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Biomedical subjects

Eiichi Nakamura

Publications and source records attributed to Eiichi Nakamura.

At least 73 records · Page 4Linked to original sources
PubMed2003

Regioselective synthesis of [60]fullerene eta 5-indenide R3C60- and eta 5-cyclopentadienide R5C60- bearing different R groups.

Treatment of a 1,7-diorgano[60]fullerene with Grignard reagents or organocopper reagents affords a [60]fullerene indenide or a [60]fullerene cyclopentadienide regioselectively in good to excellent yields. These reactions gave an insight into the reaction mechanism of the organocopper penta-addition reaction of [60]fullerene, giving [60]fullerene cyclopentadienide in quantitative yield.

Journal Article↗
PubMed2003

Enantioselective synthesis of alpha-substituted ketones by asymmetric addition of chiral zinc enamides to 1-alkenes.

A zinc enamide of a chiral imine derived from a ketone and (S)-valinol or (S)-t-leucinol undergoes addition to 1-alkene to generate a gamma-zincioimine intermediate, which reacts with a carbon electrophile to give upon hydrolysis an optically active alpha-substituted ketone in good yield. The stereoselectivity of the addition reaction may reach 99% for the reaction of a cyclohexanone imine with ethylene.

Journal Article↗
PubMed2003

Iron-catalyzed regio- and stereoselective ring opening of [2.2.1]- and [3.2.1]oxabicyclic alkenes with a Grignard reagent.

[reaction: see text] Arylative and alkenylative ring-opening reactions of a [2.2.1]- or [3.2.1]oxabicyclic alkene with a Grignard reagent take place in the presence of a catalytic amount of iron(III) chloride and a stoichiometric amount of TMEDA to produce a highly substituted 3-cyclohexen-1-ol or 3-cyclohepten-1-ol in good yield with high regio- and stereoselectivity.

Journal Article↗
PubMed2003

Synthesis, structure, and aromaticity of a hoop-shaped cyclic benzenoid [10]cyclophenacene.

The first hoop-shaped cyclic benzenoid compounds, [10]cyclophenacene derivatives that contain 40 pi electrons, have been synthesized in three or four steps from [60]fullerene by rationally designed chemical modification. The compounds thus synthesized are chemically stable, yellow-colored, luminescent, and EPR-silent. X-ray crystallographic analysis provided high precision structural data sets. On the basis of these results and theoretical investigations, the new cyclic benzenoid molecules were proven to be aromatic.

Journal Article↗
PubMed2003

Reaction pathways of the Simmons-Smith reaction.

The cyclopropanation reaction of an alkene with a metal carbenoid has been studied by means of the B3LYP hybrid density functional method. The cyclopropanation of ethylene with a lithium carbenoid or a zinc carbenoid [Simmons-Smith (SS) reagent] goes through two competing pathways, methylene transfer and carbometalation. Both processes are fast for the lithium carbenoid, while, for the zinc carbenoid, only the former is fast enough to be experimentally feasible. The reaction of an SS reagent (ClZnCH(2)Cl) with ethylene and an allyl alcohol in the presence of ZnCl(2) was also studied. The allyl alcohol reaction was modeled with an SS reagent/alkoxide complex (ClCH(2)ZnOCH(2)CH=CH(2)) formed from the SS reagent and allyl alcohol. Two modes of acceleration were found. The first involves the well-accepted mechanism of 1,2-chlorine migration, and the second involves a five-centered bond alternation. The latter was found to be more facile than the former and to operate equally well both with ethylene and with aggregates of SS reagent/alkoxide complexes. Calculations on the SS reaction with 2-cyclohexen-1-ol offer a reasonable model for the hydroxy-directed diastereoselective SS reaction, which has been used for a long time in organic synthesis.

Journal Article↗
PubMed2003

Theoretical studies on structures and reactivities of organocuprate(I) and organocopper(III) species.

Systematic evaluation of method and basis set on the structure and energetics of organocuprate(I) and organocopper(III) species has been carried out. Various structures of organocuprate(I) and organocuprate(III) complexes were optimized with the HF, MP2, and B3LYP methods, and compared with the structures determined by X-ray crystallography (i.e., Me(2)Cu(I)(-), (CF(3))(4)Cu(III)(-)). Both the MP2 and B3LYP methods reasonably reproduce the X-ray structures while the HF method does not. Using larger basis set and incorporating the relativistic effects for Cu afford the best results. In the studies on the energetics of a Libond;Cu cluster model (Me(2)CuLi. LiCl) and Me(3)Cu model with the MP2, MP3, MP4DQ, MP4SDQ, CCSD(T), and B3LYP methods, the B3LYP method gives energetics similar to those obtained with the CCSD(T) method with much less cost, and hence, is judged to be the best practical method. The studies have shown that B3LYP method with the basis set incorporating the relativistic effective core potentials for Cu and the 6-31G* basis set for the rest is the theoretical method that is the most cost-effective for the studies of the structure and energetics of organocuprate(I) and organocopper(III) species.

Journal Article↗
PubMed2003

Functionalized fullerenes in water. The first 10 years of their chemistry, biology, and nanoscience.

Fullerenes are entirely insoluble in water, but suitable functionalization makes the molecules soluble. Studies on water-soluble fullerene derivatives led to the discovery of the interaction of organofullerenes with DNA, proteins, and living cells, which was first reported in the summer of 1993. Subsequent studies have revealed interesting biological activity aspects of organofullerenes owing to their photochemistry, radical quenching, and hydrophobicity to form one- to three-dimensional supramolecular complexes. In these areas of research, synthetic organic chemistry has played an important role in the creation of tailor-made molecules.

Animals↗
PubMed2003

Effect of distraction frequency on bone formation during bone lengthening: a study in chickens.

We compared the effects of two distraction frequencies on bone formation during tibial lengthening by evaluating radiographs, bone mineral density, and histological findings. In 15 mature White Leghorn chickens, both tibiae were distracted at a rate of 0.75 mm/day for 10 days. The distraction frequency was 2 steps (0.375 mm/12 hour) by hand on the right side and 120 steps (0.00625 mm/12 min) by autodistractor on the left. Serial radiographs showed faster bone formation on the 120-step side than on the 2-step side. Bone mineral density on the 120-step side was also higher than that on the 2-step side at all times. On the 2-step side, endochondral ossification was marked in the early stage of distraction; then intramembranous ossification became the main mechanism of bone formation. On the 120-step side, however, intramembranous bone formation predominated throughout the study. Our findings support the contention that, at least in skeletally mature chickens, an increase in the distraction frequency improves osteogenesis during bone lengthening.

Animals↗
PubMed2002

Stacking of conical molecules with a fullerene apex into polar columns in crystals and liquid crystals.

Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C(60) fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.

Journal Article↗
PubMed2002

Hybrid of ferrocene and fullerene.

"Bucky ferrocenes", molecular hybrids of ferrocene and fullerene, have been synthesized in good yield on gram scale by treatment of C(60)HMe(5) or C(70)HMe(3) with [FeCp(CO)(2)](2) and their structures studied with physical methods including X-ray crystallography.

Journal Article↗
PubMed2002

Mechanism of C[bond]H bond activation/C[bond]C bond formation reaction between diazo compound and alkane catalyzed by dirhodium tetracarboxylate.

The B3LYP density functional studies on the dirhodium tetracarboxylate-catalyzed C-H bond activation/C-C bond formation reaction of a diazo compound with an alkane revealed the energetics and the geometry of important intermediates and transition states in the catalytic cycle. The reaction is initiated by complexation between the rhodium catalyst and the diazo compound. Driven by the back-donation from the Rh 4d(xz) orbital to the C[bond]N sigma*-orbital, nitrogen extrusion takes place to afford a rhodium[bond]carbene complex. The carbene carbon of the complex is strongly electrophilic because of its vacant 2p orbital. The C[bond]H activation/C[bond]C formation proceeds in a single step through a three-centered hydride transfer-like transition state with a small activation energy. Only one of the two rhodium atoms works as a carbene binding site throughout the reaction, and the other rhodium atom assists the C[bond]H insertion reaction. The second Rh atom acts as a mobile ligand for the first one to enhance the electrophilicity of the carbene moiety and to facilitate the cleavage of the rhodium[bond]carbon bond. The calculations reproduce experimental data including the activation enthalpy of the nitrogen extrusion, the kinetic isotope effect of the C[bond]H insertion, and the reactivity order of the C[bond]H bond.

Journal Article↗
PubMed2002

Synthesis of disubstituted cucurbit[6]uril and its rotaxane derivative.

Synthesis of diphenyl cucurbit[6]uril (CB[6]) has been achieved via co-oligomerization of diphenyl glycoluril and unsubstituted glycoluril. The unsymmetrically substituted CB[6], Ph(2)CB[6], was further converted to a rotaxane incorporating bis(dinitrophenyl)spermine. [reaction: see text]

Bridged-Ring Compounds↗
PubMed2002

Intraoperative lymphatic mapping and sentinel lymph node sampling in esophageal and gastric cancer.

Recent studies for SN mapping of esophageal and gastric carcinoma show that the SN concept is valid even for upper GI cancers with multidirectional and complicated lymphatic flow. The relatively high incidence of anatomic skip metastasis can be attributed to aberrant distribution of SNs. An individualized and minimally invasive surgical approach can be applicable to management of esophageal and gastric carcinoma based on SN status. Although there are several issues to be resolved, this novel procedure has the potential for great benefit to improve quality control in the treatment of upper GI cancer. Well-designed clinical trials of lymphatic mapping for upper GI cancer will be essential to determine whether this technique is widely applicable in the management of these tumors.

Esophageal Neoplasms↗
PubMed2002

Thermal reactions of dipolar trimethylenemethane species.

Installation of two alkoxy groups on a terminal methylene of trimethylenemethane (TMM) dramatically alters the electronic state and the reactivities of the TMM. Thermolysis of a 1,1-dialkoxy-2-methylenecyclopropane generates such a TMM, which exhibits a marked singlet dipolar character. It undergoes [3 + 2] cycloadditions to a variety of electron-deficient unsaturated compounds including alkenes, alkynes, oximes, carbonyl compounds, and fullerenes and reacts with active methelene compounds and organozinc reagents as a 1,3-dipolar synthon.

Journal Article↗