The Absolute Configuration at C(7) of Voacangine Hydroxyindolenine

✍ Scribed by Alberto Madinaveitia; Gabriel de la Fuente; Antonio González

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: German
• Weight: 143 KB
• Volume: 81
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/(sici)1522-2675(19980909)81:9<1645::aid-hlca1645>3.0.co;2-p

✦ Synopsis

The NMR spectral analysis of voacangine hydroxyindolenine (2) and of some synthetic derivatives, together with mechanistic considerations, permitted to establish its absolute configuration at C(7) as ( R ). The configuration at C(7) in hydroxyindolenines of the ibogamine series is also discussed and would be ( S ).

Compounds 3 and 4 show UV maxima at 293 and 284, respectively, and give a yellow colour with FeCl 3 / HClO 4 spray reagent [2] [6]. The MS of 4 is very similar to that of 3, with peaks at m/z 384 (8), 383 (4), 368 (100, [ M À OAc] ) and 367 (78); the absence of the molecular ion suggests the loss of the acetoxy group at C(7) of these acetoxyindolenines. The peaks at m/z 337 (8) and 353 (20) are due to the loss of an ethyl side chain, and those at m/z 136 (47) and 122 ( ) are characteristic of iboga alkaloids . The 1 H-NMR spectrum of 4 ( Table ) displays signals for a tertiary acetate, a methoxycarbonyl and an aromatic methoxy group, an ethyl side chain, and the absence of the NH signal. The remaining peaks of the spectra were assigned by direct comparison with those of compounds 2 and 3, and confirmed by selective decoupling and 1 H-COSY experiments.