The C(7) Stereochemistry of the Chloroindolenines of Cleavamines and Quebrachamines

Wenkert, Ernest; Hagaman, Edward W.; Wang, Nai-yi; Kunesch, Nicole

doi:10.3987/r-1979-11-1439

Cited by 14 publications

(7 citation statements)

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“…The residue was purified by flash column chromatography (ether/hexane, 1/10) to give 20 mg (68%) of (−)-dehydroquebrachamine ( 55 ) as a light yellow gum. The 1 H NMR and 13 C NMR spectra of this sample were in agreement with those reported in the literature. 10b,50b …”

Section: Experimental Section51supporting

confidence: 90%

“…One strength of our strategy is that it provides easy access to many different members of this family through advanced intermediates in the synthetic sequence. As a demonstration of this, the pentacyclic intermediate ent - 43 was converted into (+)-aspidospermidine ( 53 ), 34d, (−)-quebrachamine ( 54 ), 10c,48r,s, and (−)-dehydroquebrachamine ( 55 ) (Scheme ). 10b,49d, The reduction of the imine double bond of ent - 43 with NaBH 4 in EtOH to dehydroaspidospermidine followed by hydrogenation of the olefin with Pt 2 O in EtOH afforded natural (+)-aspidospermidine ( 53 ) in 73% yield. Treatment of ent - 43 with NaBH 3 CN in AcOH accomplished the fragmentation of the C-7−C-21 bond and the chemoselective reduction of the resulting iminium ion to yield (−)-dehydroquebrachamine ( 55 ) in 68% yield.…”

Section: Resultsmentioning

confidence: 99%

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An Efficient Approach to Aspidosperma Alkaloids via [4 + 2] Cycloadditions of Aminosiloxydienes: Stereocontrolled Total Synthesis of (±)-Tabersonine. Gram-Scale Catalytic Asymmetric Syntheses of (+)-Tabersonine and (+)-16-Methoxytabersonine. Asymmetric Syntheses of (+)-Aspidospermidine and (−)-Quebrachamine

et al. 2002

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Described is a concise, highly stereocontrolled strategy to the Aspidosperma family of indole alkaloids, one that is readily adapted to the asymmetric synthesis of these compounds. The strategy is demonstrated by the total synthesis of (+/-)-tabersonine (rac-1), proceeding through a 12-step sequence. The basis for this approach was provided by a highly regio- and stereoselective [4 + 2] cycloaddition of 2-ethylacrolein with 1-amino-3-siloxydiene developed in our laboratory. Subsequent elaboration of the initial adduct into the hexahydroquinoline DE ring system was accomplished efficiently by a ring-closing olefin metathesis reaction. A novel ortho nitrophenylation of an enol silyl ether with (o-nitrophenyl)phenyliodonium fluoride was developed to achieve an efficient, regioselective introduction of the requisite indole moiety. The final high-yielding conversion of the ABDE tetracycle into pentacyclic target rac-1 relied on intramolecular indole alkylation and regioselective C-carbomethoxylation. Our approach differs strategically from previous routes and contains built-in flexibility necessary to access many other members of the Aspidosperma family of indole alkaloids. The versatility of the synthetic strategy was illustrated through the asymmetric syntheses of the following Aspidosperma alkaloids: (+)-aspidospermidine, (-)-quebrachamine, (-)-dehydroquebrachamine, (+)-tabersonine, and (+)-16-methoxytabersonine. Of these, (+)-tabersonine and (+)-16-methoxytabersonine were synthesized in greater than 1-g quantities and in enantiomerically enriched form ( approximately 95% ee). The pivotal asymmetry-introducing step was a catalyzed enantioselective Diels-Alder reaction, which proceeded to afford the cycloadducts in up to 95% ee. Significantly, the synthetic sequence was easy to execute and required only four purifications over the 12-step synthetic route.

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Section: Experimental Section51supporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

An Efficient Approach to Aspidosperma Alkaloids via [4 + 2] Cycloadditions of Aminosiloxydienes: Stereocontrolled Total Synthesis of (±)-Tabersonine. Gram-Scale Catalytic Asymmetric Syntheses of (+)-Tabersonine and (+)-16-Methoxytabersonine. Asymmetric Syntheses of (+)-Aspidospermidine and (−)-Quebrachamine

et al. 2002

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“…As a result, seven new ( 1 – 7 ) and 24 known alkaloids were identified. The known alkaloids were identified as ervachinine C, ervachinine A, ervachinine B, tabernaecorymbosine A, tabernaecorymbosine B, cononitarine B, conofoline, conophylline, hydroxyindolenine, voacangine hydroxyindolenine, voacristina hydroxyindolenina, 3-(2-oxopropyl)voacangine, voacristina, ibogaine, voacristine, tabernanthine, isovoacangine, 19-epi-isovoacristine, 19 S -heyneanine, 1-methylvoaphylline, voaphyllinediol, 19,20- E -vallesamine, and picrinine . The cytotoxicity of these compounds against five human cancer cell lines was evaluated.…”

mentioning

confidence: 99%

Cytotoxic Indole Alkaloids from Tabernaemontana divaricata

et al. 2013

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Five new vobasinyl-ibogan-type bisindole alkaloids, tabernaricatines A-E (1-5), two new monomers, tabernaricatines F and G (6 and 7), and 24 known indole alkaloids were isolated from the aerial parts of Tabernaemontana divaricata. Alkaloids 1 and 2 are the first vobasinyl-ibogan-type alkaloids possessing a six-membered ring via an ether linkage between C-17 and C-21. All compounds except for 3 were evaluated for their cytotoxicity against five human cancer cell lines; conophylline showed significant bioactivity against HL-60, SMMC-7721, A-549, MCF-7, and SW480 cells with IC₅₀ values of 0.17, 0.35, 0.21, 1.02, and 1.49 μM, respectively.

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“…Nine indole alkaloids have been isolated from the roots of Ervaramia yunnanensis. Eight of them are known and identified as: heyneanine (1), ibogamine (2), coronaridine (3), voacanginge (4), voacanginge hydroxyindolenine (5), ibogaine (6), (+)-minovincinine (7), and voachalotin (8) (3) while the last one is a new compound, for which we propose the name ervayunine (9).…”

Section: Resultsmentioning

confidence: 99%