Ajmalicine-type alkaloids serpentine

The arbitrary classification of Rauwolfia alkaloids (91) is simplified here, and it is slightly different from a recent arrangement (92). The Rauwolfia alkaloids can all be regarded as yohimbinoid derivatives as shown in Chart I, viz. the yohimbines (all yohimbine isomers) 18-hydroxyyohimbines (reserpine-type alkaloids) ring E heterocycles and their anhydronium analogs (ajmalicine, serpentine) ajmaline-type (which includes sarpagine) and compounds of unknown constitution. 

Ajmalicine, 19-epi-ajmalicine and tetrahydroalstonine are formed from 4,21-dehydrogeissoschizine via cathenamine (Fig. 2.9). The enzymatic synthesis of these corynanthe-type alkaloids has been investigated using C. roseus cell suspension cultures, and the enzymes involved have been reviewed by De Luca (1993) and Ziegler and Facchini (2008). Ajmalicine can be oxidized by POD to serpentine. This reaction may take in the vacuole. 

Several important alkaloids have been isolated from Catharanthus roseus plants ajmalicine (34) and serpentine (35) from the root, and the dimeric alkaloids vinblastine (36) and vincristine (37) from the leaves. Therefore, much research has been done on production of these alkaloids by means of plant cell culture. Catharanthus roseus is, in fact, one of the most widely studied plants for the production of secondary metabolites in cell culture systems. We here discuss the two types of alkaloids separately. Table XXIX summarizes patents concerning the production of alkaloids by means of cell cultures of C. roseus. 

The pharmacological significance of ajmalicine stems from its use in the treatment of hypertension and obstructive circulatory diseases. Serpentine and ajmalicine can easily be transformed into each other by means of, respectively, simple reduction or oxidation. The yearly production of ajmalicine is estimated to be about 3600 kg (2). Ajmalicine and serpentine are the major alkaloids found in cell and tissue cultures of C. roseus. Both are representatives of corynanthean-type indole alkaliods, of which more than 25 different compounds are isolated from C. roseus cultures (592). 

---