharides including Lewis(X), sialyl Lewis(X), polylactosamine, and sialylpolylactosamine by mass spectrometry. GlcNAc-C12 was also glycosylated by B16 cells and gave sialyllactosamine. Furthermore, LacNAc-C12 gave similar glycosylated products to GlcNAc-C12.     

A triterpenoidal saponin and sphingolipids from Pteleopsis hylodendron

From the stem bark of Pteleopsis hylodendron, a triterpenoidal saponin bellericagenin [B 3-O-[beta-D-glucopyranosyl-(1-->2)-alpha-D-glucopyranoside] (1) (Pteleopsoside)] and two sphingolipids, hylodendroside-I (2), and hylodendroside-II (3) were isolated, along with a synthetically known compound, [2alpha, 3beta, 23-triacetoxy-19alpha-hydroxyolean-12-en-28-oic acid (4)]. Other known compounds, friedelin (5), beta-carotene (6), lupeol (7), sitosterol (8), and stigmasterol (9), were also obtained. Their structures were deduced with the help of detailed spectroscopic studies.     

Purification and characterization of stachyose synthase from lentil (Lens culinaris) seeds: galactopinitol and stachyose synthesis.

Stachyose synthase (STS) (EC 2.4.1.67) was purified 313-fold from mature seeds of lentil. The final preparation had a specific activity of 9.09 nkat stachyose formed per milligram of protein. The enzyme was a monomeric protein with a molecular mass of 88.6 kDa (SDS-PAGE) and an isoelectric point of 4.8 (chromatofocusing). Western analysis revealed cross-reactivity of polyclonal antibodies raised against STS from adzuki bean with the lentil enzyme. The purified enzyme catalyzed a range of different galactosyl transfer reactions. In addition to the genuine STS reaction (raffinose + galactinol --> stachyose + myo-inositol), the enzyme catalyzed the reversible galactosyl transfer from galactinol to d-pinitol (1d-3-O-methyl-chiro-inositol), yielding galactopinitol A (O-alpha-d-galactopyranosyl-(1 --> 2)-4-O-methyl-d-chiro-inositol) and myo-inositol. Galactopinitol A could be further galactosylated by STS to give ciceritol (O-alpha-d-galactopyranosyl-(1 --> 6)-O-alpha-d-galactopyranosyl-(1 --> 2)-4-O-methyl-d-chiro-inositol). Enzymatic synthesis of galactopinitol A and ciceritol is a new observation. However, STS was not only able to utilize galactopinitol A as galactosyl acceptor, but also as galactosyl donor to form stachyose from raffinose. The role of STS in the metabolism of galactosyl cyclitols and oligosaccharides in plant seeds is discussed.     

Action of Arthrobacter ureafaciens inulinase II on several oligofructans and bacterial levans.

1. Arthrobacter ureafaciens inulinase II which converts inulin to di-D-fructofuranose 1,2' : 2,3' dianhydride (difructose anhydride III) leaving a small amount of oligosaccharides, was investigated in order to characterize its mode of action. 2. After the enzymatic reaction on the glucose-terminated inulin molecules had been completed, the oligosaccharides left in the enzyme digest were isolated, and identified to be the fructose-glucose oligosaccharides; O-beta-D-fructofuranosyl-(2 leads to 1)-O-beta-D-fructofuranosyl alpha-D-glucopyranoside (1-kestose), O-beta-D-fructofuranosyl-[(2 leads to 1)-O-beta-D-fructofuranosyl]2 alpha-D-glucopyranoside and O-beta-D-fructofuranosyl-[(2 leads to 1)-O-beta-D-fructofuranosyl]3 alpha-D-glucopyranoside. The difructose anhydride formation from the three fructose-glucose oligosaccharides in the separate reaction system with an increased substrate concentration was observed only with the latter two substrates, but not with the first one. 3. The difructose anhydride formation with several (2 leads to 1)-beta-linked fructose oligosaccharides and bacterial (2 leads to 6)-beta-fructans was examined. The (2 leads to 1)-beta-linked fructose oligosaccharides were effective as substrates for the enzyme with the exception of inulobiose, but the (2 leads to 6)-beta-fructans remained unaffected. 4. It was concluded that the enzyme attacks (2 leads to 1)-beta-linked fructan molecules from the nonreducing fructose ends and requires the presence of at least two adjacent (2 leads to 1)-beta-fructofuranosyl linkages.     

Purification and characterisation of a galactoglucomannan from kiwifruit (Actinidia deliciosa)

A galactoglucomannan (GGM) has been purified from the primary cell walls of ripe kiwifruit. A combination of barium hydroxide precipitation, anion exchange- and gel-permeation chromatography gave a chemically homogeneous polymer with a 1:2:2 galactose-glucose-mannose ratio and a molecular weight range of 16-42 kDa. Complete hydrolysis of the polymer with endo-1,4-beta-mannanase (EC 3.2.1.78) from Aspergillus niger gave a mixture of oligosaccharides, three of which (II, III, IV) accounted for more than 80% of the GGM. Structural characterisation of these oligosaccharides and the original polysaccharide was achieved by linkage analysis, 1D and 2D NMR spectrometry and enzymatic hydrolysis. Oligosaccharide II beta-D-Glcp-(1-->4)-beta-D-Manp-(1-->, III beta-D-Glcp-(1-->4)-[alpha-D-Galp-(1-->6)]-beta-D-Manp-(1-->, and IV beta-D-Glcp-(1-->4)-[beta-D-Galp-(1-->2)-alpha-D-Galp-(1-->6)]-beta-D-Manp-(1-->4)-beta-D-Glcp-(1-->4)-beta-D-Manp-(1-->, appeared in the molar ratio of 2:1:1. A trace amount of mannobiose (I) was detected, indicating that some of the mannosyl residues were contiguous. It is concluded that the predominant structural feature of kiwifruit GGM is a backbone of alternating beta-(1-->4)-linked D-glucopyranosyl and D-mannopyranosyl residues, with approximately one third of the latter carrying side-chains at 0-6 of single alpha-D-Galp-(1--> residues (50% of the branches) or the disaccharide beta-D-Galp-(1-->2)-alpha-D-Galp-(1--> (50% of the branches), the substituted residues being separated by three or five unsubstituted monosaccharide units.     

Synthesis of a tetrasaccharide representing a minimal epitope of an arabinogalactan

The hydrophobic alkyl chain-containing tetrasaccharide, dodecyl beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranosyl-(1-->6)-[alpha-L - arabinofuranosyl-(1-->2)]-beta-D-galactopyranoside, was synthesized efficiently using a convergent strategy. In coupling reactions, protected trichloroacetimidates proved to be better donors than their corresponding bromides in the preparation of the dodecyl disaccharide and trisaccharide. Zemplén deacylation provided the target tetramer in good overall yield.