Synthesis of Star-Shaped Polymers via Coordination of Bipyridyl-Terminated Polyoxyethylene with Metal Ions

Abstract

This paper describes the synthesis of various star-shaped polymers by means of complexation of bipyridyl-terminated polyoxyethylene with Ru(II) ion. Three kinds of bipyridyl-terminated polyoxyethylenes of different molecular weights were prepared from the corresponding polyoxyethylene monomethyl ethers with narrow molecular weight distributions. Bipyridyl was found to be introduced quantitatively at the end of the polymers based on the results of UV spectra. The formation of a star-shaped polymer was carried out by the reaction of RuCl₃ with three equivalents of bipyridyl-terminated polyoxyethylene. The UV spectrum of the star-shaped polymer obtained supported the formation of a typical Ru(II) tris(bipyridyl) complex. From the results of GPC, the star-shaped polymer obtained had a higher molecular weight than the pre-polymer and showed a narrow molecular weight distribution. In the case of a Ni(II) or a Co(II) complex, however, the star-shaped polymer was found to be dissociated into three linear prepolymers under the conditions of GPC measurement.     

Convenient Method for Dehalogenation of Aryl Halides

Reductive dehalogenation of aryl halides was achieved using hydrogen and a palladium catalyst. By using deuterium gas, the deuterated arenes were readily prepared.     

Unusual annulation reaction of electron-deficient alkenes with enamines: an easy access to stereocontrolled 4-fluoroalkylated 3,4-dihydro-2H-pyrans

The reaction of β-fluoroalkylated α,β-unsaturated ketones with various enamines gave 4-fluoroalkylated 3,4-dihydro-2H-pyrans as a major product in good yields by a one-pot operation, and these products display the high diastereoselection just after single recrystallization. This unexpected result is rationalized by the unique reactivity of β-fluoroalkylated α,β-unsaturated ketones. As the synthetic application, 4-trifluoromethyl tetrahydropyran was synthesized in moderate isolated yield with high diastereoselectivity.     

Visco-elastic properties of reentrant nematic liquid crystalline mixtures

The visco-elastic properties for binary mixtures of 4-n -hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) are investigated in detail by a light scattering technique. The mixtures exhibit a reentrant nematic (RN) phase between the smectic A (SmA) and crystal phases in the range 22.0–29.5 wt % of 6OCB. The viscosity and the elastic constant increase with cooling in both the nematic and reentrant nematic phases. It is also found that the mixtures exhibit anomalously large values of viscosity and elastic constant near the phase transition, i.e. a pretransitional phenomenon can be observed. The activation energy for viscosity is smaller in the RN phase than in the ordinary nematic phase appearing at higher temperatures, while the normalized elastic constant (defined as the ratio of the elastic constant to the square of the dielectric anisotropy) is larger. Moreover, the visco-elastic behaviour depends on the specific time during which the sample has been kept in the SmA phase. These results confirm that the SmA phase has a strong influence on the formation of molecular aggregates, which plays an important role in the reentrant phenomenon of these systems.     

Synthetic Studies on Sialoglycoconjugates 60: α-Stereocontrolled,Glycoside Synthesis of Trimeric Sialic Acid with Galactose and Lactose Derivatives

Abstract

α-Stereocontrolled, glycoside synthesis of trimeric sialic acid is described toward a systematic approach to the synthesis of sialoglycoconjugates containing an α-sialyl-(2→8)-α-sialyl-(2→8)-sialic acid unit α-glycosidically linked to O-3 of a galactose residue in their oligosaccharide chains. Glycosylation of 2-(trimethylsilyl)ethyl 6-O-benzoyl-β-d-galactopyranoside (4) or 2-(trimethylsilyl)ethyl 2,3,6,2′,6′-penta-O-benzyl-β-lactoside (5), with methyl [phenyl 5-acetamido-8-O-[5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylono-1”, 9′-lactone)-4,7-di-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylono-1′, 9-lactone]-4,7-di-O-acetyl-3,5-dideoxy-2-thio-d-glycero-d-galacto-2-nonulopyranosid]onate (3), using N-iodosuccinimide-trifluoromethanesulfonic acid as a promoter, gave the corresponding α-glycosides 6 and 8, respectively. The glycosyl donor 3 was prepared from trimeric sialic acid by treatment with Amberlite IR-120 (H⁺) resin in methanol, O-acetylation, and subsequent replacement of the anomeric acetoxy group with phenylthio. Compounds 6 and 8 were converted into the per-O-acyl derivatives 7 and 9, respectively.     

Synthetic Studies on Sialoglycoconjugates 70: Synthesis of Sialyl and Sulfo Lewis × Analogs Containing a Ceramide or 2-(Tetradecyl)hexadecyl Residue

Abstract

Four sialyl and sulfo Le^x analogs containing glucose in place of N-acetylglucosamine, and a ceramide or 2-(tetradecyl)hexadecyl residue, have been synthesized. Condensation of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-O-(4-O-acetyl-2,6-diO-benzoyl-β-d-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-acetyl-α-L-fucopyranosyl)-(1→3)]-2,4-di-O-benzoyl-α-d-glucopyranosyl trichloroacetimidate (1) with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3, diol (2) or 2-(tetradecyl)-hexadecyl-1-ol (3) gave the corresponding β-glycosides 4 and 7. Compound 4 was converted into the ganglioside 6 via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and saponification of the methyl ester group. Hydrolysis of the O-acyl groups in 7 followed by saponification of the methyl ester, gave sialyl Le^x ganglioside analog 8 containing a branched fatty alkyl residue. On the other hand, glycosylation of O-(4-O-acetyl-2,6-di-O-benzoyl-3-O-levulinyl-β-d-galactopyranosyl)-(1→4)-[O-(2,3,4-tri-O-acetyl-α-L-fucopyranosyl)-(1→3)]-2,6-di-O-benzoyl-α-d-glucopyranosyl trichloroacetimidate (13), prepared from 2-(trimethylsilyl)ethyl O-(2,6-di-O-benzoyl-β-d-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)]-2,6-di-O-benzoyl-β-d-glucopyranoside (9) via selective 3-O-levulinylation, acetylation, removal of the 2-(trimethylsilyl)ethyl group, with 2 or 3, gave the desired β-glycosides 14 and 19. Selective reduction of the axido group in 14 followed by coupling with octadecanoic acid gave the ceramide derivative 16. Removal of the levulinyl group in 16 and 19, treatment with sulfur trioxide pyridine complex and subsequent hydrolysis of the protecting groups yielded the corresponding sulfo Le^x analogs 18 and 21.     

Synthetic Studies on Sialoglycoconjugates 12: Total Synthesis of Sialyl Neolactotetraosyl Ceramide

Abstract

Sialoglycoconjugates such as glycoproteins and glycolipids are present as components of cell memberanes and play important roles^1,2 in biological systems. Sialyl neolactotetrasyl ceramide (IV³NeuAcnLc₄Cer), a complex type of ganglioside, was isolated as the major ganglioside of human erythrocytes³ and was shown to be a receptor of that this glycolipid induces granulocytic differentiation of human premyelocytic leukemia cell.