A simple and simultaneous determination of acyclovir and ganciclovir in human plasma by high-performance liquid chromatography

A simple high-performance liquid chromatographic method was developed for the simultaneous determination of the therapeutic levels of acyclovir and ganciclovir in human plasma. After precipitation of plasma proteins with 6% perchloric acid, acyclovir and ganciclovir were simultaneously determined by reversed-phase chromatography with spectophotometric detection at 254 nm. The peak heights for acyclovir and ganciclovir were linearly related to their concentrations ranging from 0.063 to 2.080 micro g/mL. The recovery was 100.48-102.84% for acyclovir and 99.26-103.07% for ganciclovir. The intra- and inter-day relative standard deviation values were in the range 0.186-8.703% for acyclovir and 0.137-6.424% for ganciclovir. The detection limits for both compounds were 0.01 micro g/mL determined as the signal-to-noise ratio of 3. The present method is applicable to therapeutic monitoring during antiviral medication.     

Effect of adsorbed water on the electrorheology of silica suspensions

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η^*|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water.     

Synthesis and absolute structure of manzacidin B

[reaction: see text] Four possible stereoisomers of manzacidin B were synthesized using stereochemically defined synthetic routes via the azide 7 and oxazoline 11 starting with the (R)-alpha-methyl Garner aldehyde 5. Comparisons of the spectroscopic data of the synthetic isomers 4a-d with those of the natural manzacidin B revised the proposed structure 3 to (4S,5S,6R)-4d.     

Michael addition reactions between chiral equivalents of a nucleophilic glycine and (S)- or (R)-3-[(E)-enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a general method for efficient preparation of beta-substituted pyroglutamic acids. Case of topographically controlled stereoselectivity

This paper describes a systematic study of addition reactions between the chiral Ni(II) complex of the Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone and (S)- or (R)-3-[(E)-enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a general and synthetically efficient approach to beta-substituted pyroglutamic acids and relevant compounds. These reactions were shown to occur at room temperature in the presence of nonchelating organic bases and, most notably, with very high (>98% diastereomeric excess (de)) stereoselectivity at both newly formed stereogenic centers. The stereochemical outcome of the reactions was found to be overwhelmingly controlled by the stereochemical preferences of the Michael acceptors, and the chirality of the glycine complex influenced only the reaction rate. Thus, in the reactions of both the (S)-configured Ni(II) complex and the Michael acceptors, the reaction rates were exceptionally high, allowing preparation of the corresponding products with virtually quantitative (>98%) chemical and stereochemical yields. In contrast, reactions of the (S)-configured Ni(II) complex and (R)-configured Michael acceptors proceeded at noticeably lower rates, but the addition products were obtained in high diastereo- and enantiomeric purity. To rationalize the remarkably high and robust stereoselectivity observed in these reactions, we consider an enzyme-substrate-like mode of interaction involving a topographical match or mismatch of two geometric figures. Excellent chemical and stereochemical yields, combined with the simplicity and operational convenience of the experimental procedures, render the present method of immediate use for preparing various beta-substituted pyroglutamic acids and related compounds.     

Enantioselectively catalyzed oxidation of 3,4-dihydroxy-l-phenylalanine by N-lauroyl L or D-histidine-Cu(II) complex in CTABr micelles.

In order to investigate the enzyme model reaction the oxidation of 3,4-dihydihydroxy-L-phenylalanine(L-DOPA) was carried out using optically active catalyst, N-lauroyl L or D-histidine-Cu(II) complex(L or D-LauHis-Cu(II)), showing appreciable enantioselectivity in the presence of the mixed micelles with CTABr.     

Fluorescence up-conversion study of excitation energy transport dynamics in oligothiophene-fullerene linked dyads

Photoinduced excitation energy transport dynamics in oligothiophene-fullerene linked dyads, nT-C60 (n = 4, 8, and 12), have been investigated by femtosecond fluorescence up-conversion. In 8T-C60 and 12T-C60, each time profile of the fluorescence due to the 1nT* moiety consists of two components. The sub-picosecond component and a few picosecond components were experimentally evaluated depending on the lengths of oligothiophenes (n =8 and 12) and on the analyzing wavelength of the fluorescence. However, the time trace of the fluorescence due to 14T*-C60 decayed with a single short component in approximately 300 fs due to direct excited energy transfer (EET) from the 14T* moiety to the C60 moiety. On the basis of the kinetic models considering the short and long locally pi-conjugative thiophene segments in 8T-C60 and 12T-C60, the rate parameters of the elemental processes were evaluated. Sub-picosecond time constants of nT-C60 were found to be EET from the thiophene segment vicinal to the C60 moiety and intrachain energy transfer. Slower picosecond dynamics mainly corresponds to EET from the thiophene segments apart from the C60 moiety.     

Synthesis and antiulcer activity of optical isomers of 2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl]propionic acid (rebamipide).

The enantiomers of 2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl] propionic acid [(+/-)-1, rebamipide, OPC-12759], a new antiulcer agent that enhances mucosal resistance, were synthesized from optically active alpha-amino acid derivatives of 2(1H)-quinolinone. The key intermediates, alpha-amino acid derivatives, were prepared by asymmetric synthesis and optical resolution. The (+)-1 was about 1.7 times as potent as the (-)-isomer in antiulcer activity against ethanol-induced gastric ulcers.     

Aminyl radical cyclization by means of anodic oxidation. Stereoselective synthesis of cis-1-methyl-2,5-disubstituted pyrrolidines

Neutral aminyl radicals generated by anodic oxidation of lithium alkenylamides 2 undergo a stereoselective cyclization to give $\text{cis}$-1-methyl-2,5-disubstituted pyrrolidines 4. Their $\text{cis}$ stereochemistry was confirmed by a comparison with $\text{trans}$-1,2-dimethyl-5-phenylpyrrolidine, the structure of which was established by X-ray crystallographic analysis of its quarternary ammonium bromide 6.     

The efficient direct synthesis of N,O-acetal compounds as key intermediates of discorhabdin A: oxidative fragmentation reaction of alpha-amino acids or beta-amino alcohols by using hypervalent iodine(III) reagents

Hypervalent iodine(III) reagents are readily available, easy to handle, and have a low toxicity and similar reactivities to those of heavy metal reagents, and hence they are used for various oxidative reactions. The oxidative cleavage of alkynes or carbonyl compounds by using bis(trifluoroacetoxy)iodo(III) pentafluorobenzene (C(6)F(5)I(OCOCF(3))(2)) has been reported. Herein, the efficient direct synthesis of N,O-acetal compounds as key intermediates of discorhabdin A, by the oxidative fragmentation reaction of alpha-amino acids or beta-amino alcohols by using C(6)F(5)I(OCOCF(3))(2), is described.     

Hybrid Mesoporous-Silica Materials Functionalized by Pt(II) Complexes: Correlation between the Spatial Distribution of the Active Center, Photoluminescence Emission, and Photocatalytic Activity

[Pt(tpy)Cl]Cl (tpy: terpyridine) was successfully anchored to a series of mesoporous-silica materials that were modified with (3-aminopropyl)triethoxysilane with the aim of developing new inorganic-organic hybrid photocatalysts. Herein, the relationship between the luminescence characteristics and photocatalytic activities of these materials is examined as a function of Pt loading to define the spatial distribution of the Pt complex in the mesoporous channel. At low Pt loading, the Pt complex is located as an isolated species and exhibits strong photoluminescence emission at room temperature owing to metal-to-ligand charge-transfer ((3) MLCT) transitions (at about 530?nm). Energy- and/or electron-transfer from (3) MLCT to O(2) generate potentially active oxygen species, which are capable of promoting the selective photooxidation of styrene derivatives. On the other hand, short Pt???Pt interactions are prominent at high loading and the metal-metal-to-ligand charge-transfer ((3) MMLCT) transition is at about 620?nm. Such Pt complexes, which are situated close to each other, efficiently catalyze H(2) -evolution reactions in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light irradiation. This study also investigates the effect of nanoconfinement on anchored guest complexes by considering the differences between the pore dimensions and structures of mesoporous-silica materials.