Synthesis of the highly potent prostanoid FP receptor agonist, AFP-168: a novel 15-deoxy-15,15-difluoroprostaglandin F2α derivative

A novel 15-deoxy-15,15-difluoro-prostaglandin(PG)F_2α derivative 6 (AFP-168) has been synthesized from the Corey aldehyde in six steps. A key aspect of this route is difluorination of an enone and a stereoselective Wittig reaction. The compound shows high affinity to the FP receptor and potent activities for an anti-glaucoma agent.     

Total synthesis and absolute configuration of otteliones A and B, novel and potent antitumor agents from a freshwater plant

[reaction: see text] The first enantioselective total synthesis of otteliones A and B, biologically important and structurally novel natural products, has been successfully achieved. This total synthesis fully confirms the absolute configuration of these natural products.     

Efficient deprotection of N-benzyloxycarbonyl group from amino acids by hydroxyapatite-bound Pd catalyst in the presence of molecular hydrogen

Hydroxyapatite-bound Pd catalyst was found to be highly effective for the deprotection of N-benzyloxycarbonyl group from amino acids in the presence of molecular hydrogen. The catalyst was also applicable to the hydrogenolysis of a sterically encumbered core-Z-protected poly(amido amine) dendrimer, affording the dendritic amino compound in 99% yield.     

Coherent tunneling of proton in the intramolecular hydrogen bond of crystalline bromo-hydroxyphenalenone at low temperature

Infrared absorption spectra of 5-bromo-9-hydroxyphenalenone were measured and analyzed in detail as a function of temperature. An intense and broad peak at 83 cm⁻¹ occurring in the protonated crystal, but not in the deuterated analog, arises from the coherent tunneling motion of the hydrogen in the intramolecular hydrogen bond. Strong temperature dependence of the frequency and width of the tunneling peak determined by fitting the Gaussian or Lorentzian peak shape function is reproduced well by three-parameter functions representing the thermal population of the excited state of the tunneling proton.     

Improvement of impact toughness of sugar-coated tablets manufactured by the dusting method

The purpose of this study was to improve the impact toughness of sugar-coated tablets manufactured by a dusting method. The effects of sugar-coating formulations, which were the sugar-coating suspension formulations and the dusting powder formulations, on impact toughness of sugar-coated tablets were investigated. Impact toughness of sugar-coated tablets was measured by the friability test. We found that the dusting powder formulation was a control factor in impact toughness of sugar-coated tablets manufactured by the dusting method. The dusting method using dusting powder containing 20% microcrystalline cellulose (MCC, Avicel PH-F20) was a useful method for improvement of the impact toughness of sugar-coated tablets. The mechanism of improvement of impact toughness was that MCC in the subcoating layer resulted in a tight bond between the subcoating layer and the smoothing layer and prevented separation of the two layers on impact, because MCC improved the wettability of the subcoating layer, increased the surface roughness of the subcoating layer, and played the role of a binder between the two layers. We confirmed that the MCC between the subcoating layer and the smoothing layer acts to prevent separation of the two layers by impact. We demonstrated that MCC is a suitable material for sugar-coating in order to improve the impact toughness of sugar-coated tablets.     

Aggregation of Chlorophyll a' in Aqueous Methanol

An aggregate of chlorophyll a' (Chi a' , C13²-epimer of ChI a ) formed in a methanovwater (40160, vol/vol) mixed solvent was examined by visible absorption, circular dichro-ism (CD), fluorescence and resonance Raman spectrosco-pies in relation to its possible involvement in the core of photosystem I reaction center. The Chl a' aggregate exhibited a sharp, double-peaked absorption spectrum (690 and 715 nm) accompanied by an intense, conservative CD signal. The fluorescence excitation polarization spectrum showed that the doublet results from the exciton splitting in a single aggregate species. Time-dependent changes in the spectroscopic properties clearly point to a simple transformation process from one molecular species to another, though a minor component appears to coexist. This conclusion was supported also by the principal multicom-ponent spectral estimation analysis of the transients of absorption spectra. The species formed at the initial stage is most probably a T-shaped dimer or oligomer, which is then gradually converted into the final major product, presumably a stacked dimer. In both of these states, the Chl molecules are linked together via direct coordination of the C13'keto carbonyl oxygen onto the Mg atom of neighboring molecules, as suggested by almost identical resonance Raman spectra in ordinary and deuterated methanovwater mixed solvents. The stacked dimers probably further associate to form a colloidal state in this solvent system. Based on these results, a model for the Chl a' aggregation is proposed.     

Determination of chemical structures by 1H- and 13C-NMR for thermally degraded linear high density polyethylene

Chemical structures were determined for polymer residues obtained by thermal degradation of a linear high-density polyethylene. Terminal methyl, double bonds (terminal vinyl, trans-vinylene, and vinylidene), and long chain branching were identified by using ¹H- and ¹³C-NMR spectra data. The number of these functional groups per 1000 C was quantified with a relative error of about 10%.     

A new approach for the investigation of isoprenoid biosynthesis featuring pathway switching,deuterium hyperlabeling,and 1H NMR spectroscopy. The reaction mechanism of a novel streptomyces diterpene cyclase

Recent methodology for the investigation of isoprenoid biosynthesis featuring pathway switching and hyperdeuteration has shown significant advantages in elucidating the reaction mechanism of a novel Streptomyces diterpene cyclase with use of precise atom-level analysis. Insight into the cyclization mechanism involved in the conversion of geranylgeranyl diphosphate (GGPP) into a clerodane hydrocarbon terpentetriene was obtained by heterologous expression in doubly engineered Streptomyces lividans of a diterpene cyclase gene derived from Streptomyces griseolosporeus, a producer of an unique diterpenoid cytotoxic antibiotic terpentecin, and by in vivo labeling with mevalonate-d(9). The cyclization involved electrophilic protonation, cationic ring closure, Wagner-Meerwein-type rearrangements, and deprotonation. A key feature was that the labeled metabolite as a mixture of predominantly deuterated mosaic molecules provided sufficient information that close analysis of the labeling pattern for each individual isoprene unit was achieved primarily by (1)H NMR spectroscopy. The cyclization of GGPP into the clerodane skeleton catalyzed by the cyclase appears to involve Si-face specific protonation, intermediates with A/B chair-boat conformation, and specific methyl and hydride migrations to give an intermediary C-4 carbocation. Subsequent collapse of the cation through specific removal of the initiating proton and final elimination of diphosphate gives rise to the terpentetriene hydrocarbon.     

EPR STUDIES OF TRAPPED SINGLET OXYGEN (lO2) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

Hypocrellin A, a peryloquinone derivative, has recently been isolated from the sacs of the fungus Hypocrella bambusae. This pigment, in combination with phototherapy, has been used in human medicine to cure various skin diseases. The generation of singlet oxygen during photoirradiation of Hypocrellin A (HA) was detected as an oxidation product of a sterically hindered amine (tetramethylpiperidine oxide; TEMPO) by electron paramagnetic resonance (EPR) spectroscopic techniques. Azide inhibited the EPR signal intensity in a dose-dependent manner with a quenching rate constant of 3.86 x 10(8) M-1s-1 in ethanol. Deuterated solvents, known to increase the lifetime of singlet oxygen, augmented the EPR signal intensity. The rate of production of singlet oxygen was dependent not only upon the concentration of HA and the time of irradiation but also on the oxygen content of the reaction mixture. The hyperfine splitting constant (aN = 16.3 G) and g-value (g = 2.0056) of the photoproduct of TEMP-singlet oxygen and TEMPO were found to be identical. This indicates that the nitroxide species detected by EPR spectroscopy generated by reacting TEMP with photogenerated 1O2 is TEMPO. The rate constant (kT) for the reaction of singlet oxygen with TEMP to form TEMPO radical was found to be 5.3 x 10(5) M-1s-1.     

Ion-specific swelling behavior of poly(ethylene oxide) gel and the correlation to the intrinsic viscosity of the polymer in salt solutions

The swelling behavior of a poly(ethylene oxide) (PEO) gel in solutions of various salts was investigated for the 0-2 mol dm^-3 region. The gel deswelled in solutions of sodium salts, but the ion specificity for anions was not clearly observed. The gel swelled in solutions containing strongly hydrated cations and the degree of swelling of the gel at 2 mol dm^-3 was in the following orders: CsClhKCl2222. These results were interpreted in terms of interactions between the polymer and the ions through the hydration layers of the cations. The dimensions of PEO estimated from the results of the intrinsic viscosity of PEO in salt solutions were in accordance with this interpretation. Comparison of the swelling behavior of the PEO gel and that of a poly(vinyl alcohol) gel revealed the large difference in the effect of anions.