Synthesis and chiroptical properties of optically active, regioregular oligothiophenes.

[reaction: see text] A series of regioregular oligothiophenes bearing chiral oxazoline residues have been synthesized in high yields by a stepwise synthesis using the Stille cross-coupling reaction. The chiroptical properties of the oligothiophenes up to the octamer were investigated with UV-visible and CD spectroscopies. The octamer showed split-type Cotton effects in chloroform as a good solvent in the presence of a poor solvent such as acetonitrile, while the lower molecular weight oligomers exhibited almost no induced CD.

First isolation and characterization of eight regioisomers for [60]fullerene-benzene bisadducts.

[reaction: see text]. The [2 + 2] cycloaddition between [60]fullerene and benzyne generated from 4,5-dimethoxyanthranilic acid (4) afforded bisadducts 5 along with the monoadduct. All of the eight possible regioisomers were first isolated by HPLC and then characterized on the basis of MS, NMR, UV-vis, and CD spectroscopies.

Polysaccharide-based chiral stationary phases for high-performance liquid chromatographic enantioseparation.

Recent developments of polysaccharide-based chiral stationary phases (CSPs) for the direct separation of enantiomers in high-performance liquid chromatography (HPLC) are mainly reviewed together with the results on mechanistic studies by means of chromatography, NMR and mass spectroscopies, and computational methods. Miscellaneous applications of polysaccharide derivatives to the newly developed, chiral dynamic high-performance liquid chromatography (DHPLC) for obtaining a nonracemic compound are also described.

Unusual solvent effects on chiroptical properties of an optically active regioregular polythiophene in solution.

The chiroptical properties of a novel, optically active regioregular poly[3-(4-((R)-4-ethyl-2-oxazolin-2-yl)phenyl)thiophene] (poly-1) were investigated in mixtures of a good solvent, chloroform, and a variety of poor solvents using CD spectroscopy. Most poor solvents induced CD on poly-1 with similar Cotton effects, while acetonitrile and nitromethane caused dramatic changes in the Cotton effects of poly-1.

Chiral recognition of cellulose tris(5-fluoro-2-methylpheylcarbamate) toward (R)- and (S)-1, 1'-bi-2-naphthol detected by negative ion fast-atom bombardment mass spectrometry

Chiral recognition between cellulose tris(5-fluoro-2-methylphenylcarbamate) (MW > 120,000) as a host compound and (R,S)-1,1'-binaphthol (MW 286) as a guest compound was investigated by fast-atom bombardment mass spectrometry (FAB-MS). The use of negative ion FAB-MS made it possible to obtain a very simple mass spectrum of the guest compound with a high signal-to-noise ratio. Additionally, when nitrophenyl octyl ether, which has no OH group, was utilized as matrix, chiral recognition between the host and the guest compounds was unequivocally detected. Copyright 1999 John Wiley & Sons, Ltd.

Enantioseparation of atropisomeric 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate in capillary electrophoresis by using di- and oligosaccharides as chiral selectors: di- and oligosaccharide chiral selectors in capillary electrophoresis.

Twelve different disaccharides and a series of noncyclic malto- and cello-oligosaccharides were used as chiral selectors in capillary electrophoresis (CE). Most saccharides resolved the enantiomers of atropisomeric 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BDHP) depending on the type (alpha or beta) and position of the linkage between monosaccharides. The effect of chain length of malto- and cello-oligosaccharides on enantioseparation of BDHP was also investigated. The nature of cations in background electrolytes affected significantly the separation of BDHP enantiomers.

Enantioseparation using selected polysaccharides as chiral buffer additives in capillary electrophoresis.

Selected water-soluble, native polysaccharides--such as amylose, laminaran, pullulan--and derivatized polysaccharides--methyl cellulose, hydroxypropyl cellulose, and carboxymethyl amylose sodium salt (CM-Am)--were investigated as chiral selectors in capillary electrophoresis. Effects of degree of polymerization and concentration of amylose on the separation of enantiomers of 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BDHP) and a chiral cardiovascular drug cis-diltiazem were also studied. Pullulan and amyloses used in this study showed the same migration order for enantiomers of BDHP. In contrast, the migration order of BDHP enantiomers for cellulose derivatives and luminaran as well as with beta-cyclodextrin was opposite to that for amylose and pullulan. The enantioseparation of several chiral drugs was also performed using high-molecular-mass amylose (Am-4900) and CM-Am.

Preparation of silica gel-bonded amylose through enzyme-catalyzed polymerization and chiral recognition ability of its phenylcarbamate derivative in HPLC.

Amylose was prepared by enzymatic polymerization of alpha-D-glucose 1-phosphate dipotassium catalyzed by a phosphorylase using two kinds of the primers derived from maltopentaose, and then it was chemically bonded to silica gel to be used as a chiral stationary phase (CSP) in high-performance liquid chromatography. In method I, maltopentaose was first lactonized and allowed to react with (3-aminopropyl)triethoxysilane to form an amide bond. Amylose chains with a desired chain length and a narrow molecular weight distribution were then constructed by the enzymatic polymerization. The resulting amylose bearing a trialkoxysilyl group at the terminal was allowed to react with silica gel for immobilization. In method II, maltopentaose was first oxidized to form a potassium gluconate at the reducing terminal. After the enzymatic polymerization was performed with the potassium gluconate, the amylose end was lactonized to be immobilized to 3-aminopropyl-silanized silica gel through amide bond formation. Two amylose-conjugated silica gels thus obtained were treated with a large excess of 3,5-dimethylphenyl isocyanate to convert hydroxy groups of amylose to corresponding carbamate residues. The CSP derived through method II was superior in chiral recognition to the CSP derived from method I and showed better resolving power and higher durability against solvents such as tetrahydrofuran compared with a coated-type CSP. Influences of degree of polymerization of amylose, the spacer length between amylose and silica gel, and mobile phase compositions on chiral recognition were investigated.

High performance liquid chromatography enantioseparation of chiral pharmaceuticals using tris(chloro-methylphenylcarbamate)s of cellulose.

Chiral recognition abilities of a recently developed new type of cellulose phenylcarbamates were studied. These chiral stationary phases (CSPs) simultaneously contain both electron-withdrawing (Cl) and electron-donating (CH3) substituents on the phenyl moiety. Chiral pharmaceuticals which belong to the various pharmacological groups (sedatives, hypnotics, anticonvulsants, Ca2+ channel blockers, beta-blockers, antitusives, antihystaminics, choleretics, diuretics, antimycotics, etc) were resolved to enantiomers. These new CSPs sometimes exhibit alternative chiral recognition ability to that most successful commercially available cellulosic CSP Chiralcel-OD and can be used as a good complement to it in analytical and preparative scale enantioseparations.

Computational studies on chiral discrimination mechanism of cellulose trisphenylcarbamate.

The calculation of interaction energies between cellulose trisphenylcarbamate (CTPC) and enantiomers of (+/-)-trans-stilbene oxide (1) and (+/-)-trans-1,2-diphenylcyclopropane (2) was performed using QUANTA/CHARMm and MOLECULAR INTERACTION programs to gain an insight into the chiral recognition mechanism of phenylcarbamate derivatives of cellulose. The structure of CTPC was optimized with the CHARMm force field based on the proposed structure of CTPC by X-ray analysis. In chromatographic enantioseparation on CTPC, 1 was completely resolved (alpha = 1.46) and the (R,R)-(+)-isomer eluted first followed by the (S,S)-(-)-isomer, but 2 was not resolved (alpha approximately 1). The results of calculation of interaction energies between CTPC and the enantiomers 1 suggested that the most important adsorbing site of CTPC for 1 may be the NH protons of the carbamate moieties at the 3-position of glucose units, and the (S,S)-(-)-isomer of 1 may interact more closely than the (R,R)-(+)-isomer with CTPC. In contrast, there was little difference in the minimum interaction energies between the enantiomers 2. These calculations agreed with the observed results for the chromatographic resolution on CTPC.

Immobilization of human thrombomodulin onto poly(ether urethane urea) for developing antithrombogenic blood-contacting materials.

Thrombomodulin (TM) is a newly described endothelial cell-associated protein that functions as a potent natural anticoagulant by converting thrombin from a procoagulant protease to an anticoagulant. In this study, focussing on the application of TM for biomedical materials, recombinant human TM (hTM) was immobilized onto the polymers for medical use, and the evaluation of their antithrombogenicity and the interaction with platelets were investigated. As the base polymer for immobilization reaction, poly(ether urethane urea) (PEUU), which was reported to have good blood compatibility, was used. hTM-immobilized PEUU showed superior antithrombogenic activity, such as the prolongation of plasma recalcification time and the inhibition of thrombin-induced platelet aggregation, though the amount of immobilized hTM was very small (i.e. less than 1 microgram/cm2). Platelet adhesions onto hTM-immobilized PEUU were not observed. These results show that the immobilization of hTM does not change the native good blood compatibility of PEUU, but provides excellent anticoagulant activity.

Affinity gel electrophoresis of nucleic acids. Nucleobase-selective separation of DNA and RNA on agarose-poly(9-vinyladenine) conjugated gel.

Poly(9-vinyladenine) (PVAd) was immobilized within an agarose gel matrix to produce a novel affinity gel for the base-specific separation of nucleic acids by electrophoresis. The shape (single- or double-stranded) and base content of nucleic acids were specifically recognized by the affinity gel. Only single stranded DNA, of which the sequence is not regular enough to form a stable duplex hairpin structure, was selectively absorbed over double-stranded DNA. Among five polynucleotides having different bases such as poly(A), poly(G), poly(C), poly(U) and poly(I), poly(U) and poly(I) were base-specifically adsorbed by PVAd, probably by hydrogen bond formation. The effect of the molecular mass and size of poly(9-vinyladenine) was also examined.

Affinity gel electrophoresis of nucleic acids. Specific base- and shape-selective separation of DNA and RNA on polyacrylamide-nucleobase conjugated gel.

Two types of affinity gels consisting of cross-linked polyacrylamide and affinity ligands possessing nucleic acid bases were prepared. One type of gel was polyacrylamide-poly(vinylnucleobase) conjugated gel, where the poly(vinylnucleobase) such as poly(9-vinyladenine) (PVAd) bearing a nucleobase in the side-chain was entrapped in the gel matrix. The other type of gel, in which a nucleobase such as adenine is chemically bonded to polyacrylamide gel, was prepared by copolymerization of acrylamide, cross-linker and 9-vinyladenine. These affinity gels, especially the former, demonstrated characteristic nucleobase- and shape-selective separation of nucleic acids. The gels showed high affinity for single-stranded DNA and both single- and double-stranded polynucleotides and could separate a double-stranded DNA in mixtures of double-stranded DNA and polynucleotides. The electrophoretic mobilities of poly(uridylic acid) and poly(inosinic acid) were selectively retarded even in the presence of 7 M urea. The electrophoretic behaviours of nucleic acids on the polyacrylamide-PVAd conjugated gels were compared with those on the agarose-PVAd conjugated gel. The effects of urea, temperature and concentration of PVAd were also examined. The polyacrylamide-PVAd conjugated gel served to elucidate interactions between PVAd and nucleic acids that could not be detected by usual spectroscopic methods.

A novel biomaterial: poly(dimethylsiloxane)-polyamide multiblock copolymer I. Synthesis and evaluation of blood compatibility.

Aramid-silicone resins (PASs) consisting of aromatic polyamide (aramid) and poly(dimethyl-siloxane) (PDMS) segments were synthesized by low temperature solution polycondensation. For the evaluation of blood compatibility in vitro, two kinds of experiments were carried out. One was the thromboxane B2(TXB2) release test from platelets attaching to PAS and Biomer. The other was the observation of the platelet adhesion on the surfaces of PAS by scanning electron microscopy (SEM). The results indicated that PAS was bio-inert in vitro. The surface chemical composition of PAS films was investigated by means of electron probe micro analysis (EPMA), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle measurements. The relationship between blood compatibility and surface composition of PAS is discussed.

Specific base recognition of oligodeoxynucleotides by capillary affinity gel electrophoresis using polyacrylamide-poly(9-vinyladenine) conjugated gel.

Poly(9-vinyladenine) was synthesized and utilized as an affinity macroligand entrapped within the gel matrix. Base-specific separation of oligodeoxynucleotides was achieved with high resolution and high speed by electrophoresis, using capillaries filled with conjugated polyacrylamide-poly(9-vinyladenine) gel. Oligothymidylic acids were selectively separated from the mixture of oligothymidylic and oligodeoxyadenylic acids by utilizing a specific hydrogen bonding between poly(9-vinyladenine) and oligothymidylic acids. Migration time and resolution of oligodeoxynucleotides were influenced by several parameters, such as the size of poly(9-vinyladenine), capillary temperature, and concentrations of poly(9-vinyladenine) and urea. Some guidelines are presented, based on the theoretical formulation of the effect of these parameters, in order to find optimum electrophoretic conditions. Analytical capillary affinity gel electrophoresis was developed for the selective and sensitive base recognition of oligodeoxynucleotides with efficiencies as high as several 10(6) plates/m by using a urea-gel capillary with poly(9-vinyladenine) and temperature-programming.

Immobilization of human thrombomodulin on glass beads and its anticoagulant activity.

Human thrombomodulin (TM) was for the first time immobilized on glass beads by the reaction between the carboxyl group of TM and the amino group of glass beads using water-soluble carbodiimide. Immobilized human TM exhibited both anticoagulant activity and inhibition of platelet aggregation of human blood.

Spectroscopic study of the interaction between poly-(9-vinyladenine) and single or multistrand RNA.

The interaction between poly(9-vinyladenine) (PVAd) and poly[r(U)] was investigated by means of uv, CD, 1H-, and 31P-nmr spectroscopies. The interaction was dependent on the molecular weight of PVAd determined by uv and CD spectroscopies. Based on imino proton nmr, it was clearly found that PVAd formed the complex with poly[r(U)] by complementary hydrogen bonding. The interaction of PVAd with double- and triple-stranded helices of RNA was also investigated by uv melting behavior and 31P-nmr spectroscopy. The results suggested that PVAd could not interact with the double-stranded poly[r(A)].poly[r(U)] but did with the triple-stranded RNA.