Ken'ichi Takeo

Selective chemical modification of cyclomalto-oligosaccharides via tert-butyldimethylsilylation

Abstract Selective reaction of cyclomaltoheptaose and cyclomalto-octaose with tert-butylchlorodimethylsilane in N,N-dimethylformamide in the presence of imidazole gave the heptakis(6-O-tert-butyldimethylsilyl) (21) and octakis(6-O-tert-butyldimethylsilyl) (27) derivatives in yields of 70 and 67%, respectively. The twelve partially methylated regioisomers of cyclomalto-oligosaccharides, namely, hexakis(2- and 3-O-methyl, and 2,6- and 3,6-di-O-methyl)cyclomaltohexaoses, heptakis(2-, 3-, and 6-O-methyl and 2,3-, 2,6- and 3,6-di-O-methyl)cyclomaltoheptaoses, and octakis(6-O-methyl and 2,3-di-O-methyl)cyclomalto-octaoses, have been prepared crystalline by unambiguous routes using hexakis(6-O-tert-butyldimethylsilyl)cyclomaltohexaose (2), 21, and 27, respectively, as the key intermediates. The synthesis of several heptakis- and octakis-(6-substituted) derivatives of cyclomalto-heptaose and -octaose is also described.

An antitumor, branched (1 → 3)-β-d-glucan from a water extract of fruiting bodies of Cryptoporus volvatus

A water-soluble, (1-->6)-branched (1-->3)-beta-D-glucan (H-3-B) was isolated from a hot-water extract of the fruiting bodies of the fungus, Cryptoporus volvatus (Basidiomycetes). Enzymatic analysis using exo-(1-->3)-beta-D-glucanase and methylation analysis indicated that this polysaccharide has a main chain composed of beta-(1-->3)-linked D-glucopyranosyl residues, and single, beta-(1-->6)-linked D-glucopyranosyl residues attached as side chains to, on average, every fourth sugar residue of the main chain. This structure was confirmed by 13C NMR spectra of the glucan in Me2SO-d6. The weight-average molecular weight (Mw) of H-3-B was determined to be 44.0 x 10(4) by gel permeation chromatography equipped with a low-angle laser-light-scattering photometer. The electron microscopic observations showed that H-3-B and its sonicated sample (S-H-3-B, Mw = 13.7 x 10(4)) can be described as linear worm-like chains. The mass per unit length for native and sonicated H-3-B was determined to be 1750 and 1780 g mol-1 nm-1, respectively, from the contour lengths obtained by electron microscopy and the molecular weights. These values are in good agreement with that expected for the triple stranded structure. A sample denatured in 0.1 M NaOH and subsequently renatured by neutralization showed a mixture of linear and cyclic structures, and larger aggregates with less well-defined morphology. The H-3-B and S-H-3-B had antitumor activity against the Sarcoma 180 tumor.

Derivatives Of α-Cyclodextrin and the Synthesis of 6-O-α-D-Glucopyranosyl-α-Cyclodextrin

Abstract Regioselective silylation of α-cyclodextrin with tert-butyl-dimethylsilyl chloride in N, N-dimethylformamide in the presence of imidazole gave, in 75% yield, the hexakis(6-O-tert-butyldimethylsilyl) derivative 2, which was transformed into the hexakis(2,3-di-O-methyl, 6-O-methyl, 2,3-di-O-propyl, and 2,3-di-O-acetyl) derivatives. On methanesulfonylation and p-toluenesulfonylation, the hexakis(2,3-di-O-acetyl) derivative 16 afforded the hexakis(2,3-di-O-acetyl-6-O-methylsulfonyl 17 and 2,3-di-O-acetyl-6-O-p -tolylsulfonyl 18) derivatives, respectively. Nucleophilic displacement of 17 and 18 with iodide, bromide, chloride, and azide ions afforded the hexakis(6-deoxy-6-iodo 19, 6-bromo-6-deoxy, 6-chloro-6-deoxy, and 6-azido-6-deoxy) derivatives, respectively, of α-cyclodextrin dodeca-acetate. The hexakis (2, 3-di-O-acetyl-6-deoxy) derivative was prepared from 19. Selective glucosylation of 16 with 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide under catalysis by halide ion, followed by removal of...

Synthesis of the laminara-oligosaccharide methyl β-glycosides of dp 3-8

Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-α-d-glucopyranoside has been prepared in a good yield by anomerization of the corresponding β-thioglucoside with tin(IV) chloride and transformed, in three steps, into ethyl 2-O-benzoyl-4,6-O-benzylidene-1-thio-α-d-glucopyranoside (18). Chloroacetylation of 18, followed by treatment of the product with chlorine gave crystalline 2-O-benzoyl-4,6-O-benzylidene-3-O-chloroacetyl-β-d-glucopyranosyl chloride (20). This was coupled with methanol in the presence of silver carbonate-silver perchlorate and the product was O-dechloroacetylated to afford methyl 2-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (22). Silver triflate-promoted glucosylation of 18 with 20 gave a β-(1 → 3)-linked disaccharide derivative, reaction of which with chlorine yielded crystalline O-(2-O-benzoyl-4,6-O-benzylidene-3-O-chloroacetyl-β-d-glucopyranosyl)-(1 → 3)-2-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranosyl chloride (24). Likewise, condensation of 22 with 20 gave a β-(1 → 3)-linked disaccharide glycoside, which was partially deprotected to give methyl O-(2-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranosyl)-(1 → 3)-2-O-benzoyl-4,6-O-benzylidene-β-d-glucopyranoside (26). The methyl β-glycosides of a homologous series of (1 → 3)-linked β-d-gluco-oligosaccharides from the tri- to the octa-saccharide have been synthesized in a blockwise manner by using 22 and 26 as the glycosyl acceptors, 24 as the disaccharide donor, and silver triflate as the promoter.

A Structural Model for the Mechanisms of Elicitor Release from Fungal Cell Walls by Plant [beta]-1,3-Endoglucanase

The release of elicitor-active carbohydrates from fungal cell walls by [beta]-1,3-endoglucanase contained in host tissues has been implicated as one of the earliest processes in the interaction between soybean (Glycine max) and the fungal pathogen Phytophthora megasperma f. sp. glycinea leading to host defense responses such as phytoalexin production. The present study was conducted to evaluate the primary structure of the glucanase-released elicitor (RE). Gel-filtration chromatography of carbohydrates released from mycelial walls by purified soybean [beta]-1,3-endoglucanase resolved them into the four fractions (elicitor-active RE-I, -II, and -III and elicitor-inactive RE-IV). Sugar composition analysis indicated that all of the fractions were composed almost entirely of glucose. 1H- and 13C-nuclear magnetic resonance analysis indicated the presence of both [beta]-1,3- and [beta]-1,6-linkages for the elicitor-active RE-I, -II, and -III fractions and only [beta]-1,3 linkage for the elicitor-inactive RE-IV fraction. Methylation analysis and degradation studies employing [beta]-1,3-endo- and [beta]-1,3-exoglucanase further suggested that the basic structure of elicitor-active RE consists of [beta]-1,6-linked glucan backbone chains of various lengths with frequent side branches composed of [beta]-1,3-linked one or two glucose moieties. From these structural analyses of RE, a structural model of how RE is originally present in fungal cell walls and released by host [beta]-1,3-endoglucanase is also proposed.

Synthesis of lycotetraose

Abstract The title tetrasaccharide, namely, O -β- d -glucopyranosyl-(1→2)- O -[β- d -xylopyranosyl-(1→3)]- O -β- d -glucopyranosyl- (1→4)- d -galactose, has been synthesized by Koenigs-Knorr type of condensations in a stepwise manner by way of the preperation of the di- and tri-saccharide fragments, 4- O -β- d -glucopyranosyl- d -galactose (lycobiose) and O -β- d -glucopyranosyl-(1→2)- O -β- d -glucopyranosyl-(1→4)- d -galactose (lycotriose I), using benzyl 2,3,6-tri- O -benzyl-β- d -galactopyranoside as the starting glycosyl acceptor, and 2,3,4,6-tetra- and 2,4,6-tri- O -acetyl-3- O -allyl-α- d -glucopyranosyl bromide and 2,3,4-tri- O -benzoyl-α- d -xylopyranosyl bromide as the glycosyl donors.

Synthesis of methyl α- and β-maltotriosides and aryl β-maltotriosides

Abstract Reaction of β-maltotriose hendecaacetate with phosphorus pentachloride gave 2′,2″,3,3′,3″,4″,6,6′,6″,-nona- O -acetyl-(2)- O -trichloroacetyl-β-maltotriosyl chloride (2) which was isomerized into the corresponding α anomer (8) . Selective ammonolysis of 2 and 8 afforded the 2-hydroxy derivatives 3 and 9 , respectively; 3 was isomerized into the α anomer 9 . Methanolysis of 2 and 3 in the presence of pyridine and silver nitrate and subsequent deacetylation gave methyl α-maltotrioside. Likewise, methanolysis and O -deacetylation of 9 gave methyl β-maltotrioside which was identical with the compound prepared by the Koenigs—Knorr reaction of 2,2′,2″,3,3′,3″,4″,6,6′,6″-deca- O -acetyl-α-maltotriosyl bromide (12) with methanol followed by O -deacetylation. Several substituted phenyl β-glycosides of maltotriose were also obtained by condensation of phenols with 12 in an alkaline medium. Alkaline degradation of the o -chlorophenyl β-glycoside decaacetate readily gave a high yield of 1,6-anhydro-β-maltotriose.

Conformation of cyclic and linear (1 → 2)-β-d-glucans in aqueous solution

Abstract The conformations of cyclic (1 → 2)-β- d -glucan chains having degree of polymerization (dp) 17 to 24 were characterized by means of small-angle X-ray scattering and Monte Carlo simulation. The results indicate that cyclic (1 → 2)-β- d -glucan chains adopt the shape of a doughnut-like ring with a thickness of about 10 A for all the samples. The diameter of the annulus for the cyclic glucan having dp 21 is estimated to be only about 4–5 A. Two linear (1 → 2)-β- d -glucans possessing dp 19 and 21 prepared by acid hydrolysis of a cyclic glucan and subsequent fractionation showed different scattering profiles from those obtained for cyclic glucans having the corresponding dp. Although the Monte Carlo simulation does not completely reproduce the scattering profiles observed by small-angle X-ray scattering, linear (1 → 2)-β- d -glucans seem to possess a characteristic cylindrical shape with cross-sectional diameters of 11.8 and 13.2 A for linear glucans of dp 19 and 21, respectively.

Synthesis of 2- and 4-nitrophenyl β-glycosides of β-(1 → 4)-d-xylo-oligosaccharides of dp 2–4

2- and 4-Nitrophenyl β-d-xylopyranosides (4 and 5) were transformed, via dibutyltin oxide-mediated acylation, into the corresponding 2,3-di-O-benzoyl derivatives 11 and 15. Xylobiose and xylotriose were easily isolated by charcoal column chromatography from a commercially available material and converted into the di- and trisaccharide methyl 1-thio-β-glycosides 36 and 37. The 2- and 4-nitrophenyl β-glycosides of the β-(1 → 4)-d-xylo-oligosaccharides of dp 2–4 were synthesized by N-iodosuccinimide-silver triflate-promoted condensation using 11 and 15 as the glycosyl acceptors and ethyl 1-thio-β-d-xylopyranoside triacetate 16, 36, and 37 as the glycosyl donors. Also described are an improved preparation of 4 and 5, and the synthesis of 1-naphthyl β-d-xylopyranoside, as well as an alternative approach to the 2- and 4-nitrophenyl β-xylobiosides.

Chemical modification of methyl β-cellobioside

Abstract Treatment of methyl β-cellobioside (1) with α,α-dimethoxytoluene in N,N -dimethylformamide in the presence of p -toluenesulfonic acid gave a high yield of methyl 4′,6′- O -benzylidene-β-cellobioside (6) , which was transformed into methyl 2,3,2′,3′,4′,6′-hexa- O -acetyl-6- O-p -tolylsulfonyl- (4) and methyl 2,3,6,2′,3′,4′-hexa- O -acetyl-6′- O-p -tolylsulfonyl-β-cellobioside (5) . Several 6- and 6′-monosubstituted derivatives of 1 were synthesized by displacement reactions of 4 and 5 with various nucleophiles. Treatment of 4 and 5 with sodium methoxide gave methyl 3,6-anhydro- and methyl 3′,6′-anhydro-β-cellobioside, respectively. The synthesis and catalytic hydrogenation of the 5- and 5′-ene derivatives of 1 are described. Conversion of 1 into methyl 4- O -β- d -allopyranosyl-β- d -allopyranoside and methyl 4- O -β- d -amicetosyl-β- d -amicetoside was undertaken, using 6 as the key intermediate.