Debenzylation of carbohydrate benzyl ethers and benzyl glycosides via free-radical bromination

The dealkylation of benzylated carbohydrates by free-radical bromination and hydrolysis has been further examined. Free-radical bromination of methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranoside (1) methyl 2,3-di-O-benzyl-α-D-glucopyranoside (2) 6-O-benzyl-3,5-O-benzylidene-1,2-O-isopropylidene-α-D-glucofuranose (4) and 6-O-benzyl-D-glucose (3) appears to be quantitative. Spectroscopic evidence of a CBr bond indicates that an α-bromobenzyl ether is the product. Alkaline hydrolysis yielded methyl α-D-glucopyranoside from 1 and 2 and D-glucose from 3 and 4. A benzyl group present as an aglycon could be removed in the same way. Reaction of benzyl α-D-glucopyranoside tetraacetate (6) with bromine and chlorine under free-radical conditions and examination of the products by t.l.c. and i.r. spectrophotometry indicated that the first product was an α-halobenzyl glycoside and that the aglycon could be displaced by Br^- or Cl^- to form the tetra-O-acetyl-D-glucopyranosyl halide, undoubtedly with anomerization. Treatment of the mixture of products with moist ether and silver carbonate yielded only 2,3,4,6-tetra-O-acetyl-D-glucopyranose.     

Nitrous acid deamination of methylated amino-oligosaccharide glycosides

G.l.c.-mass spectrometry has been used to characterize the products of N-deacetylation-nitrous acid deamination of per-O-methylated derivatives (8–11) of methyl 2-acetamido-2-deoxy-3-O-β-D-galactopyranosyl-α-D-glucopyranoside(1), methyl (2) and benzyl (3) 2-acetamido-2-deoxy-4-O-β-D-galactopyranosyl-β-D-glucopyranosides, and methyl 2-acetamido-2-deoxy-6-O-β-D-galactopyranosyl-α-D-glucopyranoside (4). 2,5-Anhydrohexoses have been converted into alditol trideuteriomethyl ethers, alditol acetates, and aldononitriles. The importance of side reactions that lead to the formation of 2-deoxy-2-C-formylpentofuranosides is discussed.     

Synthesis of methyl (or propyl) 2-acetamido-2-deoxy-α-D-glucopyranoside 6-(α-D-glucopyranosyl phosphate) and derivatives for the study of the phosphoric ester linkage in the Micrococcus lysodeikticus cell-wall

Methyl 2-acetamido-3-O-allyl-2-deoxy-4-O-methyl-α-D-glucopyranoside, methyl 2-acetamido-2-deoxy-4-O-methyl-α-D-glucopyranoside, and methyl 2-acetamido-3,4-di-O-allyl-2-deoxy-α-D-glucopyranoside, prepared from methyl 2-acetamido-2-deoxy-α-D-glucopyranoside, were coupled with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl phosphate (13), to give the phosphoric esters methyl 2-acetamido-3-O-allyl-2-deoxy-4-O-methyl-α-D-glucopyranoside 6-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl phosphate) (16), methyl 2-acetamido-2-deoxy-4-O-methyl-α-D-glucopyranoside 6-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl phosphate) (23), and methyl 2-acetamido-3,4-di-O-allyl-2-deoxy-α-D-glucopyranoside 6-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl phosphate) (17). Compound 13 was prepared from penta-O-acetyl-β-D-glucopyranose by the phosphoric acid procedure, or by acetylation of α-D-glucopyranosyl phosphate. Removal of the allyl groups from 16 and 17 gave 23 and methyl 2-acetamido-2-deoxy-α-D-glucopyranoside 6-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl phosphate) (19), respectively. O-Deacetylation of 23 gave methyl 2-acetamido-2-deoxy-4-O-methyl-α-D-glucopyranoside 6-(α-D-glucopyranosyl phosphate) (26) and O-deacetylation of 19 gave methyl 2-acetamido-2-deoxy-α-D-glucopyranoside 6-(α-D-glucopyranosyl phosphate) (24). Propyl 2-acetamido-2-deoxy-α-D-glucopyranoside 6-(α-D-glucopyranosyl phosphate) (25) was prepared by coupling 13 with allyl 2-acetamido-3,4-di-O-benzyl-2-deoxy-α-D-glucopyranoside, followed by catalytic hydrogenation of the product to give the propyl glycoside, which was then O-deacetylated. Compounds 24, 25, and 26 are being employed in structural studies of the Micrococcus lysodeikticus cell-wall.     

Flavonoids and phenolic acids from the aerial parts of Alyssum alyssoides L. (Brassicaceae)

Two phenolic acids (1 and 2) and seven flavonoids (3–9) were isolated from the aerial parts of Alyssum alyssoides (Brassicaceae). All these compounds (1–9) were isolated from this particular species for the first time. Their structures were identified, on the basis of MS and NMR spectra as: p-hydroxy-benzoic acid (1), 3-methoxy-4-hydroxybenzoic acid (vanillic acid) (2), kaempferol 3-O-β-D-glucopyranoside (astragalin) (3), kaempferol 3-O-(6″-α-L-rhamnopyranosyl)-β-D-glucopyranoside (nicotiflorin) (4), quercetin 3-O-β-D-glucopyranoside (isoquercetin) (5), quercetin 3-O-β-D-galactopyranoside (hyperoside) (6), isorhamnetin 3-O-β-D-glucopyranoside (7), isorhamnetin 3-O-β-D-galactopyranoside (8) and isorhamnetin 3-O-(6″-α-L-rhamnopyranosyl)-β-D-glucopyranoside (narcissin) (9). The chemotaxonomic significance of these compounds was summarized.     

Glycosidation at C-4 of 2-acetamido-2-deoxy-D-glucopyranose derivatives by koenigs-knorr type condensations

The condensation of 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl bromide and 2,3,4,6-tetra-O-benzyl-D-mannopyranosyl chloride with benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside (1), under Koenigs-Knorr conditions, gave the fully benzylated derivatives of benzyl 2-acetamido-2-deoxy-4-O-α-D-glucopyranosyl-α-D-glucopyranoside, benzyl 2-acetamido-2-deoxy-4-O-β-D-glucopyranosyl-α-D-glucopyranoside, and benzyl 2-acetamido-2-deoxy-4-O-α-D-mannopyranosyl-α-D-glucopyranoside. Three further compounds, namely, benzyl 2-acetamido-3-O-benzyl-2-deoxy-6-O-(2,3,4,6-tetra-O-benzyl-D-glucopyranosyl)-α-D-glucopyranoside, benzyl 2-acetamido-3-O-benzyl-2-deoxy-6-O-(2,3,4,6-tetra-O-benzyl-D)-mannopyranosyl)-α-D-glucopyranoside, and benzyl 2-acetamido-3-O-benzyl-2-deoxy-4,6-di-O-(2,3,4,6-tetra-O-benzyl-D-mannopyranosyl)-α-D-glucopyranoside, were formed by reaction of the respective glycosyl halide with benzyl 2-acetamido-3-O-benzyl-2-deoxy-α-D-glucopyranoside present as contaminant in 1.     

Synthèse des 2-acé-tamido-2-désoxy-6-O-α-et β-D-xylopyranosyl-α-D-glucopyranose

2-Acetamido-2- deoxy-6-O-, -xylopyranosyl-O-D-glucopyranose has been synthesized in crystalline form by condensation of 2,3,4-tri-O-acetyl-α-D-xylopyranosyl chloride (1) with benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-β-D-glucopyranoside (2), followed by O-deacetylation and catalytic hydrogenation. Condensation of 2 with 2,3,4-tri-O-chlorosulfonyl-β-D-xylopyranosyl chloride, followed by dechlorosulfonylation and acetylation, gave benzyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-(2,3,4-tri-O-acetyl-α-D-xylopyranosyl)β-D-glucopyranoside in crystalline form. O-Deacetylation, followed by catalytic hydrogenation, gave 2-acetamido-2-deoxy-6-O-α-D-xylopyranosyl-α-D-glucopyranose in crystalline form.     

Synthesis and properties of 2,3,4,6-tetra-O-benzyl-1-O-(N-benzyloxycarbonyldipeptidyl)-α- and -β-D-glucopyranoses and 1-O-dipeptidyl-D-glucopyranoses. Piperazinedione formation from 1-O-dipeptidyl-D-glucopyranoses by intramolecular aminolysis

2,3,4,6-Tetra-O-benzyl-1-O-(N-benzyloxycarbonyldipeptidyl)-D-glucopyranoses (1–5) were synthesized from 2,3,4,6-tetra-O-benzyl-α-D-glucopyranose and pentachlorophenyl esters of N-benzyloxycarbonyldipeptides in the presence of imidazole; the anomeric mixtures were resolved and the α and β anomers were characterized. Catalytic hydrogenation of the β anomers of 1–3, having aglycon groups containing aliphatic amino acid residues, afforded the corresponding 1-O-dipeptidyl-β-D-glucopyranoses, which were characterized as the mono-oxalates 6–8; 6 and 7 were converted into the N-acetyl derivatives 9 and 10, which were also prepared by definitive methods. Hydrogenolysis of the β anomers of 4 and 5, having aglycon groups containing Phe-Gly and Gly-Phe residues, led to intramolecular aminolysis with scission of the glycosidic ester bond to give 3-benzylpiperazine-2,5-dione and D-glucose. Selective N-deprotection of 5β afforded 2,3,4,6-tetra-O-benzyl-1-O-(glycyl-DL-phenylalanyl)-β-D-glucopyranose (13β), and complete deprotection of 5α gave 1-O-(glycyl-DL-phenylalanyl)-α-D-glucopyranose (14) as the preponderant products; in both cases, intramolecular cyclisation of the aglycon group was a minor reaction. The results suggest that the balance between the formation of free D-glucosyl ester and the respective piperazinedione derivative depends primarily upon the nature and the sequence of the amino acids involved, and to a lesser extent upon the nature of substituents and the anomeric configuration of the sugar component.     

The action of Bacillus subtilis liquefying amylase on 6-deoxy-6-iodoamylose

Benzyl 2-acetamido-2-deoxy-3-O-β-D-galactopyranosyl-α-D-glucopyranoside (1) was chosen as a model bioside to develop a standard procedure for the selective cleavage of glycosidic linkages in polysaccharides containing 2-amino-2-deoxyhexose residues. Treatment of 1 with hydrazine in the presence of hydrazine sulphate resulted in quantitative N-deacetylation with the formation of benzyl 2-amino-2-deoxy-3-O-β-D-galactopyranosyl-α-D-glucopyranoside (2). The galactosyl glycosidic linkage in 2 could be selectively cleaved by acid hydrolysis. Oxidation of 2 with periodate destroyed the galactose residue. Treatment of 2 with nitrous acid cleaved the 2-amino-2-deoxy-D-glucosyl linkage to give 2,5-anhydro-3-O-β-D-galactopyranosyl-D-mannose (3) and benzyl alcohol.     

A 24β-ethyl-Δ7-steryl glucopyranoside from Cucurbita pepo seeds

In the seeds of Cucurbita pepo three closely related 24-ethyl-Δ⁷-steryl glucosides were identified by hydrolytic studies and spectral analysis as spinasteryl-β-D-glucopyranoside, the new 3-O-(β-D-glucopyranosyl)-24β-ethyl-5α-cholesta-7,25(27)-dien-3β-ol and the corresponding Δ^22E,25,(27)-trienol. Except for its occurrence in cucumber seeds the latter is so far unknown as a natural product.     

Chromone acyl glucosides and an ayanin glucoside from Dasiphora parvifolia

Two new chromone acyl glucosides, 5-hydroxy-7-O-(6-O-p-cis-coumaroyl-β-D-glucopyranosyl)-chromone (1) and 5-hydroxy-7-O-(6-O-p-trans-coumaroyl-β-D-glucopyranosyl)-chromone (2), and a new flavonoid glucoside, ayanin 3′-O-β-D-glucopyranoside (3) were isolated from aerial parts of Dasiphora parvifolia, together with flavonoid glycosides (4–10), catechins (11, 12), and hydrolysable tannins (13, 14). The chemical structures of these compounds were elucidated on the basis of spectroscopic data. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and the hyaluronidase inhibitory activity of these compounds were evaluated.     

The synthesis of 4′,6′-diacetamido-4′,6′-dideoxycellobiose hexa-acetate from lactose

Reaction of methyl 4′,6′-di-O-mesyl-β-lactoside pentabenzoate (8), synthesised via the 4′,6′-O-benzylidene derivative (6), with sodium azide in hexamethylphosphoric triamide gave three products. In addition to the required 4′,6′-diazidocellobioside (9), an elimination product, methyl 4-O-(6-azido-2,3-di-O-benzoyl-4,6-dideoxy-α-L-threo-hex-4-enopyranosyl)-2,3,6-tri-O-benzoyl-β-D-glucopyranoside (12), and an unexpected product of interglycosidic cleavage, methyl 2,3,6-tri-O-benzoyl-β-D-glucopyranoside (13), were formed. The origin of the latter product is discussed. The diazide 9 was converted into 4′,6′-diacetamido-4′,6′-dideoxycellobiose hexa-acetate (16) by sequential debenzoylation, catalytic reduction, acetylation, and acetolysis.     

Angkorensides A and B – Two anti-inflammatory acyl glycosides from Gardenia angkorensis

Two new acyl glycosides, angkorensides A and B (1 and 2) together with twelve known compounds including hedyotol C 7″-O-β-D-glucopyranoside (3), proanthocyanidin A-1 (4), (-)-epicatechin (5), (+)-lyoniresinol 3α-O-β-D-glucopyranoside (6), kaempferol-3-O-β-D-galactopyranoside (7), cuneataside E (8), 4-hydroxyacetophenone 4-O-(6′-O-β-D-apiofuranosyl)-β-D-glucopyranoside (9), cinnamtannin B-1 (10), aesculitannin B (11), quercetin 3-O-rham-(1−6)-β-D-galactopyranoside (12), quercetin 3-O-β-D-galactopyranoside (13), and proanthocyanidin A-2 (14) have been unprecedentedly isolated from Gardenia angkorensis Pit. Angkorensides A and B (1 and 2) showed moderate anti-inflammatory inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 macrophages and the known compounds (4, 10-14) exhibited strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity.     

Synthesis,properties, and reactions of α- and β-D-glucopyranosyl esters of some tripeptides

The 2,3,4,6-tetra-O-benzyl-1-O-(N-benzyloxycarbonyltripeptidyl)-D-glucopyranoses 1, 8, and 13 were synthesised from 2,3,4,6-tetra-O-benzyl-α-D-glucopyranose and the active esters of the appropriate N-protected tripeptides (Gly-Gly-Gly-, L-Phe-Gly-Gly-, and Gly-Gly-L-Phe-) in the presence of imidazole; the anomeric mixtures were resolved and the α and β anomers characterised. The β anomer of 13, containing the L and D enantiomers (ratio ≈ 3:1) of Gly-Gly-Phe- as the aglycon, could be resolved by column chromatography into the pure isomeric forms. Catalytic hydrogenolysis of the β anomers, in the presence and absence of a strong acid, yielded the free 1-esters 2β, 9β, and 14β, which were characterised as the monooxalate or trifluoroacetate salts and as free bases. Similarly, the α anomers afforded 2α, 9α, and 14α, whereas omission of the strong acid led to accompanying 1→2 acyl migration, to give the 2-O-acyl derivatives. All of the compounds prepared were converted into the N-acetyl and/or peracetylated derivatives. The 1-esters 2β and 9β, both in the charged and uncharged form, and the trifluoroacetate salt of 14β, are susceptible to cleavage by β-D-glucosidase; the enzyme had no effect on the uncharged form of 14β. This difference between 14β and its salt is discussed in conformational terms.     

A new bicyclic sesquiterpenoid from Merremia yunnanensis

A new sesquiterpenoid, 1α,4β,8β,9β-eudesmane-tetrol-1-O-β-D-glucopyranoside (1), together with nine known compounds (2–10), were isolated from Merremia yunnanensis. The structures of these compounds were elucidated by spectroscopic methods and compared to data in the literature. All these compounds (1–10) were firstly isolated from this plant, and compounds 3, 5, 7, and 10 were reported from the Merremia genus for the first time. The significance of the chemotaxonomy for these compounds is described herein.     

Unsaturated sugars. I. Decarboxylative elimination of methyl 2,3-di-O-benzyl-alpha-D-glucopyranosiduronic acid to methyl 2,3-di-O-benzyl-4-deoxy-beta-L-threo-pent-4-enopyranoside

Decarboxylative elimination of methyl 2,3-di-O-benzyl-α-D-glucopyranosiduronic acid (1) with N,N-dimethylformamide dineopentyl acetal in N,N-dimethylformamide gave methyl 2,3-di-O-benzyl-4-deoxy-β-L-threo-pent-4-enopyranoside (3). Debenzylation of 3 was effected with sodium in liquid ammonia to give methyl 4-deoxy-β-L-threo-pent-4-enopyranoside (4). Hydrogenation of 3 catalyzed by palladium-on-barium sulfate afforded methyl 2,3-di-O-benzyl-4-deoxy-β-L-threo-pentopyranoside (5), whereas hydrogenation of 3 over palladium-on-carbon gave methyl 4-deoxy-β-L-threo-pentopyranoside (6). An improved preparation of methyl 4,6-O-benzylidene-α-D-glucopyranoside is also described.     

Two New Sesquiterpenoid Glucosides from the Aerial Parts of Saussurea involucrate

Two new sesqulterpenoid glucosides, namely α-hydroxycostic acid 6-β-D-glucopyranoside （compound 1） and 11 βH-11,13-dlhydrodehydrocostuslactone 8α-O-（6＇-acetyl）-β-D-glucopyranoside （compound 2）, along with 11 known sesqulterpenoids （compounds 3-13） were isolated from the aerial parts of Saussurea involucrate （Kar. et Kir.） Sch.- BIp. The structures of the new sesquiterpenoid glucosides were established by one- and two-dimensional nuclear magnetic resonance and mass spectrometry analysis.     

The structures of amentoflavone glycosides isolated from Psilotum nudum

On the basis of new spectroscopic evidence, structures are proposed for three amentoflavone glycosides and an apigenin di-C-glycoside previously isolated from Psilotum nudum. The major glycoside is identified as the 7,4′,4′“-tri-O-β-D-glucopyranoside, minor glycosides as the 4′,4′“-di-O-β-D-glucopyranoside and 7,4′“-di-O-β-D-glucopyranoside, and the apigenin di-C-glycoside as vicenin-2. The amentoflavone glucosides are all new natural products.     

Monoterpene indole alkaloids in Uncaria rhynchophlly (Miq.) Jacks chinensis and their chemotaxonomic significance

From the Uncaria rhynchophlly (Miq.) Jacks, twelve monoterpene indole alkaloids, such as harman (1), strictosamide (2), vincosidelactam (3), cadambine (4), 3α-dihydrocadambine (5), 7-epi-javaniside (6), rhynchophylline (7), isorhynchophylline (8), hirsutine (9), vincosamide-6′-O-β-D-glucopyranoside (10), vincosamide-11-O-β-D-glucopyranoside (11) and 2′-O-[β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]-11-hydroxyvincosamide (12) were isolated and identified. Structure elucidation of these compounds was performed on the basis of NMR spectroscopic data. Compounds 2, 5, 6, 10, 11 and 12 were obtained from this species for the first time. Chemotaxonomic significance of these compounds is described herein.     

5-Methyl ether flavone glucosides from the leaves of Bruguiera gymnorrhiza

Two new 5-methyl ether flavone glucosides (7,4′,5′-trihydroxy-5,3′-dimethoxyflavone 7-O-β-D-glucopyranoside and 7,4′-dihydroxy-5-methoxyflavone 7-O-β-D-glucopyranoside) were isolated from the leaves of Thai mangrove Bruguiera gymnorrhiza together with 7,3′,4′,5′-tetrahydroxy-5-methoxyflavone, 7,4′,5′-trihydroxy-5,3′-dimethoxyflavone, luteolin 5-methyl ether 7-O-β-D-glucopyranoside, 7,4′-dihydroxy-5,3′-dimethoxyflavone 7-O-β-D-glucopyranoside, quercetin 3-O-β-D-glucopyranoside, rutin, kaempferol 3-O-rutinoside, myricetin 3-O-rutinoside and an aryl-tetralin lignan rhamnoside. The structure of a lignan rhamnoside was found to be related to racemiside, an isolated compound from Cotoneaster racemiflora, and also discussed. Structure determinations were based on analyses of physical and spectroscopic data including 1D- and 2D-NMR.     

Oxazoline synthesis of 1,2-trans-2-acetamido-2-deoxyglycosides. Glycosylation with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-galactopyrano)-[2′,1′:4,5]-2-oxazoline

The glycosylating activity of 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-galactopyrano)-[2′,1′:4,5]-2-oxazoline has been tested in reaction with partially protected saccharides having free primary or secondary hydroxyl groups or with hydroxy amino acids. 3-O-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-galactopyranosyl)-N-benzyloxycarbonyl-L-serine benzyl ester (3), 6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-galactopyranose (5), p-nitrophenyl 2-acetamido-6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-2-deoxy-β-D-glucopyranoside (7), 6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-glucose (9), and 3-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-glucose (11) were synthesized in high yield.