Absolute configuration of the iboga and voacanga alkaloids : chiroptical approach

Bláha, K.; Koblicová, Z.; Trojánek, J.

doi:10.1016/s0040-4039(01)84927-3

Cited by 22 publications

(17 citation statements)

References 10 publications

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“…It is notable that our synthetic solution provided the enantiomers of each aforementioned secondary metabolite because of the interestingly enantiomeric absolute configuration of the natural (+)-catharanthine (3) with respect to other iboga alkaloids. 53 The synthesis of unnatural (À)-catharanthine (3) 54 and further synthetic validations of the biosynthetic network of post-iboga natural products are under way and will be the subjects of forthcoming reports.…”

Section: Resultsmentioning

confidence: 99%

Biosynthetically Inspired Transformation of Iboga to Monomeric Post-iboga Alkaloids

Seong

Lim

Han

2019

Chem

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Section: Resultsmentioning

confidence: 99%

Biosynthetically Inspired Transformation of Iboga to Monomeric Post-iboga Alkaloids

Seong

Lim

Han

2019

Chem

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“…Thus, it seems that the first equivalent of lead tetraacetate oxidizes the most susceptible C-3 position in the iboga skeleton to a carbinolamine and the excess of reagent subsequently attacks the indole nucleus but does not continue at C-3 to give the lactam. Previous studies about the lead tretraacetate oxidation in yohimbinoid alkaloids 16 suggests that the O-C(7) bond in 1 would be formed through an intramolecular nucleophilic sub- Despite the fact that the absolute configuration of iboga alkaloids is known, 17 the absolute stereochemistry at C-7 in the corresponding hydroxyindolenines is still undetermined. On the basis of mechanistic considerations, Wenkert et al proposed a 7S absolute configuration for voacangine hydroxyindolenine.…”

Section: Resultsmentioning

confidence: 99%

Obovamine, a New Indole Alkaloid fromStemmadenia obovata

et al. 1996

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The stem bark of the Panamanian plant Stemmademia obovata has afforded a new ibogainetype alkaloid, obovamine (1), whose structure was determined by a combination of spectral interpretation and chemical correlations. Ten known alkaloids, coronaridine, coronaridine hydroxyindolenine, voacangine, voacangine hydroxyindolenine, (19S)-heyneanine, (19S)-heyneanine hydroxyindolenine, (19S)-voacristine, (19S)-voacristine hydroxyindolenine, ajmalicine, and ajmalicinine, were also isolated. Voacangine was the main alkaloid constituent.In a previous work, we reported the isolation of obovatine, bis[11-hydroxycoronaridin-12-yl]-11-hydroxycoronaridine, and voacristine from the leaves 1 and N 1 -methyl-11-hydroxymacusine A from the stem bark 2 of Stemmadenia obovata. Here we report the study of the organic-soluble stem bark fraction. The acidic and neutral crude alkaloidal fractions of the EtOH extract afforded the new iboga indolenine alkaloid obovamine (1) and the known alkaloids voacangine 3 (2), voacangine hydroxyindolenine 4 (3), coronaridine, 5 coronaridine hydroxyindolenine 6 (4), (19S)-heyneanine, 7 (19S)-heyneanine hydroxyindolenine, 8 (19S)-voacristine, 7 (19S)-voacristine hydroxyindolenine, 9 ajmalicine 10 (5), and an epimeric mixture of ajmalicinine 11 (6) and 17-epi-ajmalicinine (7). The known compounds were identified by comparison of their spectral data with those reported in the literature. Results and DiscussionObovamine (1), a minor alkaloid, was isolated as an amorphous compound by a combination of adsorption column chromatography and preparative TLC. The UV maxima at 224 and 286 shown by 1 are similar to those of a 10-methoxy-7-hydroxyindolenine chromophore. 4 The IR spectrum showed an absorption band belonging to a carbonyl ester (1731 cm -1 ) and strong bands (1155, 1090 cm -1 ) attributable to an ether functionalization. The mass spectrum displayed a molecular ion at m/z 382, two amu less than for voacangine hydroxyindolenine (3), and the fragments at m/z 367, [M -15] + 353, [M -29] + , and 323 [M -59] + corresponding to the loss of an ethyl side chain and a carbomethoxy group, respectively.

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“…In order to establish the absolute configuration of compound 5 ( 5a or 5b ), two further experiments were carried out. First, 5 could be correlated with (−)-heyneanine ( 12 ) of known absolute configuration, via oxidation of 12 with Dess-Martin periodinane. The resultant compound 5 had [α] 25 D +23 ( c 0.2, CHCl 3 ) {versus [α] 25 D +21 ( c 0.5, CHCl 3 ) for natural 5 } and NMR data virtually identical to those of the natural product.…”

Section: Resultsmentioning

confidence: 99%

“…Compound 1 (conodusine A) was isolated by fractional crystallization from CH 2 Cl 2 −MeOH solutions containing mixtures of the two C-20 epimers 1 and 2 (with 1 as the major component) as colorless prisms with mp 196−199 °C and [α] 25 D +83 (c 1, CHCl 3 ). The UV spectrum showed absorption maxima at 227, 284, and 294 nm, characteristic of an indole chromophore, while the IR spectrum showed bands due to NH (3396 cm −1 ) and ketocarbonyl (1704 cm −1 ) functions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…In any case, the structure was also confirmed by an X-ray analysis (Figure 2), and the electronic circular dichroism (ECD) data (Figure 3) established the (14S, 16R, 20S, 21R) absolute configuration. Compound 2 (conodusine B, the C-20 α-acetyl epimer of 1) coeluted with 1 during column chromatography, but could be eventually purified by preparative radial chromatography after most of the epimer 1 has been removed by fractional crystallization, as a light yellowish oil, with [α] 25 D −101 (c 0.3, CHCl 3 ). The DART-TOF-MS data showed an [M + H] + ion at m/z 295 (HRMS m/z 295.1815), which analyzed for C 19 H 22 N 2 O, indicating that it is isomeric with 1.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Ibogan, Aspidosperman, Vincamine, and Bisindole Alkaloids from a Malayan Tabernaemontana corymbosa: Iboga Alkaloids with C-20α Substitution

et al. 2016

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Ten new indole alkaloids (1-10) comprising five ibogan, two aspidosperman, one vincamine, and two bisindole alkaloids, in addition to 32 known alkaloids, were isolated from the stem-bark extract of a Malayan Tabernaemontana corymbosa. The structures of these alkaloids were determined based on analysis of the NMR and MS data and, in five instances (1, 3, 5, 6, 8), confirmed by X-ray diffraction analysis. Two of the iboga alkaloids, conodusines B (2) and C (3), and the iboga-containing bisindole tabernamidine B (10) are notable for the presence of an α-substituted acetyl group at C-20 of the iboga carbon skeleton. The iboga alkaloid (+)-conodusine E (5) had MS and NMR data that were identical to those of (-)-ervatamine I, recently isolated from Ervatamia hainanensis. Establishment of the absolute configuration of (+)-conodusine E (5) was based on analysis of the ECD data, correlation with (-)-heyneanine, and X-ray analysis, which showed that (+)-5 belongs to the same enantiomeric series as exemplified by (-)-coronaridine. The configuration at C-20' of the previously reported Tabernaemontana bisindole alkaloid 19'-oxotabernamine (renamed tabernamidine B) required revision based on the present results. Several of the bisindoles showed pronounced in vitro growth inhibitory activity against drug-sensitive and vincristine-resistant KB cells.

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Absolute configuration of the iboga and voacanga alkaloids : chiroptical approach

Cited by 22 publications

References 10 publications

Biosynthetically Inspired Transformation of Iboga to Monomeric Post-iboga Alkaloids

Biosynthetically Inspired Transformation of Iboga to Monomeric Post-iboga Alkaloids

Obovamine, a New Indole Alkaloid fromStemmadenia obovata

Ibogan, Aspidosperman, Vincamine, and Bisindole Alkaloids from a Malayan Tabernaemontana corymbosa: Iboga Alkaloids with C-20α Substitution

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