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K Takemoto

Publications and source records attributed to K Takemoto.

At least 127 records · Page 7Linked to original sources
PubMed1984

Syntheses based on the tautomerism of purine and pyrimidine derivatives.

Synthetic applications of the tautomerism based on purine and pyrimidine derivatives were investigated. Particularly, chloropyrimidine derivatives, which were reactive enough to go back to the more stable lactam form, were used for dehydration and desulfhydration. Alkoxypyrimidines were thermally cleaved to give olefins or esters, together with the lactim to lactam transformation. The extrusion of alkylthio group from thioalkyl purines or pyrimidines took place under bacic conditions to give olefin, indicating another tautomeric transformation.

Indicators and Reagents↗
PubMed1984

Interrelationship between tumorigenicity and the chemical nature of N-methyl-N'-aryl-N-nitrosoureas.

The tumorigenic activity of a series of N-methyl-N'-aryl-N-nitrosoureas (I-X) on mouse skin was investigated in comparison with that of N-methyl-N-nitrosourea (MNU). The tumorigenic potency of I-X was less than that of MNU, although the former are much stronger mutagens; and no correlations were found between the tumorigenicity of I-X and their mutagenicity. The major tumors induced by the methoxy and methyl derivatives, both of which have high lipophilicity, were sarcomas (fibrosarcomas and fibroanaplastic, anaplastic, and pleomorphic cell sarcomas) in contrast to the fact that squamous cell carcinomas were the major tumors induced by MNU. Although the nitrosoureas were not administered intragastrically to the animals, squamous cell carcinomas were observed in the forestomachs of mice treated with I-X, but no tumors were produced in the stomachs by MNU. Adenocarcinomas were found in the lungs of mice treated with all the nitrosoureas. Hyperplastic nodules were observed in the livers of mice treated with methoxy and hydrogen derivatives, while cysts were found with methyl derivatives.

Alkylation↗
PubMed1983

[Effects of chromium compounds on the respiratory system. 2. Difference between water-soluble hexavalent and trivalent compounds].

Transference and transformation of chromium compounds, known as occupational carcinogens, in the lung of rats were studied by determining blood chromium levels after a single mist inhalation or an intravenous injection of water-soluble chromic acid (hexavalent) and chromium chloride (trivalent). Conclusion drawn from this study are as follows: Transference of chromium from the lung to the blood stream is ended quickly after the inhalation of chromic acid mist. Alveolar permeability of hexavalent chromic acid is much higher than that of trivalent chromium chloride. The greater part of the transferred chromium in the blood after the inhalation of chromic acid mist is not transformed to any other form; therefore, it seems to be present as the hexavalent form. The hexavalent chromic acid in the blood diffused to the liver, kidneys and the spleen, but the trivalent chromium chloride distributed only in the blood. The hexavalent chromic acid in the blood decreased more slowly than the trivalent chromium chloride. The biological half-time of the chromic acid in the blood was about 60 hours, whereas that of the chromium chloride was only about 2 hours. These results suggest that the water-soluble hexavalent chromium compounds may be apparently different from the trivalent chromium compounds in the transference from the lung and following distribution in the body. These differences might be caused by the high permeability through the cell membrane in hexavalent chromium compounds and the high possibility of binding with proteins in trivalent chromium compounds.

Aerosols↗
PubMed1983

Photoreaction of poly(amino acid)s containing thymine moieties as side groups.

The photodimerization reaction of thymine bases in poly-D,-L,and -DL-lysine and isopoly-L-lysine derivatives containing thymine bases was studied over a wide range of pH in aqueous buffered solution. It was found that the quantum yield of the intramolecular photodimerization of grafted thymine bases was affected by the conformation of the polymer in solution: alpha-helix or random coil. And the helical conformation was found to be favorable to cause the photodimerization of thymine bases. The photodimerization of the grafted thymine bases in poly-D, and -L-lysine derivatives caused to increase of the helix content of the poly-lysines, because the photodimer of thymine bases fixed alpha-helix of the polymer main chain.

Photochemistry↗
PubMed1982

[Thin-section CT scan of the pituitary gland (author's transl)].

Topographic anatomy of the pituitary fossa was studied by 2 mm thin-section CT scan (Somatom II). Nineteen with normal pituitary (control group) and 20 with suspected pituitary abnormality were selected. Plain and contrast CT were performed in all cases. Contrast CT was carried out immediately after the rapid infusion of 220 ml of 30% iodinated contrast medium. In all of control group but two, pituitary gland was detected as homogenous density and its density was as same as density of normal brain tissues, and was enhanced in degree of about 25 CT number. In 2 cases, small low density was visualized in the pituitary gland. Pituitary gland was differentiated from cavernous sinus was usually higher than the pituitary gland. In abnormal group, the microadenoma of the pituitary gland was diagnosed in 5 cases and 3 out of 5 cases was proved by surgery. All 3 microadenomas proved slightly dense by plain CT and enhanced higher than normal pituitary gland by contrast CT. Polytomograms showed no abnormality of the sella turcica in one of these 3 cases. Although 3 microadenomas were detected by the abnormal enhancement, we are not sure whether all of microadenoma can be detected by CT alone. Arachnoid herniation into the pituitary fossa was diagnosed in 7 of control group and 2 of abnormal group. Four out of these 9 cases were verified by using Metrizamide CT. By plain thin-section CT, the diagnosis of arachnoid herniation seems to be possible without Metrizamide CT.

Adenoma↗
PubMed1982

[Computed tomography in brain metastases (author's transl)].

CT scan of the one hundred and sixteen metastatic brain tumors in 50 patients was reviewed and compared to the previous reports. The most common primary organ was lung (43%) followed by breast (18%), colon (10%) and kidney (6%). Solitary nodule was found in 20 patients (40%). On plain CT scan, tumor nodules were demonstrated as slightly high density in 38 (33%), isodensity in 50 (43%) and slightly low density in 28 (24%). Majority of tumor nodules were present in the corticomedullary junction (82%). Brain edema seen as a peritumoral low density was extensive in comparison with the edema in the glioma of the similar size. On contrast CT scan, ring like enhancement was seen in 41 (35%). Intra-tumoral bleeding was shown in 2 metastatic nodules from choriocarcinoma and in one metastatic nodule from renal cell carcinoma. All 3 cases were proved by surgery or autopsy.

Adult↗
PubMed1982

Intramolecular interaction of thymine and adenine bases in synthetic oligo- and polynucleotide models.

Four types of oligomer systems, ranging from monomers to hexamers, of linear polyethyleneimine derivatives having pendant thymine or adenine bases were prepared. In order to evaluate the intramolecular interaction between the pendant nucleic acid bases, ultraviolet spectra at various pH regions and proton NMR spectra at various temperatures were measured. The results on UV hypochromicities and pKa values led to the clarification of such interaction between the bases: adenine bases can be prone to interact intramolecularly by stacking, while the interaction between thymine bases is not due to stacking, but due only to residual interaction which takes place between neighboring chromophores.

Adenine↗
PubMed1981

Postcontrast computed tomography in subarachnoid hemorrhage from ruptured aneurysms.

Computed tomography (CT) scans of 49 patients with subarachnoid hemorrhage (SAH) secondary to ruptured aneurysms were reviewed. Subarachnoid blood was detected in 95% when CT was performed within 5 days after the bleeding. Prediction of the site of the ruptured aneurysm from distribution of the cisternal blood varied from 92% for the anterior cerebral artery aneurysms to 70% for the middle cerebral and 47% for the internal carotid artery aneurysms. Following plain CT scans, postcontrast studies were performed in 27 patients. Aneurysms were directly visualized in 8 cases and subarachnoid enhancement was noted in 21. In 3 cases, subarachnoid enhancement made possible a correct diagnosis of SAH in the absence of evidence of cisternal blood on precontrast CT scans.

Adult↗