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| 1.
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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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| 2.
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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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| 3.
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Fujii, Tozo ; Ohba, Masashi
概要:
With the aim of establishing the structure of the Alangium alkaloid desmethylpsychotrine, stereospecific syntheses of tw
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o alternative structures, (±)-9-demethylpsychotrine (1) and (±)-10-demethylpsychotrine (2), have been achieved through a"lactim ether route."The synthesis of (±)-1 started with an initial condensation of the lactim ether 6,derived from the translactam ester 5,with 3-benzyloxy-4-methoxyphenacyl bromide (7a) and proceeded through the intermediates 8a, 9a, 10c, 10a, 11a, 12a, 13a, 14a, and 15a. A parallel sequence of conversions starting with 6 and 4-benzyloxy-3-methoxyphenacyl bromide (7b) produced (±)-2. The ^<13>C nuclear magnetic resonance spectra of (±)-1 and (±)-2 confirmed their endocyclic double bond structure in the dihydroisoquinoline moiety. Spectral comparison of (±)-1 and (±)-2 with natural desmethylpsychotrine suggested formula 1 to be the most likely structure of this alkaloid.
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| 4.
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Fujii, Tozo ; Ohba, Masashi ; Tachinami, Takeshi ; Ohashi, Takako
概要:
A full account is given of the first racemic and chiral syntheses of 11-methoxydihydrocorynantheol [(-)-1], a candidate
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structure for the Neisosperma alkaloid ochromianine. Coupling of (±)-trans-6-ethoxy-3-ethyl-2,3,4,5-tetrahydro-4-pyridineacetic acid ethyl ester [(±)-6] with 2-chloro-1-(6-methoxy-1H-indol-3-yl)ethanone (4) in the presence of KBr produced the lactam ketone (±)-7,which was then converted into the lactam (±)-9 through the oxazolium salt (±)-8. Bischler-Napieralski cyclization of (±)-9 followed by catalytic hydrogenation gave the tetracyclic ester (±)-11. On reduction with LiAlH_4,(±)-11 yielded the racemic target (±)-1. A parallel synthetic route starting from (+)-6 and 4 afforded the chiral target (-)-1 via (+)-7,8,(+)-9,and (-)-11. Identity of synthetic (-)-1 with ochromianine unequivocally established the structure and absolute stereochemistry of this alkaloid.
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| 5.
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Fujii, Tozo ; Ohba, Masashi ; Seto, Shigeki
概要:
A detailed account is given of the first chiral synthesis of the Ophiorrhiza alkaloid ophiorrhizine [(-)-1]. The synthes
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is was started by coupling the lactim ether (+)-4, readily available from cincholoipon ethyl ester [(+)-3], with 6-benzyloxy-3-chloroacetylindole (6) to form the lactam ketone (+)-8 and proceeded through the intermediates (+)-9, (+)-10, 11, (-)-12, (-)-13, 14, (-)-15, and (-)-16. The identity of synthetic (-)-1·H2O with natural ophiorrhizine unequivocally established the absolute stereochemistry of this alkaloid.
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| 6.
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Fujii, Tozo ; Ohba, Masashi
概要:
In order to establish the structure of the Alangium alkaloid demethylcephaeline, chiral syntheses of the two possible alternative structures, (-)-9-demethylcephaeline (1) and (-)-10-demethylcephaeline (2), have been
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accomplished through a "cincholoipon-incorporating route." The synthesis of (-)-2 started with an initial condensation of the tricyclic acid (-)-12b, prepared from the ester (-)-11b by alkaline hydrolysis, with 3-benzyloxy-4-methoxyphenethylamine and proceeded through the intermediates (-)-13b, (+)-15b, and (-)-14b. The 1'-epimers (-)-18b and (-)-17 were also produced in this reaction sequence. A parallel sequence of conversions starting with (+)-15a afforded (-)-1 via the intermediate (-)-14a, together with the 1'-epimer (-)-16 via (-)-18a. Unfortunately, however, lack of a sufficient amount of natural (-)-demethylcephaeline for a detailed and direct comparison precluded identification of either (-)-1 or (-)-2 with this alkaloid, leaving its chemistry incomplete.
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| 7.
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Fujii, Tozo ; Ohba, Masashi ; Yoneyama, Kaoru ; Kizu, Hiroko ; Yoshifuji, Shigeyuki
概要:
A formal chiral synthesis of the Alangium alkaloid (-)-ankorine [(-)-6] has been accomplished in the form of the synthesis of the lactam phenol (+)-14 from the (+)-trans-lactim ether (+)-5 and 2-benzyloxy-3,4-dimethoxyphenacyl bromide
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through the intermediates (+)-10 and 11. A parallel sequence of conversions starting from the (-)-trans-lactim ether (-)-5 and proceeding through the intermediates (-)-10,24,(-)-14,(-)-15,26,(+)-27,and (+)-28 produced the enantiomer [(+)-6] of natural ankorine. For an alternative chial synthesis of (-)-6,ethyl cincholoiponate [(+)-19] was acetylated and the resulting N-acetyl derivative (+)-20-was oxidized with RuO_4 to give the 6-piperidone (+)-21,and 2-piperidone (-)-23 in 55% and 27% yields, respectively. The (-)-cis-lactim ether (-)-16,obtained by ethylation of (+)-21 with triethyl-oxonium fluoroborate, was then converted into (-)-13,a known precursor for the synthesis of (-)-ankorine [(-)-6], in good overall yield by a "lactim ether route, " which proceeded through (+)-15 and 12.
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| 8.
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Fujii, Tozo ; Ohba, Masashi
概要:
With a view to establishing the structure of the Alangium alkaloid desmethylpsychotrine, (+)-9-demethylpsychotrine [(+)-1] has been synthesized from ethyl cincholoiponate [(+)-6] and 3-benzyloxy-4-methoxyphenacyl bromide by
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the "cincholoipon-incorporating method" through the intermediates (+)-7,8,10-(+)-14,and (+)-17-(+)-22. The identity of synthetic (+)-1 with natural desmethylpsychotrine unequivocally established the structure of this alkaloid.
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| 9.
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Ohba, Masashi ; Hayashi, Mitsuko ; Fujii, Tozo
概要:
The first total synthesis of the Alangium vitiense alkaloid 9-demethyltubulosine (1) has been achieved in the form of a
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racemic modification through a"lactim ether route, " which included the intermediates (±)-7,(±)-8,(±)-10,and (±)-9. The 1'α-Hisomers (±)-12 and (±)-11 were also produced through this synthetic route. On the other hand, the nonconformity of synthetic (±)-1 with another (-)-demethyltubulosine from A. lamarckii indicated the alternative 10-demethyl structure (2) to be correct for the A. lamarckii alkaloid. The assignments of the configuration at C-1' of (±)-1,(±)-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.
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| 10.
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Fujii, Tozo ; Kogen, Hiroshi ; Yoshifuji, Shigeyuki ; Ohba, Masashi
概要:
The first total synthesis of the Alangium alkaloid alangimarckine (8) has been accomplished in the form of a racemic mod
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ification by means of an initial coupling of the (±)-tricyclic amino acid 6 with tryptamine and succeeding steps proceeding through the intermediates (±)-7,(±)-10,and (±)-9. The 1'-epimers (±)-12 and (±)-11 were also produced in this reaction sequence. A parallel sequence of conversions starting with the (-)-tricyclic amino acid 6 yielded the chiral molecule (-)-8 via the intermediates (+)-7,(+)-10,and (+)-9,together with the 1'-epimer (-)-11 via (-)-12. The identity of the synthetic (-)-8 with natural alangimarckine unequivocally established the structure and absolute configuration of this alkaoid. The assignments of the configuration at C-1'of 8,9,11,and 12 were based on five criteria, namely, the ratio of products from the NaBH_4 reduction of (±)-10,thin-layer chromatographic mobility, and proton and carbon-13 nuclear magnetic resonance and circular dichroism spectroscopic features.
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