Synthesis of a tetrasaccharide donor corresponding to the O-specific polysaccharide of Shigella dysenteriae type 1

O-(2,4-Di-O-chloroacetyl-α-l-rhamnopyranosyl)-(1 → 2)-O-(3,4,6-tri-O-benzoyl-α-d-galactopyranosyl)-(1 → 3)-O-(2-acetamido-4,6-di-O-acetyl-2-deoxy-α-d-glycopyranosyl)-(1 → 3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (1) was synthesized in a stepwise manner, using the following monosaccharide units: 2-(trimethylsilyl)ethyl 2,4-di-O-benzoyl-α-l-rhamnopyranoside, 2-azido-4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-β-d-glycopyranosyl chloride, methyl 3,4,6-tri-O-benzoyl-2-O-(4-methoxybenzyl)-1-thio-β-d-galactopyranoside, and 2,4-di-O-benzoyl-3-O-chloroacetyl-α-l-rhamnopyranosyl chloride. Compound 1 corresponds to a complete tetrasaccharide repeating unit of the O-specific polysaccharide of the lipopolysaccharide of Shigella dysenteriae type 1.     

Synthesis of two purple-membrane glycolipids and the glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol

The two purple-membrane glycolipids O-β-d-glucopyranosyl- and O-β-d-galactopyranosyl-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2, 3-di-O-phytanyl-sn-glycerol were prepared by coupling O-(2,3,4-tri-O-acetyl-α-d-mannopyranosyl)-(1→2)-O-(3,4,6-tri-O-acetyl-α-d-glucopyranosyl)-(1→1)-2, 3-di-O-phytanyl-sn-glycerol (9) with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide, respectively, followed by deacetylation. The glycolipid sulfate O-(β-d-glucopyranosyl 3-sulfate)-(1→6)-O-α-d-mannopyranosyl-(1→2)-O-α-d-glucopyranosyl-(1→1)-2,3-di-O-phytanyl-sn-glycerol was prepared by coupling of 9 with 2,4,6-tri-O-acetyl-3-O-trichloroethyloxycarbonyl-α-d-glucopyranosyl bromide in the presence of Hg(CN)₂/HgBr₂ followed by selective removal of the 3?-trichloroethyloxycarbonyl group, sulfation of HO-3?, and deacetylation. The suitably protected key-intermediate 9 could be prepared by two distinct approaches.     

Synthesis of 3- and 2′-fucosyl-lactose and 3,2′-difucosyl-lactose from partially benzylated lactose derivatives

O-β-d-Galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose has been synthesised by reaction of benzyl 2,6-di-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-β-d-galactopyranosyl)-β-d-glucopyranoside with 2,3,4-tri-O-benzyl-α-l-fucopyranosyl bromide in the presence of mercuric bromide, followed by hydrogenolysis. Benzylation of benzyl 3′,4′-O-isopropylidene-β-lactoside, via tributylstannylation, in the presence of tetrabutylammonium bromide or N-methylimidazole, gave benzyl 2,6-di-O-benzyl-4-O-(6-O-benzyl-3,4-O-isopropylidene-β-d-galactopyranosyl)-β-d-glucopyranoside (6). α-Fucosylation of 6 in the presence of tetraethylammonium bromide provided either benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyransoyl)-β-d- galactopyranosyl]-β-d-glucopyranoside (13, 73%) or a mixture of 13 (42%) and benzyl 2,6-di-O-benzyl-4-O-[6-O-benzyl-3,4,-O-isopropylidene-2-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d- galactopyranosyl-3-O-(2,3,4-tri-O-benzyl-α-l-fucopyranosyl)-β-d-glucopyranoside (16, 34%). α-Fucosylation of 13 in the presence of mercuric bromide and 2,6-di-tert-butyl-4-methylpyridine gave 16 (73%). Hydrogenolysis and acid hydrolysis of 13 and 16 afforded O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-d-glucose and O-α-l-fucopyranosyl-(1→2)-O-β-d-galactopyranosyl-(1→4)-O-[α-l-fucopyranosyl-(1→3)]-d-glucose, respectively.     

G.L.C.-M.S. of partially methylated and acetylated derivatives of 3-deoxyoctitols

Partially methylated and acetylated 3-deoxyoctitols were prepared from derivatives of 3-deoxy-d-manno-2-octulosonic acid (KDO), and identified as the d-glycero-d-talo and d-glycero-d-galacto isomers by g.l.c.-m.s. Mono- and oligosaccharide derivatives of KDO were subjected in sequence to methylation, carboxyl-reduction, hydrolysis, carbonyl-reduction, and acetylation to yield 1,2,6-tri-O-acetyl-3-deoxyoctitol derivatives. Carboxyl-reduction and then methylation gave the series of 2,6-di-O-acetyl derivatives. Oligosaccharides with KDO at the reducing end, e.g., β-d-ribofuranosyl-(1→7)-KDO, α-l-glycero-d-manno-heptopyranosyl-(1→5)-KDO, and α-KDOp-(2→4)-KDO, yielded, after carbonyl-reduction, methylation, carboxyl-reduction, hydrolysis, and acetylation, the 1,7-, 1,5-, and 1,4-di-O-acetyl derivatives, whereas remethylation after carboxyl-reduction gave the 7-, 5-, and 4-O-acetyl derivatives of 3-deoxyoctitol. General rules for the fragmentation of 3-deoxyoctitols during e.i.-m.s. were established.     

Sequential synthesis and 13C-N.m.r. spectra of methyl β-glycosides of (1→4)-β-d-xylo-oligosaccharides

The reaction of 2,3-di-O-acetyl-4-O-benzyl-α,β-d-xylopyranosyl bromide (2) with methyl 2,3-di-O-acetyl-β-d-xylopyranoside gave methyl O-(2,3-di-O-acetyl-4-O-benzyl-β-d-xylopyranosyl)-(1→4)-2,3-di-O-acetyl-β-d-xylopyranoside (22). Catalytic hydrogenolysis of 22 exposed HO-4′ which was then condensed with 2. This sequence of reactions was repeated three more times to afford, after complete removal of protecting groups, a homologous series of methyl β-glycosides of (1→4)-β-d-xylo-oligosaccharides. ¹³C-N.m.r. spectra of the synthetic methyl β-glycosides (di- to hexa-saccharide) are presented together with data for six other, variously substituted, homologous series of (1→4)-d-xylo-oligosaccharides.     

Unusual properties of glycuronans [poly(glycosyluronic) compounds]

2-Methyl-[3,6-di-O-acetyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-glucopyrano]-[2,1-d]-2-oxazoline (4) was prepared from 2-acetamido-3,6-di-O-acetyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d- glucopyranosyl chloride. Condensation of 3,4:5,6-di-O-isopropylidene-d-mannose dimethyl acetal with 4 in the presence of a catalytic amount of p-toluenesulfonic acid afforded O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-(1 → 4)-O-(2-acetamido-3,6-di-O-acetyl-2-deoxy-β-d-glucopyranosyl)-(1 → 2)-3,4:5,6-di-O-isopropylidene-d-mannose dimethyl acetal (6) in 8.6% yield. Catalytic deacetylation of 6 with sodium methoxide, followed by hydrolysis with dilute sulfuric acid, gave O-β-d-galactopyranosyl-(1 → 4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1 → 2)-d-mannose (7). The inhibitory activities of 7 and related sugars against the hemagglutinating activities of various lectins were assayed, and 7 was found to be a good inhibitor against Phaseolus vulgaris hemagglutinin.     

The synthesis and properties of benzylated oxazolines derived from 2-acetamido-2-deoxy-D-glucose

2-Methyl-(2-acetamido-3,4,6-tri-O-benzyl-1,2-dideoxy-α-D-glucopyrano)-[2,1-d]-2-oxazoline,2-methyl-(2-acetamido-6-O-acetyl-3,4-di-O-benzyl-1,2-dideoxy-α-D-glucopyrano)-[2,1-d]-2-oxazoline,and 2-methyl-(2-acetamido-4-O-acetyl-3,6-di-O-benzyl-1,2-dideoxy-α-D-glucopyrano)-[2,1-d]-2-oxazoline were synthesized from the allyl 2-acetamido-3,4,6-tri-O-benzyl-2-deoxy-D-glucopyranosides, and from the 3,4-di-O-benzyl or 3,6-di-O-benzyl analogs, respectively, both the α and β anomer being used in each case. The preparation of allyl 2-acetamido-3,4,6-tri-O-benzyl- and 3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside is also described. Treatment of the tri-O-benzyl oxazoline with dibenzyl phosphate gave a pentabenzylglycosyl phosphate, from which all the benzyl groups were removed by catalytic hydrogenation, giving 2-acetamido-2-deoxy-α-D-glucopyranosyl phosphate. The corresponding β anomer was not detectable. Treatment of the 3,4-, or 3,6-, di-O-benzyl oxazoline with allyl 2-acetamido-3,4-di-O-benzyl-α-D-glucopyranoside readily gave disaccharide products from which the protecting groups were removed, to give the (1→6)-linked isomer of di-N-acetylchitobiose. Under both acidic and basic conditions, this isomer was less stable than the (1→4)-linked compound.Attempts to employ the 3,6-di-O-benzyl oxazoline for the formation of (1→4)-linked disaccharides, by treatment with either anomer of allyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-D-glucopyranoside, were not very successful, presumably owing to hindrance by the bulky benzyl groups.     

Entwicklung eines syntheseblocks der 3-O-β-d-galactopyranosyl-d-galactopyranose

In the presence of trimethylsilyl triflate, 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose reacted with benzyl 4-O-acetyl-2,6-di-O-benzyl-β-d-galactopyranoside to give benzyl 2,6-di-O-benzyl-3-O-β-d-galactopyranosyl-β-d-galactopyranoside further converted into the synthetic block 1,2,4,6-tetra-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d-galactopyranose. This, in the presence of a Lewis acid catalyst and with the corresponding glycosyl acceptors, gave 8-methoxycarbonyloctyl 3-O-β-d-galactopyranosyl-β-d-galactopyranoside and 8-methoxycarbonyloctyl O-β-d-galactopyranosyl-(1→3)-O-β-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-α-d-galactopyranoside.     

18-Norspirostanol derivatives from Trillium tschonoskii

Three 18-norspironstanol oligoglycosides partly acylated in their sugar moieties were isolated from the underground parts of Trillium tschonoskii. Their structures were characterized, as 1-O-[2″,3″,4″-tri-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin-24-O-acetate, 1-O-[2″,3″,4″-tri-O-acetyl-α-l-rhamno-pyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin and 1-O-[2″,4″-di-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl]-epitrillenogenin-24-O-acetate.     

A pregnane ester glycoside from Periploca calophylla

A new pregnane ester genin, plocigenin, and a new pregnane ester diglycoside, plocin, have been isolated from the dried twigs of Periploca calophylla. The chemical and spectroscopic properties are consistent with the structures 12,20-di-O-benzoyl drevogenin-D and 12,20-di-O-benzoyl drevogenin-D-3-O-β-D-oleandropyranosyl (1 → 4)-O-β-oleandropyranoside, respectively.     

Two pregnane ester glycosides from Pergularia pallida

Two new pregnane ester glycosides designated as pallidine and pallidinine have been isolated from the dried twigs of Pergularia pallida. Chemical and spectroscopic evidences are consistent with the structure 12,20-di-O-benzoyl sarcostin-3-O-β-d-oleandroside and 12,20-di-O-benzoyl-sarcostin-3-O-β-d-cymaropyranosyl(1 → 4)-β-d-oleandropyranoside for pallidine and pallidinine respectively.     

Synthesis of O-β-d-mannopyranosyl-(1→4)-O-α-l-rhamnopyranosyl-(1→3)-d-galactopyranose,the trisaccharide repeating-unit of the O-specific polysaccharide from Salmonella anatum

Glycosylation of 1,2:5,6-di-O-isopropylidene-α-d-galactofuranose with 2,3-di-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl)-α-l-rhamnopyranosyl bromide, followed by removal of the protecting groups, gave O-β-d-mannopyranosyl-(1→4)-O-α-l-rhamnopyranosyl-(1→3)-d-galactose, which is the trisaccharide repeating-unit of the O-specific polysaccharide chain of the lipopolysaccharide from Salmonella anatum. The formation of the β-d-mannopyranosyl linkage was achieved by a glucose-mannose conversion via stereoselective reduction of the corresponding oxo-disaccharide.     

A pregnane ester and its glycoside from Orthenthera viminea

A new pregnane ester named ornogenin and its diglycoside designated as ornine were isolated from the dried twigs of Orthenthera viminea. On the basis of chemical and spectroscopic evidence, their structures were established as 12,20-di-O-cinnamoyl-sarcostin and 12,20-di-O-cinnamoyl-sarcostin-3-O-α-L-oleandropyranosyl(1 → 4)-O-β-D-cymaropyranoside, respectively.     

The 13C-n.m.r. spectra of peracetylated cello-oligosaccharides

The reaction of 1,4-anhydro-2-deoxy-5,6-O-isopropylidene-d-arabino-hex-1-enitol (1) with m-chloroperbenzoic acid in ethanol gives 2,3-unsaturated ethyl glycosides together with saturated ethyl glycosides formed by trans-ring opening of 1,2-epoxide intermediates. Similar results are obtained on peroxidation of 1,4-anhydro-2-deoxy-3-O-(2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl)-5,6-O-isopropylidene-d-arabino-hex-1-enitol (2). Products resulting from osmylation of 1 and 2 and cleavage of the osmate esters are also described. 2-Deoxy derivatives are prepared from 1 and 2 by methoxymercuration-demercuration and also by reduction of 2-bromo-2-deoxy derivatives obtained by ethoxybromination.     

Synthesis of oligosaccharide fragments of mannan from <Emphasis Type="Italic">Candida albicans</Emphasis> cell wall and their BSA conjugates

3-Aminopropyl glycosides of α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→2)-α-D-mannopyranose, α-D-mannopyranosyl-(1→3)-α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→2)-α-D-mannopyranose, and α-D-mannopyranosyl-(1→2)-[α-D-mannopyranosyl-(1→3)]-α-D-mannopyranosyl-(1→2)-α-D-mannopyranosyl-(1→2)-α-D-mannopyranose were efficiently synthesized starting from ethyl 2-O-acetyl(benzoyl)-3,4,6-tri-O-benzyl-1-thio-α-D-mannopyranoside, ethyl 4,6-di-O-benzyl-2-O-benzoyl-1-thio-α-D-mannopyranoside, ethyl 4,6-di-O-benzyl-2,3-di-O-benzoyl-1-thio-α-D-mannopyranoside, and 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl bromide. The oligosaccharide chains synthesized correspond to the three structural types of side chains of mannan from Candida albicans cell wall. A conjugate of the third pentasaccharide with bovine serum albumin was prepared using the squarate method.     

A synthesis of psi-cytidine

2-O-Benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-, 4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-, and 2-O-benzoyl-3,4,6-tri-O-benzyl-α-d-galactopyranosyl chloride were converted into the corresponding 2,2,2-trifluoroethanesulfonates, and these were treated with allyl 2-O-benzoyl-3,6-di-O-benzyl-α-d-galactopyranoside, to give allyl 2-O-benzoyl-4-O-[2-O-benzoyl-3,6-di-O-benzyl-4-O-(chloroacetyl)-β-d-galactopyranosyl]-3,6-di-O-benzyl- α-d-galactopyranoside (26; 41% yield), allyl 4-O-(4-O-acetyl-2-O-benzoyl-3,6-di-O-benzyl-β-d-galactopyranosyl)-2-O-benzoyl-3,6-di-O-benzyl- α-d-galactopyranoside (27; 62% yield), and allyl 2-O-benzoyl-4-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-d-galactopyranosyl)-3,6-di-O-benzyl-α-d-galactopyranoside (28; 65% yield). All disaccharides were free from their α anomers. Disaccharides 26 and 27 were found to be base-sensitive, and were de-esterified by KCN in aqueous ethanol, and debenzylated with H₂-Pd. Attempts to produce (1→4)-β-d-galactopyranosides from the coupling of a number of fully esterified d-galactopyranosyl sulfonates to allyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside were unsuccessful.     

Flavonol triglycosides from Magnolia utilis

Three undescribed flavonol triglycosides, rhamnetin-3-O-α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-β-d-glucopyranoside (champaluangoside A), rhamnetin-3-O-α-l-rhamnopyranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→6)]-β-d-galactopyranoside (champaluangoside B) and rhamnocitrin-3-O-α-l-rhamnopyranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→6)]-β-d-glucopyranoside (champaluangoside C), were isolated from Magnolia utilis in addition to eleven known compounds; quercetrin-3-O-α-l-rhamnopyranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→6)]-β-d-glucopyranoside, oxytroflavoside G, magnoloside A, magnoloside M, magnoloside D, manglieside A, manglieside B, 1,2-di-O-β-d-glucopyranosyl-4-allylbebzene, syringrin, benzyl β-d-allopyranoside and (+)-syringaresinol-O-β-d-glucopyranoside. The structure elucidation of these compounds was based on analyses of physical and spectroscopic data.     

The assembly of oligosaccharides from “standardized intermediates”: β-(1→3)-linked oligomers of d-galactose

Several 2-O-benzoyl-4,6-di-O-benzyl-3-O-R-α-d-galactopyranosyl chlorides, designed as general precursors of β-linked, interior d-galactopyranosyl residues in oligosaccharides, were tested in a sequential synthesis of the galactotriose β-d-Galp-(1→3)-β-d-Galp-(1→3)-d-Gal (19). The chlorides having R = tetrahydro-2-pyranyl and tert-butyldimethylsilyl gave excellent results whereas those having = 3-benzoylpropionyl and chloroacetyl were unsatisfactory. An activated disaccharide block (17), having R = 2,3-di-O-benzoyl-4,6-di-O-benzyl-β-d-galactopyranosyl, was also prepared and tested as a glycosyl donor. The coupling of 17 to 1-propenyl 2-O-benzoyl-4,6-di-O-benzyl-α-d-galactopyranoside (14), in the molar ratio 1.13:1, gave 64% of a trisaccharide derivative (18) that could be converted into 19. This latter synthesis of 19 is efficient because all three galactose units are derived from 14 or its immediate precursor.     

Triterpenoid saponins from the bark of Zizyphus joazeiro

Three new triterpenoid saponins were isolated from the barks of Zizyphus joazeiro and characterized as jujubogenin 3-O-α-l-arabinofuranosyl-(1 → 2)-[β-d-glucopyranosyl(1 → 3)]-α-l-arabinopyranoside, its 4?-O-sulphate and 3″,4?-di-O-sulphate, respectively. FAB-MS was useful in providing information on the molecular weight of the complex oligoglycoside sulphates.     

Synthesis of three oligosaccharides that form part of the complex type of carbohydrate moiety of glycoproteins

Silver trifluoromethanesulfonate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-phthalimido-β-d-glucopyranosyl bromide with benzyl 3,6-di-O-benzyl-α-d-mannopyranoside and benzyl 3,4-di-O-benzyl-α-d-mannopyranoside gave the protected 2,4- and 2,6-linked trisaccharides in yields of 54 and 32%, respectively. After exchanging the 2-deoxy-2-phthalimido groups for 2-acetamido-2-deoxy groups and de-blocking, the trisaccharides 2,4-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-mannose and 2,6-di-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-d-mannose were obtained. Similar condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d-glucopyranosyl bromide with benzyl 3,4-di-O-benzyl-α-d-mannopyranoside gave a pentasaccharide derivative in 52% yield. After transformations analogous to those applied to the trisaccharides, 2,6-di-O-[β-d-galactopyranosyl-(1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)]-d-mannose was obtained.