Microwave-Assisted Heating Reactions of N-Acetylglucosamine (GlcNAc) in Sulfolane as a Method Generating 1,6-Anhydrosugars Consisting of Amino Monosaccharide Backbones.

The microwave-assisted heating reaction of N-acetyl glucosamine (GlcNAc) in sulfolane is described. The reaction produces two major products that are assignable to 1,6-anhydro-2-acetamido-2-deoxy-ß-d-glucopyranose (AGPNAc) and 1,6-anhydro-2-acetamido-2-deoxy-ß-d-glucofuranose (AGFNAc). In order to reveal a general feature of the system, the 3, 5, and 10 min reactions were performed at 140, 160, 180, 200, and 220 °C to clarify the time course changes in the conversion of GlcNAc and the yields of the two produced 1,6-anhydrosugars. Temperature is a crucial factor that significantly affects the conversion of GlcNAc. The yields of AGPNAc and AGFNAc are also drastically changed depending on the reaction conditions. The 5-min reaction at 200 °C is shown to be the optimal condition to generate the 1,6-anhydrosugars with a high efficiency in which AGPNAc and AGFNAc are produced in the yields of 21% and 44%, respectively. Consequently, the microwave-assisted heating reaction of GlcNAc in sulfolane is shown to be a simple and promising pathway to generate 1,6-anhydrosugars consisting of amino monosaccharide backbones, which have high potentials as raw materials leading to biological oligosaccharides and biomimetic polysaccharides.

Selective synthesis of 1,6-anhydro-ß-d-mannopyranose and -mannofuranose using microwave-assisted heating.

The dehydration of d-mannose and the demethanolization of methyl-α-d-mannopyranoside (MαMP) or methyl-α-d-mannofuranoside (MαMF) were examined using microwave-assisted heating for a 3-min irradiation at temperature from 120 to 280°C in ordinary or dry sulfolane without any catalyst. The microwave-assisted heating of MαMP and MαMF smoothly proceeded to selectively afford the anhydromannoses, 1,6-anhydro-ß-d-mannopyranose (AMP) and 1,6-anhydro-ß-d-mannofuranose (AMF), respectively, in high yields. For MαMP in ordinary sulfolane at 240°C, AMP was selectively obtained in the AMF:AMP ratio of 4:96, whereas AMF was the major product at the AMF:AMP ratio of 97:3 from MαMF in dry sulfolane at 220°C.

Synthesis, characterization, and lectin recognition of hyperbranched polysaccharide obtained from 1,6-anhydro-D-hexofuranose.

1,6-Anhydro-D-hexofuranoses, such as 1,6-anhydro-ß-D-glucofuranose (1), 1,6-anhydro-ß-D-mannofuranose (2), and 1,6-anhydro-α-D-galactofuranose (3), were polymerized using a thermally induced cationic catalyst in dry propylene carbonate to afford hyperbranched polysaccharides (poly1-3) with degrees of branching from 0.40 to 0.46. The weight-average molecular weights of poly1-3 measured by multiangle laser light scattering varied in the range from (1.02 to 5.84) × 10(4) g·mol(-1), which were significantly higher than those measured by size exclusion chromatography. The intrinsic viscosities ([η]) of poly1-3 were very low in the range from 4.9 to 7.4 mL·g(-1). The exponent (α) in the Mark-Houkwink-Sakurada equation ([η] = KM(α)) of the polymers was 0.20 to 0.33, which is <0.5. The steady shear flow of poly1-3 in an aqueous solution exhibited a Newtonian behavior with steady shear viscosities independent of the shear rate. These viscosity characteristics were attributed to the spherical structures of hyperbranched polysaccharides in an aqueous solution. Poly1-3 contained a high portion of terminal units of 31-43 mol % nonreducing D-hexopyranosyl and D-hexofuranosyl units, in which the D-hexofuranosyl units were 20-44 mol %. Moreover, poly1 and poly2 showed a strong interaction to Concanavalin A due to the cluster effect or multivalent effect of numerous nonreducing saccharide units on their surfaces with binding constants in the range from 1.7 × 10(4) to 2.7 × 10(5) M(-1).

Thermochemical transformation of glucose to 1,6-anhydroglucose in high-temperature steam.

An aqueous solution of glucose was reacted at temperatures from 200 to 400 degrees C under atmospheric pressure using a continuous flow reactor. For reaction temperatures above 300 degrees C, the liquid product yield was not sensitive to the temperature change; on the other hand, below 300 degrees C, it decreased rapidly with decreasing temperature. 1,6-Anhydro-beta-D-glucopyranose (AGP) and 1,6-anhydro-beta-D-glucofuranose (AGF) were the major components in the liquid product. The yields of AGP and AGF were 40% and 19%, respectively, at 360 degrees C and a feed rate of 0.5 mL/min. The optimum space time to produce AGP and AGF was about 0.2-0.4s under the present temperature conditions.

On the synthesis of protopine alkaloids.

For the synthesis of protopine alkaloids, we studied a reaction sequence based on a ring enlargement of indeno[2,1-a][3]benzazepines by a singlet oxygen oxygenation, followed by conversion of an amide carbonyl group of the resultant 10-membered keto-lactam to a methylene group, which is the last step for completion of the synthesis. The key substances, indeno[2,1-a][3]benzazepines, were prepared by Bischler-Napieralski cyclization of alkoxy-substituted 1-(2-bromobenzyl)-3-benzazepin-2-ones. Steric effects of the substituents in this synthesis were examined.

Polystyrene microgel amphiphiles with maltohexaose. Synthesis, characterization, and potential applications.

4-Vinylbenzyl maltohexaoside peracetate (1) was copolymerized with divinylbenzene (DVB) using 1-phenyl-1-(2',2',6',6'-tetramethyl-1'-piperidinyloxy)ethane (2) in m-xylene. The copolymerizations were performed at 138 degrees C for 20 h using the mole fraction of 1 in the total feed of 1 and DVB (F1: [1]/[1]+[DVB]) varying from 0.11 to 0.38, affording polymeric products in yields ranging from 32 to 40%. The characterizations by linear PS-calibrated size exclusion chromatography (SEC), dynamic laser light scattering (DLS) measurements, and 1H NMR spectroscopy indicated that the product was assignable to the cross-linked poly(4-vinylbenzyl maltohexaoside peracetate) particle which is able to produce stable solutions, i.e., the PSt microgel with acetyl maltohexaose, 3. The specific rotations ([alpha]D23, c = 1.0 CHCl3) of 3 ranged from +43.3 degrees to +85.6 degrees. The average molar masses determined by the static laser light scattering (SLS) measurement of 3, M(w,SLS)'s, were from 64,700 to 118,000, which were calculated using the respective refractive index increments, dn/dc's, ranging from 0.03387 to 0.08340. The apparent numbers of the 1, 2, and DVB units in 3, N1, N2, and N(DVB), which were estimated from the respective [alpha]D23 values, M(w,SLS)'s, and real yields, ranged from 22 to 35, from 7 to 26, and from 146 to 506, respectively. The deacetylation of 3 was achieved by treatment with sodium methoxide in dry 1,4-dioxane to produce the PSt microgel with maltohexaose as the hydrophilic segment, 4, as a white solid. The solubility of 4 in various solvents was examined, indicating that a hydrophilic property was effectively introduced. Notably, 4 gave clear solutions in the mixed solvent of 1,4-dioxane and H2O. The ability to solubilize fullerite (mixture of fullerenes, C60/C70 = ca. 9/1) in aqueous solutions was examined according to the literature method. Approximately, 100 mg of 4 (1.7 micromol) solubilizes 1.3 mg of fullerite (1.7 micromol).

Enantioseparation properties of (1-->6)-alpha-D-glucopyranan and (1-->6)-alpha-D-mannopyranan tris(phenylcarbamate)s as chiral stationary phases in HPLC.

Synthetic polysaccharides, (1-->6)-alpha-D-glucopyranan (3a) and (1-->6)-alpha-D-mannopyranan (3b), were prepared by the cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-beta-D-glucopyranose (1a) and 1,6-anhydro-2,3,4-O-6-allyl-beta-D-mannopyranose (1b), followed by the cleavage of the allyl ether linkage of 2,3,4-tri-O-allyl-(1-->6)-alpha-D-glucopyranan (2a) and 2,3,4-tri-O-allyl-(1-->6)-alpha-D-mannopyranan (2b), respectively. 2,3,4-Tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-glucopyranan (CSP-1 and CSP-2, respectively) and 2,3,4-tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-mannopyranan (CSP-3 and CSP-4, respectively) were prepared by the reaction of 3 with the corresponding 3,5-disubstituted phenylisocyanates and the chiral recognition abilities of CSP-1-4 as chiral stationary phases (CSPs) in high-performance liquid chromatography (HPLC) were evaluated. Racemic compounds such as trans-cyclopropanedicarboxylic acid dianilide (9), 1,2,2,2-tetraphenylethanol (10), flavanone (11), Tröger's base (12), benzoin (13), and cobalt(III) tris(acetylacetonate) (14) were efficiently resolved using CSP-1-4. For comparison among CSPs, the chiral recognition properties of the (1-->6)-alpha-D-glucopyranan CSPs were different from that of the (1-->6)-alpha-D-mannopyranan CSPs, and CSP-4 exhibited the highest chiral recognition ability among the CSPs. The resolution factors of 12 and 14 were 0.42 and 0.56 for CSP-1, 0.32 and 2.16 for CSP-2, 1.80 and 0.84 for CSP-3, and 2.31 and 8.26 for CSP-4, respectively.