Biomedical subjects

Tomohiko Ohwada

Publications and source records attributed to Tomohiko Ohwada.

24 records · Page 2Linked to original sources

PubMed2002

Generation of functionalized asymmetric benzynes with TMP-zincates. Effects of ligands on selectivity and reactivity of zincates.

We have developed new methods for preparing functionalized benzynes through deprotonative zincation as a key reaction using R2Zn(TMP)Li, and we also describes dramatic ligand effects on the benzyne formation. Deprotonative zincation of various meta-substituted bromobenzenes with Me2Zn(TMP)Li proved effective for the one-pot generation of various 3-functionalized benzynes, particularly those electrophilic substituents such as ester, amide, and cyano. On the other hand, zincation with tBu2Zn(TMP)Li, followed by electrophilic trapping (with I2) proved a powerful tool for the preparation of 1,2,3-trisubstituted aromatic compounds.8 The resultant 1,2,3-trisubstituted benzenes are available as precursors for generation of 3-substituted benzynes by halogen-zinc exchange reactions with Me3ZnLi. These methods offer far greater generality than previous methods for the synthesis of functionalized asymmetric benzynes, and should be of value in new syntheses of various natural products and functional materials. In addition, these results underline the utility of spectator ligands on the central metal of ate complexes as a tunable functionality in the development of new ate complex-promoted reactions.

Journal Article↗

PubMed2002

Mutagenicity of aristolochic acid in the lambda/lacZ transgenic mouse (MutaMouse).

Aristolochic acid (AA) is found in a plant that causes urothelial carcinomas in patients with Chinese herb nephropathy (CHN). To evaluate the in vivo mutagenicity of AA, we analysed the mutant frequency (MF) in the lacZ and cII gene of 10 organs of the lambda/lacZ transgenic mouse (MutaMouse) after intragastric treatment with AA (15mg/kg per week x 4). Simultaneously, the clastogenicity of AA was evaluated by the peripheral blood micronucleus assay. The nature of the mutations induced by AA was revealed by the sequence analysis of the cII gene, which is also a phenotypically selectable marker in the lambda transgene. MFs in the target organs-forestomach, kidney, and bladder of AA-treated mice were significantly higher than those of control mice (forestomach 33- and 15-fold; kidney 10- and 9-fold; bladder 16- and 31-fold, for the lacZ and cII, respectively). The MFs in non-target organs, except the colon, showed only slight increases. Sequence analysis of cII mutants in target organs revealed that AA induced mainly A:T to T:A transversions whereas G:C to A:T transitions at CpG sites predominated among spontaneous mutations. These results suggested that AA, which is activated by cytochrome P450 and peroxidase to form cyclic nitrenium ions that bind to deoxyadenine, caused the A to T transversions in the target organs of mice.

Animals↗

PubMed2002

Dinitropyrenes induce gene mutations in multiple organs of the lambda/lacZ transgenic mouse (Muta Mouse).

Dinitropyrenes (DNPs), 1,3-, 1,6- and 1,8-dinitropyrene, are carcinogenic compounds found in diesel engine exhaust. DNPs are strongly mutagenic in the bacterial mutation assay (Ames test), mainly inducing frameshift type mutations. To assess mutagenicity of DNPs in vivo is important in evaluating their possible involvement in diesel exhaust-induced carcinogenesis in human. For this purpose, we used the lambda/lacZ transgenic mouse (Muta Mouse) to examine induction of mutations in multiple organs. A commercially available mixture of DNPs (1,3-, 1,6-, 1,8-, and unidentified isomer (s) with a content of 20.2, 30.4, 35.2, and 14.2%, respectively) was injected intragastrically at 200 and 400mg/kg once each week for 4 weeks. Seven days after the final treatment, liver, lung, colon, stomach, and bone marrow were collected for mutation analysis. The target transgene was recovered by the lambda packaging method and mutation of lacZ gene was analyzed by a positive selection with galE(-) E. coli. In order to determine the sequence alterations by DNPs, the mutagenicity of the lambda cII gene was also examined by the positive selection with hfl(-) E. coli. Since cII gene (294bp) is much smaller than the lacZ (3024bp), it facilitated the sequence analysis. Strongest increases in mutant frequencies (MFs) were observed in colon for both lacZ (7.5x10(-5) to 43.3x10(-5)) and cII (2.7x10(-5) to 22.5x10(-5)) gene. Three-four-fold increases were observed in stomach for both genes. A statistically significant increase in MFs was also evident in liver and lung for the lacZ gene, and in lung and bone marrow for the cII gene. The sequence alterations of the cII gene recovered from 37 mutants in the colon were compared with 50 mutants from untreated mice. Base substitution mutations predominated for both untreated (91%) and DNP-treated (84%) groups. The DNPs treatment increased the incidence of G:C to T:A transversion (2-43%) and decreased G:C to A:T transitions (70-22%). The G:C to T:A transversions, characteristic to DNPs treatment, is probably caused by the guanine-C8 adduct, which is known as a major DNA-adduct induced by DNPs, through an incorporation of adenine opposite the adduct ("A"-rule). The present study showed a relevant use of the cII gene as an additional target for mutagenesis in the Muta Mouse and revealed a mutagenic specificity of DNPs in vivo.

Animals↗

PubMed2002

Molecular basis of pimarane compounds as novel activators of large-conductance Ca(2+)-activated K(+) channel alpha-subunit.

Effects of pimaric acid (PiMA) and eight closely related compounds on large-conductance K(+) (BK) channels were examined using human embryonic kidney (HEK) 293 cells, in which either the alpha subunit of BK channel (HEKBKalpha) or both alpha and beta1 (HEKBKalphabeta1) subunits were heterologously expressed. Effects of these compounds (10 microM) on the membrane potential of HEKBKalphabeta1 were monitored by use of DiBAC(4)(3), a voltage-sensitive dye. PiMA, isopimaric acid, sandaracoisopimaric acid, dihydropimaric acid, dihydroisopimaric acid, and dihydroisopimarinol induced substantial membrane hyperpolarization. The direct measurement of BKalphabeta1 opening under whole-cell voltage clamp showed that these six compounds activated BKalphabeta1 in a very similar concentration range (1-10 microM); in contrast, abietic acid, sclareol, and methyl pimarate had no effect. PiMA did not affect the charybdotoxin-induced block of macroscopic BKalphabeta1 current. Single channel recordings of BKalphabeta1 in inside-out patches showed that 10 microM PiMA did not change channel conductance but significantly increased its open probability as a result of increase in sensitivity to Ca(2+) and voltage. Because coexpression of the beta1 subunit did not affect PiMA-induced potentiation, the site of action for PiMA is suggested to be BKalpha subunit. PiMA was selective to BK over cloned small and intermediate Ca(2+) activated K(+) channels. In conclusion, PiMA (>1 microM) increases Ca(2+) and voltage-sensitivity of BKalpha when applied from either side of the cell membrane. The marked difference in potency as BK channel openers between PiMA and abietic acid, despite only very small differences in their chemical structures, may provide insight into the fundamental structure-activity relationship governing BKalpha activation.

Abietanes↗

PubMed1996

Superacid-Catalyzed Reaction of Substituted Benzaldehydes with Benzene.

Benzaldehydes bearing an electron-withdrawing group reacted with 2 equiv of benzene in the presence of a superacid, trifluoromethanesulfonic acid, to give substituted triphenylmethane in good yields. On the other hand, benzaldehydes bearing an electron-donating or a neutral group reacted under the similar conditions to give unsubstituted diphenylmethane and triphenylmethanol, together with substituted benzene. We propose a new mechanism of this reaction, which involves transalkylation as the key step.

Journal Article↗

PubMed1996

Orbital Unsymmetrization Affects Facial Selectivities of Diels-Alder Dienophiles.

We investigated the Diels-Alder reactions of maleic anhydrides embedded in a dibenzobicyclo[2.2.2]octatriene motif as a nonsterically biased dienophile. Substituents on a benzene ring in these dienophiles are far from the reaction center, providing a sterically equivalent pi-face. Instead substituents can unsymmetrize the dienophilic pi face through pi (anhydride)-pi (aromatic) orbital interactions. Electron-withdrawing substituents affect the facial bias and relative rates of these cycloadditions. The preference of the cycloadditions is opposite in direction to those observed in nucleophilic additions of 2-substituted-9,10-dihydro-9,10-ethanoanthracen-11-ones (dibenzobicyclo[2.2.2]octadienones) and in electrophilic additions of 2-substituted 9,10-dihydro-9,10-ethenoanthracenes (dibenzobicyclo[2.2.2]octatrienes), though all of them have related dibenzobicyclic systems.

Journal Article↗