- Synthesis of vinca alakaloids and realated compounds 98 [1]. Oxidation with dimethyldioxirane of compounds containing the aspidospermane and quebrachamine ring system. A simple synthesis of (7s,20S)-(+)-rhazidigenine and (2R,7S,20S)-(+)-rhazidine
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The oxidation of (-)-tabersonine (1) with dimethyldioxirane (DMD) in neutral and acidic medium gave 16-hydroxytabersonine-N-oxide (3) and the didehydrovincamine isomers 4 and 5, respectively. (+)-14,15-Didehydro-quebrachamine (7) furnished the hydroxyindolenine 9, and the pentacyclic derivative 11. (+)- Quebrachamine (8) and DMD in neutral medium gave (7S,20S)-(+)-rhazidigenine (12) which was converted to (2R,7S,20S)-(+)-rhazidine (13b) with hydrochloric acid.
- Eles, Janos,Kalaus, Gyoergy,Levai, Albert,Greiner, Istvan,Kajtar-Peredy, Maria,Szabo, Pal,Szabo, Lajos,Szantay, Csaba
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- Oxidation of β-Anilinoacrylate Alkaloids Vincadifformine and Tabersonine by Fremy's Salt. A Mechanistic Insight into the Rearrangement of Aspidosperma to Hunteria Alkaloids
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β-Anilinoacrylate Aspidosperma alkaloids vincadifformine (2a) and tabersonine (2b) react with Fremy's salt in aqueous acidic conditions via radical coupling at C-16.The resulting zwitterionic compounds 7a and 10 rearange to isoxazolidines 8 and then ultimately to azepinoindoles 9.The mechanism of these reactions is discussed, and the structures of 7a, 8b, and 9a were established by single-crystal X-ray analysis.Diazotization of amine 20b (X = NH2) affords fragmentation-cyclization products corresponding to eburnanes 18 and 21.This reaction mimics the skeletal rearrangement of Aspidosperma -> Hunteria alkaloids, and these findings support Wenkert's biogenetic proposal.
- Palmisano, Giovanni,Danieli, Bruno,Lesma, Giordano,Trupiano, Federica,Pilati, Tullio
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- Synthesis of 18-hydroxyvincamines and epoxy-1,14-secovincamines; A new proof for the aspidospermane-eburnane rearrangement
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Chemical transformations started from tabersonine were studied. A one-pot oxidative ring-transformation with permaleic acid in methanol yielded 17,18-dehydrovincamine. Hydroboration-oxidation of the latter compound led to alkaloid 17,18-dehydrovincamone. Hydroboration-oxidation of tabersonine resulted 14β-hydroxyvincadifformine and 15β-hydroxyvincadifformine. Allowing 14β- and 15β- hydroxyvincadifformines to react with permaleic acid/methanol provided 1,14-secovincamines, serving as new evidence for the mechanism of the aspidospermane-eburnane transformation. On the other hand 18β-hydroxyvincamine was obtained from 14β-hydroxyvincadifformine by reaction with 3-chloroperbenzoic acid and successive treatment with triphenylphosphine/aqueous acetic acid.
- Nemes, Andras,Szantay Jr., Csaba,Czibula, Laszlo,Greiner, Istvan
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p. 2347 - 2362
(2008/09/18)
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- Dye-sensitized Photo-oxygenation of the Aspidosperma Alkaloids Vincadifformine and Tabersonine. A New, Convenient Approach to Vincamine
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The dye-sensitized photo-oxygenation of (-)-vincadifformine (1) and (-)-tabersonine (3) is discribed.Reaction takes place through the intermediate formation of 16-hydroperoxyindolenines, which decompose to give 2,16-seco-products or which can be efficently trapped by reductants to give a new stereoselective synthesis of the 16-hydroxy-indoles (10) and (14).These compounds are the key precursors to the eburnane alcaloids vincamine (4) and Δ14-vincamine (6).Suitable experimental conditions give compounds (4) and (6) in good yields directly from their Aspidosperma precursor.
- Calabi, Luisella,Danieli, Bruno,Lesma, Giordano,Palmisano, Giovanni
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p. 1371 - 1380
(2007/10/02)
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- Ozonation in Alkaloid Chemistry: a Mild and Selective Conversion of Vincadifformine into Vincamine
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Vincamine has been obtained in a 'one-pot' method by ozonation of vincadifformine.
- Danieli, Bruno,Lesma, Giordano,Palmisano, Giovanni,Gabetta, Bruno
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p. 908 - 909
(2007/10/02)
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- AROMATIC SUBSTITUTION EFFECTS IN THE ASPIDOSPERMANE-EBURNANE REARRANGEMENT OF INDOLE ALKALOIDS
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The influence of substitutions in aromatic part of indole alkaloids with aspidosperma skeleton on their rearrangement into products with eburnane-type structure is studied.Results are applied to vincamine derivatives.
- Lewin, Guy,Rolland, Yves,Poisson, Jacques
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p. 1915 - 1920
(2007/10/02)
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