The Alkaloids of Tabernanthe iboga. Part IV.<sup>1</sup> The Structures of Ibogamine, Ibogaine, Tabernanthine and Voacangine

Bartlett, M. F.; Dickel, D. F.; Taylor, W. I.

doi:10.1021/ja01534a036

Cited by 134 publications

(48 citation statements)

References 6 publications

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“…conjugated nature of the iininium ion, and (ii) the coiljugation of the newly generated double bond between C-17 and C-18 with both the ester and anilino functions. After acid hydrolysis of the ester, decarboxylation inay occur via X in a manner analogous to the mechanism proposed for the Iboga alkaloids (7,12). This ring-opened interinediate renders the molecule more flexible and the decarboxylated interinediate X I is obtained, whereas, as already mentioned above, the cyclic intermediate VIII necessary for decarboxylation of the rigid catharanthine molecule is highly strained.…”

Section: In a Reluted Inuestigatio?t To Be Reported Later We Have Smentioning

confidence: 67%

“…Consideration of the accepted decarboxylation inechanisins (7,12) for these coinpounds leads to the realization that in the case of catharanthine an intermediate of type VIII becomes necessary. Molecular models reveal that this interinediate would be very highly strained and there is serious doubt whether it can exist a t all.…”

Section: In a Reluted Inuestigatio?t To Be Reported Later We Have Smentioning

confidence: 99%

“…So~lle earlier work by tlle Lilly group (8) established that, although dihydrocatharanthine, lilte its relatives in tlle Iboga series (7,11,12), decarboxylated readily to yield the corresponding descarbomethoxy base, epi-ibogainine (VII), catharanthine did not undergo an analogous transformation under these conditions. Although this may seem somewhat puzzling,…”

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confidence: 99%

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Some Aspects of the Chemistry of Catharanthine and Cleavamine

Kutney¹,

Brown²,

Piers³

1965

Can. J. Chem.

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Chemical and spectroscopic evidence is presented for an interesting acid-catalyzed rearrangement of the alkaloid catharanthine. Four reaction products (descarbomethoxycatharanthine and cleavamine and its two dihydro derivatives) were isolated, and their formation is rationalized by a mechanism involving ring-opened intermediates. Evidence is presented in support of the proposed mechanism and, in particular, a novel transannular cyclization leading to the Iboga alkaloid skeleton is shown in support of the steps postulated for the formation of descarbomethoxycathara~~thil~e.The X-ray analysis of cleavamine methiodide established the absolute configuration of the lone asymmetric center present in the molecule and, from these results, the absolute configuration of the Iboga alkaloids can be derived.During investigations by the Lilly group (I) on the di~neric Vinca alkaloids (vincaleultoblastine (VLB), leurosine, and leurocristine), it was found that each was cleaved by concentrated hydrochloric acid to an indole compound and vindoline derivative. The vindoline derivative of VLB and leurosine was desacetylvindoline (I), whereas leurocristine gave des-N(,,-methyl-desacetylvindoline (11). Both VLB and leurocristine afforded the same indole derivative, velbanamine, C19H26N20, but the corresponding compound with leurosine was called cleavainine, C191-12,Nz.In the saine comn~unication it was also reported that the ltnown alkaloid catharanthine (111 (2)), when subjected to the saine acid treatment, also provided cleavamine as one of the reaction products. The suggestion that cleavainine possessed a tetracyclic structure si~nilar to the ltnown Aspidosperma alkaloid quebrachainine (3) stimulated further research in our laboratory to establish conclusively the structure and stereochemistry of this substance. At the outset we felt that this investigation might not only provide indirect evidence for the presence of a catharanthine-like unit in the biologically iinportant VLB molecule, but also illustrate a novel acid-catalyzed rearrangement in the Iboga alltaloid series. Furthermore, if the absolute configuration of the asymmetric center in the molecule could be established, it would provide indisputable evidence for the absolute configuration of the Iboga alltaloids.With this view in mind, we initiated a detailed study of the catharanthine-cleavamine transforination and some of our results concerning the structure of cleavamine have already been published (4). Fortunately, the X-ray analysis of cleavainine methiodide established the structure and absolute configuration a t C-2l as depicted in IV. We now wish to discuss these results in soine detail and to present more recent evidence which is relevant to the mechanism of this interesting transformation.Before considering mechanism, we wish to discuss briefly the stereochemistry of the Iboga alltaloids, since, in conjunction with the results of other workers and the evidence presented herein, it is possible to assign the absolute configuration for this series of

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Section: In a Reluted Inuestigatio?t To Be Reported Later We Have Smentioning

confidence: 67%

Section: In a Reluted Inuestigatio?t To Be Reported Later We Have Smentioning

confidence: 99%

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Some Aspects of the Chemistry of Catharanthine and Cleavamine

Kutney¹,

Brown²,

Piers³

1965

Can. J. Chem.

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“…Fortunately, Dr. William I. Taylor (CIBA, Summit, NJ) had such a pair at hand: Ibogaine (4) and ibogamine (5), the structures of which he had determined shortly before by conventional means [7]. The mass spectra of these two alkaloids (Figure 1) indeed showed an identical pattern (with a shift of 30 u, CH 3 O vesus H), which is, however, very different from that exhibited by 2 and 3.…”

Section: Alkaloidsmentioning

confidence: 99%

Four decades of structure determination by mass spectrometry: From alkaloids to heparin

Biemann

2002

J. Am. Soc. Mass Spectrom.

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The early (1950's and 1960's) use of mass spectrometry in natural products chemistry and its evolution to the present significance in biochemistry is recounted. This methodology allowed the facile and speedy determination of the structure of a number of indole alkaloids, such as sarpagine, quebrachamine, and two groups isolated from the roots of Aspidosperma quebracho blanco. At the same time, the first strategy for the sequencing of small peptides by mass spectrometry was demonstrated. It slowly advanced, over a period of two decades, to an important alternative of the ubiquitous automated Edman degradation. Further advances in methodology and instrumentation established mass spectrometry as today's indispensable tool for the characterization of proteins in biochemistry and biology. A new concept of the ionization of highly acidic compounds as the protonated complexes with basic peptides, which allows the accurate determination of the molecular weights of the former, a highly sensitive method for the sequencing of heparin fragments and related sulfated glycosaminoglycans was developed more recently. (J Am Soc Mass Spectrom 2002, 13, 1254-1272

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“…Most oxidizing agents act as electrophiles and initially attack the C-3 position of the indole ring, leading to the formation of 2-acyl-2 -6) or 3-acylindoles, 7,8) and to the oxidative cleavage of the C-2, C-3 double bond.9,10) We discovered that iodine pentoxide (I2O5), which had not been utilized in organic syntheses, oxidized the nine-membered amide (la) to provide 2-acylindole (2a) in good yield. This reaction was successfully applied to the total synthesis of "strychnos" type indole alkaloids .11)…”

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confidence: 99%

Oxidation of cycloalkan[b]indoles with iodine pentoxide(I2O5).

Yoshida

Goto

Ban

1987

CHEMICAL & PHARMACEUTICAL BULLETIN

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The Alkaloids of Tabernanthe iboga. Part IV.¹ The Structures of Ibogamine, Ibogaine, Tabernanthine and Voacangine

Cited by 134 publications

References 6 publications

Some Aspects of the Chemistry of Catharanthine and Cleavamine

Some Aspects of the Chemistry of Catharanthine and Cleavamine

Four decades of structure determination by mass spectrometry: From alkaloids to heparin

Oxidation of cycloalkan[b]indoles with iodine pentoxide(I2O5).

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The Alkaloids of Tabernanthe iboga. Part IV.1 The Structures of Ibogamine, Ibogaine, Tabernanthine and Voacangine

Cited by 134 publications

References 6 publications

Some Aspects of the Chemistry of Catharanthine and Cleavamine

Some Aspects of the Chemistry of Catharanthine and Cleavamine

Four decades of structure determination by mass spectrometry: From alkaloids to heparin

Oxidation of cycloalkan[b]indoles with iodine pentoxide(I2O5).

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Product

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The Alkaloids of Tabernanthe iboga. Part IV.¹ The Structures of Ibogamine, Ibogaine, Tabernanthine and Voacangine