Tabersonine-p-epoxide

Tabernaemontana divaricata (double flower variety) provided an unusual minor alkaloid, voaharine (178), whose structure was established by X-ray analysis [137]. Voaharine is exceptional in being in all probability a tryptamine and jccologanine derived alkaloid but possessing a 3-quinolone instead of an indole chromophore. Voaharine is probably derived from voaphylline (180) (which is also present in the plant) via oxidation and rearrangement and represents the first instance of a 3-quinolone-type alkaloid obtained from Tabernaemontana. Besides these, and the known alkaloids N-methylvoaphylline (181), pachysiphine (tabersonine-P-epoxide) and apparicine, as well as two new bisindoles (vide infra), the plant also provided several new alkaloids of the aspidosperma-type including (-)-mehranine (179), voafinine (182), N-methylvoafinine (183), voafinidine (184) and voalenine (185) which were obtained in minute amounts [138-140]. 

Conofoline has also been isolated from another Malaysian Tabemaemontana species (Ervatamia peduncularis) under the name pedunculine [185]. The same plant also furnished another dimeric alkaloid, peduncularidine (307), which shares the common oxygenated tabersonine-P-epoxide moiety of conofoline but differs in the second unit which is now an opened form of (-)-mehranine, with a trans diol functionality at position 14 and 15 instead of a P-epoxide function. The epoxide ring opening by a water molecule is anticipated to occur preferentially at the less hindered carbon (14 ) resulting in a H(14 P), H(15 a) configuration. This proposal was supported by the ROESY spectrum which showed correlations between the axial H(2 ) and H( 17 ) with H(14 ), indicating that the latter has p stereochemistry. 

Rodriguez, S. et al. (2003) Jasmonate-induced epoxidation of tabersonine by a cytochrome P-450 in hairy root cultures of Catharanthus roseus. Phytochemistry 64, 401-409... 

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