Ibogan alkaloids

A greater number of compounds has been found among plumeran, cory-nanthean and ibogan alkaloids. The last type seems to be characteristic of all Tabemaemontana plants, being contained in almost all species. 

A new amorphous alkaloid has been recently isolated from the Chinese plant T. bufalina (Ervatamia hainanensis) collected on Hainan Island (53). Its mass spectrum showed a molecular ion at m/z 382, corresponding to C23H30N2O3. From the fragmentation pattern, this compound would appear to be a coronaridine derivative in which a C2H50 unit is attached to the aliphatic moiety of the molecule. The structure 111 with (S) configuration at C-3 was determined by a detailed analysis of its H-NMR spectrum (Table IV) in comparison with the data of other ibogan alkaloids. 

Ibogamines, 358 Ibogane alkaloids, 389 Imidazoles, 245, 246 Iminium salts, 292-293 l,6-lmino[10]annulene, 266 Iminoaziridines, 76 Iminophosphoranes, 106 2-lminotetrahydrofuranes, 202 Incensole, 351 Indanones, 327 Indene, 100 Indenes, 262 Indenones, 430 Indoles, 21-22, 135 Indoline, 277, 314 lodination, 359-360 Iodine, 179-181... 

Alkaloids of plumeran, aspidospermatan, corynanthean, and ibogan types are conveniently subdivided into subtypes depending on further variations of the terpenic portion or, in very few cases, of the indole portion of the fundamental skeleton. The subtypes are named according to the most representative member, even if this is not found in Tabemaemontana. 

Only three examples of ibogan-type oxindole alkaloids are known, and two of them, crassanine (156) and tabemoxidine (155), were found in Tabernaemon-tana. Crassanine (C23H30N2O5, MP 191°C, [a]D +21°) was isolated in minute amounts by Cava et al. from T. crassa (79). Its IR spectrum indicated the presence of two carbonyl groupings (1739 and 1709 cm - ), while its UV spectrum was almost superimposable on that of known 10,11-dimethoxyoxindoles such as kisantine (200). In addition to the carbomethoxy methyl at 3.47 ppm and two aromatic methoxyls at 3.83 ppm (6H), the H-NMR spectrum of 156 exhibited two singlets (1H) at 6.50 and 7.01 ppm and the low-field oxindole NH at 9.30 ppm. The latter values are similar to those recorded for kisantine, and on this basis Cava et al. proposed the structure 102 for crassanine. To date, no evidence is available on the configuration at the C-7 spiro center. 

A unique alkaloid possessing a novel type of ibogan skeleton was isolated from the leaves of 7. dichotama (90) and T. eglandulosa (105). The new com-... 

C = corynanthean-type of alkaloid I = ibogan-type of alkaloid S = strychnan-type of alkaloid... 

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