Pyrroloindole alkaloids

L-tyrosine Tyrosine-derived alkaloids Indole alkaloids Quinoline alkaloids /3-carboline alkaloids Pyrroloindole alkaloids Ergot alkaloids Iboga alkaloids Corynanthe alkaloids Aspidosperma alkaloids Protoalkaloids Terpenoid indole alkaloids True alkaloids... 

The indole nucleus can change during the synthesizing reaction into quinoline nucleus (Figure 32). Moreover L-tryptophan, the precursor, provides both /3-carboline and pyrroloindole nuclei. Iboga, Corynanthe and Aspidosperma nuclei also originate from L-tryptophan (Figure 32). Alkaloids with nuclei derived from this amino acid tend to be very active compounds with a relatively widespread provenance in nature (Table 10). 

Eserine (physostigmine) has a pyrroloindole skeleton. This alkaloid is used as an anticholinesterase drug, which is fairly important in the treatment of Alzheimer s disease. Eserine is synthesized in Physostigma venenosum and stored in the seeds of this leguminous plant. The synthesis pathway starts with tryptamine, which is transformed into eserine (Eigure 45). 

This structural group of indole alkaloids covers simple indole alkaloids (e.g., tryptamine, serotonin, psilocin and psilocybin), /3-carboline alkaloids (e.g., harmine), terpenoid indole (e.g., ajmalicine, catharanthine and tabersonine), quinoline alkaloids (e.g., quinine, quinidine and cinchonidine), pyrroloindole... 

Psychotridine see pyrroloindole alkaloids. Psychotrine see ipecac alkaloids. 

The number of isolated alkaloids of this type has increased markedly in the past years. Besides pentameric pyrroloindoles such as psychotridine and the hexamer vatine, similar structures containing up to 8 tryptamine units have been discovered, e.g., the octamer vatami-dine from a novel Calycodendron species belonging to the tribe Psychotrieae (Rubiaceae). Alkaloid extracts from Psychotria species exhibit appreciable cy-... 

FIGURE 1.8 L-tryptophan, with its aromatic side chain, is a precursor of indole, terpenoid indole, quinoline, pyrroloindole, and ergot alkaloids. 

Scheme 14.15 Kawasaki s syntheses of pyrazino-pyrroloindole alkaloids via domino Wittig-Horner/isomerization/Claisen rearrangement.

---