Synthesis of Enkephalin analogs via asymmetric hydrogenation of dehydropeptide building blocks

[Ac-D-Tyr¹, D-Ala², Leu⁵-OMe]Enkephalin and [Ac-Tyr¹, D-Ala², Leu⁵-OMe]Enkephalin were successfully synthesized by the coupling of dipeptide units and tripeptide units which were readily obtained by the asymmetric hydrogenation of the corresponding dehydropeptide building blocks.     

Technetium-99m complexes with steroid-2-aminooxyethyliminodiacetic acid conjugates

Conjugates of 2-aminooxyethyliminodiacetic acid with estrone, testosterone, epiandrosterone, 17-alpha-hydroxy-progesterone and progesterone were synthesized and their complexes with Tc-99m were successfully prepared in good yields, which indicated the agent to be promising for metal-labeling of biomolecules and related substances containing one or more carbonyl groups. The biodistribution and scintigraphic studies in mice bearing Ehrlich tumor and mammary tumor showed that the radioactivity accumulated considerably in the tumor tissues, but the tumor images were somewhat obscured.     

Organocatalytic direct asymmetric aldol reactions in water

We have developed direct asymmetric cross-aldol reactions that can be performed in water without addition of organic solvents. A bifunctional catalyst with a long hydrophobic alkyl chain efficiently catalyzed the reactions and afforded the desired aldol products in excellent yield with high enantiomeric excess, even when only an equal molar ratio of the donor and acceptor was used. These results reveal an effective design strategy for the development of aqueous organocatalytic systems.     

Synthesis of chiral tripeptides by asymmetric hydrogenation of dehydrotripeptides. Remarkable effects of N-protecting groups on stereoselectivity and reactivity

Dehydrotripeptides, X-$\text{C}\text{*}$CH(Rⁱ)-ΔPhe-$\text{C}\text{*}$CH(R^k)COOMe ($\text{3}$: X = ^tBOC-NH,CBZ-NH, CF₃CONH and N₃), were employed for the asymmetric hydrogenation catalyzed by chiral rhodium complexes and it was found that ^tBOC-$\text{3}$ brought about by far the best results. Stereoselective dideuteration of a ^tBOC-$\text{3}$ was successfully performed.     

Acetone hydration in supercritical water: (13)C-NMR spectroscopy and Monte Carlo simulation

The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions. The average number N(HB) of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated from the delta and its temperature dependence, respectively. At 400 degrees C, N(HB) is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative DeltaE at lower water densities (-3.3 kcal/mol at 0.10 g/cm(3) and -0.3 kcal/mol at 0.60 g/cm(3)), in contrast to the positive DeltaE in ambient water (+0.078 kcal/mol at 4 degrees C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of N(HB) calculated at 400 degrees C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters.     

Cyclopolycondensations. VI. Fully aromatic polybenzoxazinones from aromatic poly(amic acids)

New high temperature aromatic polybenzoxazinones of high molecular weight have been prepared by the cyclopolycondensation of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic dicarboxylic acid halides (II). The low temperature solution polymerization techniques afforded poly(amic acid) (III) of high molecular weight in the first step. An open-chain precursor subsequently underwent thermal cyclodehydration along the polymer chain at 200–350°C. in the second step, to give in quantitative yield a fully aromatic polybenzoxazinone (IV) of outstanding heat stability both in nitrogen and in air. The poly(amic acid) is soluble in N-methyl-2-pyrrolidone, and tough, transparent films can be cast from solution. Insoluble aromatic polybenzoxazinone films which possess excellent oxidative and thermal stability were obtained by the heat treatment of the polyamic acid. A detailed account of polymerization conditions in the low temperature solution polymerization of polybenzoxazinones is given, and the reaction mechanisms of cyclopolycondensation of poly(amic acids) and the formation of polybenzoxazinones are discussed.     

Novel five‐membered ring formation by oxidative photocyclization of 4‐(2‐arylvinyl)benzo[a]quinolizinium salts

Oxidative photocyclization of 4‐(2‐arylvinyl)benzo[a]quinolizinium salts ( 6 ) gave five‐ or six‐mem‐bered rings depending on the aryl substituent. The olefins 6a and 6b with a phenyl or naphthyl substituent resulted in a normal six‐membered ring formation to afford 6a‐azoniapicene and 6a‐azoniabenzo[b]picene salts ( 7 and 8 ), respectively. In contrast, the photo‐reaction of pyridyl substituted derivative 6c resulted in novel five‐membered ring formation to yield 3b‐azonia‐5‐(2‐pyridyl)acephenanthrylene salt ( 10 ).     

Direct observation of unstable intermediate species in the reaction of trans-2-butene on ferrierite zeolite by picosecond infrared laser spectroscopy

The reaction dynamics of trans-2-butene adsorbed to acidic hydroxyl groups on the surface of ferrierite zeolite is examined by time-resolved spectroscopy using a tunable infrared picosecond pulse laser system. The transient absorption spectra measured by a two-color pump-probe technique at 188-243 K reveal bleaching and hot bands of the OD stretching mode 2 ps after excitation. This vibrationally excited state relaxes within 20 ps at 188 K, while the bleaching band includes a long-lifetime component that lasts for more than 100 ps at 243 K. Thus, the OD (isotope-exchanged hydroxy groups) stretching band does not entirely recover in this period and is mirrored by an analogous weakening of the CH bending band of the adsorbed trans-2-butene. Simultaneously, three new bands in CH stretching region were observed at 3045, 3095, and 3130 cm(-1). This result suggests the presence of a short-lived intermediate formed by reaction between the acidic hydroxyl groups and adsorbed trans-2-butene.     

Measurement and correlation of liquid–liquid equilibria for acetonitrile + n-alkane systems

The reduction of sulfur content in gasoline and diesel fuel is a great environmental concern to reduce the motor vehicle emissions. Oxidative desulfurization using acetonitrile biphasic system has received much attention in recent years. The oxidative desulfurization can be oxidized the unreactive sulfur contents in the hydrodesulfurization and removed effectively. For the oxidative desulfurization process design and development, liquid–liquid equilibria (LLE) for acetonitrile biphasic systems are needed as fundamental information. In our previous work, LLE for acetonitrile + n-octane and + n-decane systems have been reported. In this work, therefore, LLE for acetonitrile + n-hexadecane system was measured. Furthermore, NRTL equation was applied to correlate the LLE for these three acetonitrile + n-alkane systems.