Ken'ichi Takeuchi

Use of naphthalene as a solvent for selective formation of the 1:1 diels-alder adduct of C60 with anthracene

Abstract A reaction of C 60 with an equimolar amount of anthracene in refluxing naphtlhalene gives the 1:1 Diels-Alder adduct in 67% yield based on consumed C 60 : the adduct was fully characterized by IR, UV-vis, 1 H and 13 C NMR, and MS spectroscopy, and exhibited reversible reduction waves at the potential 0.11 to 0.19 V more negative and an irreversible oxidation peak at the potential 0.11 V less positive than those of C 60 itself.

Changes in temperature preferences and energy homeostasis in dystroglycan mutants.

Temperature affects the physiology, behavior, and evolution of organisms. We conducted mutagenesis and screens for mutants with altered temperature preference in Drosophila melanogaster and identified a cryophilic (cold-seeking) mutant, named atsugari (atu). Reduced expression of the Drosophila ortholog of dystroglycan (DmDG) induced tolerance to cold as well as preference for the low temperature. A sustained increase in mitochondrial oxidative metabolism caused by the reduced expression of DmDG accounted for the cryophilic phenotype of the atu mutant. Although most ectothermic animals do not use metabolically produced heat to regulate body temperature, our results indicate that their thermoregulatory behavior is closely linked to rates of mitochondrial oxidative metabolism and that a mutation in a single gene can induce a sustained change in energy homeostasis and the thermal responses.

Linear free-energy relationships between stability parameters of substituted tropylium and cyclopropenylium ions as measured by reduction rate with chromium(II), reduction potential, charge-transfer energy, and pKR+ values

Abstract Nine tropylium ions have been synthesized and the empirical stability parameters (i)–(iv) have been measured along with the parameters of known tropylium and cyclopropenylium ions: (I) the Cr(II)-ion reduction rate constant ( k 2 ) in 10% aqueous hydrochloric acid at 25.0°; (ii) the charge-transfer frequency ( v CT max ) with pyrene in 1,2-dichloroethane; (iii) the reduction peak potential (E red ) in dichloromethane or in acetonitrile; and (iv) the pK R + values in 23% aqueous ethanol, in 50% aqueous ethanol, and in 50% aqueous acetonitrile. When the linear free-energy relationships (LFER) of these and previously reported results were examined (a) between the charge-transfer energy {(E CT)}, 119.5 × v CT max (cm −1 ), kJ mol −1 and the E red {(96.36 × E red (V), kj mol −1 )}; (b) between the log k 2 {(5.70 × log k 2 (1 mol −1 s −1 ), kJ mol −1 )} and the E red ; and (c) between the log k 2 and the E CT , satisfactory interrelations were found. On the basis of these LFERs the electron affinity scales (log k 2 , E CT , and E red ) are interchangeable for each other as the stability parameters for the cyclopropenylium and tropylium ions. When the pK R + values (5.70 × pK R + , kJ mol −1 ) of 15 cyclopropenylium and 21 tropylium ions were compared with the E red values (kJ mol −1 ), not one but eight correlation lines were shown within the range of slopes −0.25 to −1.05 for each of (1) 12 cyclopropenylium ions in 50% aqueous acetonitrile, (2) nine cyclopropenylium ions in 23% aqueous ethanol, (3) five cyclopropyl-substituted tropylium ions in 50% aqueous acetonitrile, (4) four t-butyl-substituted tropylium ions in 50% aqueous acetonitrile, (5) 10 tropylium ions in 23% aqueous ethanol, (6) nine polymethyl tropylium ions and others in 50% aqueous acetonitrile (7) six 1-aryl-8-tropylionaphthalenes in 50% aqueous ethanol, and (8) five bicycloalkanes fused with the tropylium ion in 50% aqueous ethanol. Thus, the pK R + scale, i.e. the water-affinity scale of the cations, is not generally interchangeable with the E red , i.e. an electron-affinity scale of the cations, even though the pK R + values in a single solvent were compared with the E red values (see categories (1),(3),(4) and (6)). The implications of such divergence of the pK R +- E red correlation are discussed.

Selective oxidation of tertiary-secondary vic-diols to α-hydroxy ketones by dioxiranes

Abstract Isolated dimethyldioxirane ( 1a ) and methyl(trifluoromethyl)dioxirane ( 1b ) efficiently afford the conversion of bicyclic diols bicyclo [2.2.2]octane-1,2-diol ( 2 ) and (+)-pinane-2,3-diol ( 6 ), of tricyclic diols adamantane-1,2-diol ( 3 ), homoadamantane-3,4-diol ( 4 ), and of homopentaprismane-3,4-diol ( 5 ) into the corresponding α-hydroxy ketones in high yields and under mild conditions. In the oxidation of (+)-pinane-2,3-diol ( 6 ), (−)-2-hydroxy-3-pinanone ( 11 ) is obtained in optical yield > 97% with retention of configuration.

Formation, properties, and reactions of the 1,2:3,4:5,6-tris(bicyclo[2.2.2]octeno)tropylium ion

Abstract The titled cation 4 has been synthesized and its properties and chemical reactivities investigated in detail. The cation 4 was shown to be formed in high yields not only by hydride abstraction from but also by the action of halogenoacetic acids upon the cycloheptatriene derivative 6 . Based on the results of UV-Vis and NMR spectroscopies together with iodometric analysis, this reaction was shown to proceed via protonation of 6 followed by dehydrogenation with molecular oxygen. The cation 4 was also shown to be formed by the action of rather weak Bronsted acids such as H 3 PO 4 , H 2 CO 3 , H 3 BO 3 , C 6 H 5 OH, and CH 3 NO 2 upon the 7-methoxycycloheptatriene 10 . These facts are in agreement with the extraordinarily high thermodynamic stability of 4 as is shown by its pK R + value, 13.0 (50% aqueous CH 3 CN, 25°C). The cation 4 does not show any reactivity towards the nucleophiles with the pK a of conjugate acid smaller than 10.3 except for the case of a slow reaction with CN − (pK a (NuH) 9.21). Also 4 does not react with the carbanions R − with pK a (RH) below 8.3, such as the tris(7H-dibenzo[c,g]fluorenylidenemethyl)methyl anion (Kuhns anion, C 67 H 39 -) and the 9-cyanofluorenyl anion, and a new hydrocarbon salt, 4 ·C 67 H 39 -, was isolated. In contrast, the reaction of 4 with the carbanions R − with pK a (RH) larger than 11, such as dicyanomethyl, α-cyano-p- nitrobenzyl, 1,1-dicyanoethyl, and dibenzo[c,g]fluorenyl anions, afforded the covalent compounds 4 -R. Whereas the compound 4 -R (as represented by the case of R=dibenzo[c,g]fluorenyl) only regenerated the cation 4 upon treatment with the trityl cation, the 7-methylcycloheptatriene 13 afforded the fully substituted cation 14 , which was found to be rather destabilized (pK R + 12.4) as compared with the hexasubstituted cation 4 .

Identification and functional characterization of nadrin variants, a novel family of GTPase activating protein for rho GTPases

Nadrin is a GTPase‐activating protein (GAP) for the rho family of GTPases that controls Ca2+‐dependent exocytosis in nerve endings. In this study, three novel splice variants of nadrin were identified and the variants were designated as nadrin‐102, ‐104, ‐116 and ‐126 according to their relative molecular masses. All nadrin variants share the GAP domain, coiled‐coil domain, serine/threonine/proline‐rich domain, SH3‐binding motif, and a successive repeat of 29 glutamines. Tissue distribution analyses using polyclonal antibodies that can discriminate each variant showed that the expression of nadrin‐102, ‐104 and ‐116 was dominant in neuronal tissues and correlates well with the differentiation of neurons while nadrin‐126 was strongly expressed in embryonic brain. Expression of nadrin‐116 in PC12 cells strongly inhibited NGF‐dependent neurite outgrowth and this effect was dependent on its GAP activity. In contrast, no significant effect on either cell morphology or neurite outgrowth was observed with other variants. All variants showed punctate appearance throughout the cytoplasm, while the 66‐kDa carboxyl‐terminal fragment of nadrin‐102 and/or nadrin‐116 was localized to the nucleus and its nuclear translocation was accelerated by NGF‐induced differentiation of the cells. These results suggested that nadrin variants are different in their ability to regulate rho‐mediated signaling and that, in addition to being aGTPase‐activating protein, nadrin‐102 and ‐116 have otherdistinct functions in the nucleus of the cell, implying apossible role in the cross‐talk between the cytoskeleton andthe nucleus.

Effects of t-butyl substituents on valence tautomerism of 7-t-butyl-7-cyano-1,3,5-cycloheptatrienes to the norcaradiene form

Abstract Introduction of t-butyl groups to the 2-, 3-, 2,4-, or 2,5-positions of 7-t-butyl-7-cyano-1,3,5-cycloheptatriene dramatically shifts the cycloheptatriene - norcaradiene equilibrium to the norcaradiene form. The nonbonded interaction is an important factor.

Synthesis, structure, and reduction of the cyclooctatetraene tetra-annelated with bicyclo[2.2.2]octene frameworks

Abstract The COT derivative 3 having rigid σ-frameworks has been newly synthesized and its X-ray structure determined; 3 is readily reduced to the dianion 32- in spite of severe steric hindrance.

Primary dependence of 7-aryl-2,5-di-t-butyl-1,3,5-cycloheptatriene valence tautomerism on the π-acceptor strength of the 7-aryl substituent

Abstract 13 C NMR studies showed that the population of the norcaradiene form of the title systems containing p-CH 3 O, H, and p-CF 3 on the 7-aryl group increases in this order. The result is consistent with the prediction from the π-acceptor strength of the aryl group estimated by INDO calculations.

Structural effects of the Grunwald–Winstein correlations in the solvolysis of some simple tertiary alkyl chlorides

The rates of solvolysis in various solvents at 25 °C were determined for five tertiary alkyl chlorides: 2-chloro-2,4,4-trimethylpentane (4), 2-chloro-2,4-dimethylpentane, 2-chloro-2-methylpentane, 1-chloro-1,3,3-trimethylcyclopentane (7) and 1-chloro-1-methylcyclopentane. The rate data were analysed on the basis of the original and extended Grunwald–Winstein-type equation [log(k/k0)=mYCl+c and log(k/k0)=lNT+mYCl+c] and the results were compared with those reported for 2-chloro-2-methylpropane (1) and 2-chloro-2,3,3-trimethylbutane (3). The rate data for 4 in 18 solvents give an excellent correlation with l=0·00±0·02 and m=0·74±0·01. The neopentyl group in 4 more effectively shields the rear-side of the reaction center than the tert-butyl group in 3 that is correlated by l=0·10±0·04 and m=0·81±0·04. The rate ratio between 4 and 1 at 25 °C is 275 in TFE and predicted to increase to 950 in TFA. The previous 4/1 rate ratio of 21 in 80% ethanol evidently underestimates the B-strain effect on the solvolysis rate of 4 by a factor of at least 40. The remote methyl groups in 7 works to increase rear-side shielding without increasing B-strain. The marked difference in the effect of the remote methyl groups between 4 and 7 suggests that the leaving chloride ion in 4 takes a locus that is nearly antiperiplanar to the tert-butyl group.