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| 1.
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論文
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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
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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| 3.
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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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| 4.
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Fujii, Tozo ; Ohba, Masashi ; Hatakeyama, Hiroshi
概要:
The chiral synthesis of (-)-9-demethyltubulosine [(-)-1] has been achieved for the first time via a "cincholoipon-incorporating route," which started from cincholoipon ethyl ester [(+)-7] and passed through the intermediates (-)-8,
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(-)-9, (+)-10, and (-t-)-11. As a result, the absolute configuration of the Alangium vitiense alkaloid 9-deniethyltubulosine has been unequivocally established to be that represented by formula (-)-1.
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| 5.
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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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| 6.
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論文
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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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| 7.
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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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