First enantioselective synthesis of exiguamide,a nitrogen-containing spirocyclic sesquiterpene isolated from the marine sponge Geodia exigua

(+)-Exiguamide is a nitrogen-containing spirocyclic sesquiterpene isolated from the marine sponge Geodia exigua. This study aims to report the first synthesis of both enantiomers of exiguamide, featuring the stereoselective intramolecular cyclopropanation and stereoselective homoconjugate addition of azide to cyclopropyl ketone as the key steps.     

A study on the transition state in the photooxygenations by aromatic amine N-oxides

Oxygen—atom transfer process in the photolysis of aromatic amine N-oxides was suggested to involve the primary oxygen—atom elimination from N-oxides to give “oxene” follwed by its reactions with the oxygen-acceptors.     

Preparation and synthetic application of a novel ketene silyl acetal of methyl trifluoropyruvate

[reaction: see text] A novel trifluoromethyl ketene silyl acetal (4) of methyl trifluoropyruvate (1) was prepared in 82% yield by metal Mg reduction in a (TMS)Cl/THF system. Subsequent carbon-carbon bond formation such as Mukaiyama aldol, Michael addition, and other nucleophilic reactions of 4 at the trifluoromethylated carbon with various electrophiles gave various coupling products in high yields.     

Cellular uptake and photocytotoxicity of glycoconjugated porphyrins in HeLa cells

Thirty-two glycoconjugated porphyrins were synthesized by a modification of Lindsey method in the presence of Zn(OAc)(2).2H(2)O as a template. The Zn(2+) ion template strategy improved the yield about three-fold in the case of meta-substituted tetraphenylporphyrins. In addition, free-base porphyrins were obtained almost quantitatively by demetalation with 4 M HCl. Sixteen deacetylated glycoconjugated porphyrins were tested as candidate photodynamic therapy (PDT) drugs using HeLa cells. Most of the deacetylated glycoconjugated porphyrins showed higher cellular uptake than tetraphenylporphyrin tetrasulfonic acid (TPPS), and 5,10,15,20-tetrakis[4-(beta-D-arabinopyranosyloxy)phenyl]porphyrin (p-5d) in particular showed 18.5-fold higher uptake than TPPS. The photocytotoxicity of 5,10,15,20-tetrakis[4-(beta-D-glucopyranosyloxy)phenyl]porphyrin (p-5a), p-5d and TPPS was examined with HeLa cells, using a light dose of 16 J/cm(2). These photosensitizers had no cytotoxicity in the dark, but their photocytotoxicity increased in the order of TPPS < p-5a < p-5d. These results suggest p-5d is a good candidate for a PDT drug.     

Control of oxygen atom chirality and chelate ring conformation by protected/free sugar hydroxyl groups in glucose-pendant dipicolylamine-copper(II) complexes

A pair of copper(II) complexes 1 and 2 exhibit an enantiomeric chiral center at the oxygen atom that coordinates to the metal center. The configurations of the oxygen atom chirality and the chelate ring conformation are simply controlled by protected/free hydroxyl groups of the sugar moiety, yielding mirror image CD spectra. In this system, repulsive and attractive forces are used to regulate chirality on the copper-coordinated oxygen atom both in the solid state and in solution.     

Deuterium diffusion in vanadium deuterides (VDx; 0.4?x?0.6) studied by H NMR

Sites and dynamics of deuterium in VD_0.50 as well as in VD_0.40 and VD_0.57 have been studied by means of X-ray diffraction, differential scanning calorimetry and ²H NMR. VD_0.40 consists of the body-centered-cubic (bcc) α_D and body-centered-tetragonal (bct) β_D phases at room temperature and only the octahedral (O) sites are occupied in the β_D phase. On the other hand, in VD_0.50, consisting of the bctβ_D phase at room temperature, the O site is dominantly occupied with a small occupancy of the tetrahedral (T) sites in the β_D phase. VD_0.57 is composed of the bccα′_D (a high-deuterium-concentration phase of the α_D phase) and bctβ_D phases at room temperature, and the occupancy of the T sites is observed. The mean activation energy (E_D) of the deuterium diffusion is much larger for the O sites than for the T sites, and the diffusion is also much slower in the O sites. The mean E_D values for the O sites are almost the same in the β_D phase of VD_0.40 and VD_0.50, although the distribution of the mean residence time is much larger in VD_0.50 than in VD_0.40.     

Structure of Ti1−yVyHx alloys studied by X-ray diffraction and by 1H and 51V NMR

The structure of the TiVH system is studied by X-ray diffraction and ¹H and ⁵¹V NMR measurements. It is shown that the solid solution of TiV is separated into a few phases by hydrogenation. They are α-TiVH, β-TiVH, γ-TiVH, and γ-TiH phases, which are assumed to have their origins either in TiH_x or in VH_x. The concentration of each phase can be estimated by NMR, which is dependent on the composition of the system. The phase separation caused by hydrogenation is due to the large stability of the γ-TiH phase.     

A glucosamine-dipicolylamine conjugate of 99mTc(I) and 186Re(I) for use in imaging and therapy

The synthesis and metal complexation of a glucosamine-appended 2,2'-dipicolylamine ligand to the tricarbonyls of 99mTc and 186Re is described; the ligand was found to bind in a tridentate fashion with the glucosamine function remaining pendant, and the 99mTc complex was found to exhibit exceptional stability towards in vitro ligand exchange experiments.     

Model Studies of TTQ-Containing Amine Dehydrogenases

The reactions of a TTQ model compound [1, 3-methyl-4-(3'-methylindol-2'-yl)indole-6,7-dione] with several amines have been investigated in organic media to obtain mechanistic information on the action of quinoprotein methylamine and aromatic amine dehydrogenases. It has been found that compound 1 acts as an efficient catalyst for the autorecycling oxidation of benzylamine by molecular oxygen in CH(3)OH. In order to evaluate the oxidation mechanism of amines by 1, the product analyses and kinetic studies have been carried out under anaerobic conditions. In the first stage of the reaction of 1 with amines, 1 is converted into an iminoquinone-type adduct (so-called substrateimine), which was isolated and characterized by using cyclopropylamine as a substrate. The observed NOE of the isolated product indicates clearly that the addition position of the amine is C-6 of the quinone. The molecular orbital calculations suggest that the thermodynamic stability of the carbinolamine intermediate is a major factor to determine such regioselectivity; the C-6 carbinolamine is more stable than the C-7 counterpart by 2.9 kcal/mol. The reactivity of several primary amines and the electronic effect of the p-substituents of benzylamine derivatives in the iminoquinone formation suggest that the addition step of the amine to the quinone is rate-determining. When amines having an acidic alpha-proton such as benzylamine derivatives are employed as substrates, formation of the iminoquinone adduct was followed by rearrangement to the productimine. The kinetic analysis has revealed that this rearrangement consists of noncatalyzed and general base-catalyzed processes. Large kinetic isotope effects of 7.8 and 9.2 were observed for both the noncatalyzed and general base-catalyzed processes, respectively, since these steps involve a proton abstraction from the alpha-position of the substrate. In the reaction with benzhydrylamine, the product imine was isolated quantitatively and well characterized by several spectroscopic data. In the case of benzylamine, the product imine is further converted into the aminophenol derivative by the imine exchange reaction with excess benzylamine. These results indicate clearly that the amine oxidation by compound 1 proceeds via a transamination mechanism as suggested for the enzymatic oxidation of amines by TTQ cofactor.