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| 1.
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Fujii, Tozo ; Ohba, Masashi ; Kawamura, Hitoshi ; Nakashio, Yoshiyuki ; Honda, Kei ; Matsubara, Satoshi
概要:
Both enantiomers [(1'R)-6 and (1'S)-6] of N6-(1,3-dimethyl-2- butenyl)adenine and their 9-β-D-ribofuranosides [(1''R)-16
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and (1''S)-16] have been synthesized for the first time from both enantiomers of alanine (15) in nine steps. These aglycones and nucleosides, together with N6-(3- methyl-2-butenyl)adenine (5) and its 9-β-D-ribofuranoside (18) as well as 9- β-D-ribofuranosyl-cis-zeatin (20) and 9-(2-deoxy-β-D-ribofuranosyl)-cis- zeatin (19), were tested for cytokinin activity in the tobacco callus bioassay. The order of their activity was 5> (1'R)-6 > (1''R)-16≃18>(1'S)- 6>(1''S)-16>20>19. The bioassay results are compared with those obtained previously for the derivatives modified analogously in the N6-substituent in the cis- and trans-zeatin series.
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| 2.
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Fujii, Tozo ; Yoshifuji, Shigeyuki ; Yoshida, Kiyoshi ; Ohba, Masashi ; Ikegami, Shiro ; Kirisawa, Makoto
概要:
The alkaline ferricyanide oxidation of the quaternary pyridinium salts (Ia-g) furnished pairs of the isomeric 2-pyridones (IIa-g) and 6-pyridones (IIIa-g) in good total yields. In all cases, the oxidation at the 2-position was much
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favored over that at the 6-position. The effect of the aryl group in the N-aralkyl chain on the orientation of the oxidation seemed to be negligibly small regardless of the number of the methylene groups separating the aryl group from the nitrogen. The extent of the 6-oxidation was slightly increased as the alkyl group at the 3-position was changed from the methyl to the ethyl group. The nuclear magnetic resonance spectra of these pyridones were measured in deuteriochloroform, carbon tetrachloride, and benzene-d_6. On the basis of the results summarized in Tables III-VI, the effects of the aryl group and the number of the methylene groups in the N-substituent on the chemical shifts for the pyridone-ring and neighboring group protons are discussed.
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| 3.
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Ohba, Masashi ; Izuta, Rie ; Shimizu, Emi
概要:
A full account of the total synthesis of two monoterpene alkaloids, (-)-plectrodorine [(-)-1] and (+)-oxerine [(+)-3], i
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s presented. The key steps involved are the formation of the oxazole alcohol 10 from the γ-butyrolactone 9 and the intramolecular Diels-Alder reaction of the oxazole-olefins 13a, b. Since the sign of specific rotation for the synthetic (+)-3 was different from that reported for natural oxerine, the absolute configuration of this alkaloid is not yet fully understood. © 2006 Pharmaceutical Society of Japan.
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| 4.
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Fujii, Tozo ; Ohba, Masashi ; Ali, Esahak ; Suzuki, Hitoshi ; Sakaguchi, Jun
概要:
The synthesis of (±)-9-demethylprotoemetinol [(±)-3d] was accomplished by LiAlH_4 reduction of the tricyclic ester (±)-5
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and subsequent debenzylation of the resulting tricyclic-alcohol (±)-10. Acetylation of (±)-3d with acetic anhydride and pyridine gave the diacetate (±)-11. The same sequence of reactions starting with (-)-5 afforded (-)-9-demethylprotoemetinol [(-)-3d] and the diacetate (-)-11 through (-)-10. Parallel synthetic routes starting with the isomeric tricyclic esters (±)-9 and (-)-9 produced (±)- and (-)-10-demethylprotoemetinols [(±)-4d and (-)-4d] and the corresponding diacetates [(±)-13 and (-)-13] through (±)-12 and (-)-12, respectively. The correctness of the structure and absolute stereochemistry of an Alangiutn alkaloid inferred to be 10-demethylprotoemetinol was confirmed by a direct comparison of its diacetate with synthetic (-)-13.
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| 5.
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Fujii, Tozo ; Yoshifuji, Shigeyuki ; Hatanaka, Yasumaru ; Yoshida, Kiyoshi ; Ohba, Masashi ; Yamada, Koichiro ; Ohkuma, Mihoko ; Shinoda, Hirotaka ; Mizuno, Denichi
概要:
Seventy-four compounds related to lactams and pyridones were synthesized and their anti-tumor activity was examined using Ehrlich carcinoma cells. 4-(2-Piperidyl) butyric acid hydrochloride was found to have some anti-tumor
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effect on the solid type of Ehrlich carcinoma cells, but no other substances were found to be effective. Correlation between the anti-tumor activity and structure of the tested compounds still remains uncertain.
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| 6.
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Fujii, Tozo ; Ohba, Masashi
概要:
The racemic synthesis of the Alangium lamarckii alkaloid 10-demethyltubulosine (2) has been accomplished for the first t
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ime via a "lactim ether route, "which included the intermediates (±)-7,(±)-8,(±)-10,and (±)-9. The 1'α-H isomers (±)-12 and (±)-11 were also obtained through this synthetic route. The assignments of the configuration at C-1'of (±)-2,(±)-9,(±)-11,and (±)-12 were based on four criteria, namely, the ratio of products from the catalytic reduction of (±)-10,thin-layer chromatographic mobility, and ^1H and ^<13>C nuclear magnetic resonance spectral features. The identity of synthetic (±)-2 with (-)-demethyltubulosine from A. lamarckii unequivocally established the structure of this alkaloid.
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| 7.
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Ohba, Masashi ; Tashiro, Takahiro
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Itaya, Taisuke ; Iida, Takehiko ; Natsutani, Itaru ; Ohba, Masashi
概要:
The relationship between the product patterns and the configurations of 1,2-cycloheptane- and 1,2-cyclooctanediols 9 in
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the cyclocondensations with oxalyl chloride in the presence of tricthylamine at 0°C has been shown analogous to that obtained for 1,2-disubstituted acyclic ethylene glycols 1: cis-1,2-cyclooctanediol (9f) produced the cyclic oxalate 14f as the major product, while trans-1,2-cycloheptanediol (9e) and trans-1,2-cyclooctanediol (9g) formed the cyclic carbonates 12e, g as the major products. On the other hand, the cyclic oxalates 14a-d were formed as the major products from 1,2-cyclopentane- and 1,2-cyclohexanediols regardless of the configuration. These results can be accounted for by assuming the boat-like transition states for cyclizations of the half esters of comparatively rigid five- and six-membered diols 9a-d. The cyclic oxalates 14a, c may be directly formed through the resulting tetrahedral intermediates from cis-diols (9a, c), and the cyclic carbonates 12a, c as the minor products after ring inversion of the tetrahedral intermediates. The tetrahedral intermediates from the trans-isomers 9b,d cannot undergo ring inversion, producing no traces of the cyclic carbonates 12b,d. © 2002 Pharmaceutical Society of Japan.
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| 9.
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Fujii, Tozo ; Ohba, Masashi ; Tachinami, Tsuyoshi ; Miyajima, Hisae
概要:
The first total synthesis of ochropposinine (1), a Neisosperma and Ochrosia alkaloid, has been accomplished in the form
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of a racemic modification by means of an initial coupling of the lactim ether (±)-3 with 5 and succeeding steps proceeding through the intermediates (±)-7,(±)-8,(±)-9,(±)-10,and (±)-11. A parallel synthetic route starting with (+)-3 produced the chiral target molecule (-)-1 via the intermediates (+)-7,(+)-8,(+)-9,10,and (-)-11. As a result, the absolute configuration of ochropposinine has been unequivocally established to be that represented by formula (-)-1.
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| 10.
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Fujii, Tozo ; Ohba, Masashi ; Akiyama, Shigeaki
概要:
In boiling 2.5 N solution of KOH in 40% (w/w) aqueous EtOH, the lactams (±)-5a, b, d were hydrolyzed to an extent of 75-
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98% within 8-20 h, attaining equilibrium with the corresponding ω-amino acid derivatives (±)-6a, b, d. The potassium salt (±)-8,generated in situ from the translactam acid (±)-7,was equilibrated with the ring-opened product (±)-6f and the recyclized cis isomer (±)-5f in a ratio of 57 : 15 : 28 within ca. 45 h under similar reaction conditions. The cis-N-(2-arylethyl) analog (-)-9 was converted into the trans-lactam acid (+)-13,a key synthetic precursor for the 8-hydroxy-9,10-dimethoxybenzo [a] quinolizidine-type Alangium alkaloids, through application of such alkaline hydrolytic cis-trans equilibration followed by debenzylation.
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