The indole system can be considered to consist of a pyrrole ring and a benzene ring fused together to form two isomeric benzopyrroles, INDOLE and ISOINDOLE.

The indole itself appears to be an essential constituent of the perfumes of flowers such as jasminium and of the citrus species. With respect to their structural features, the indole alkaloids can be divided into two main classes:

The main divisions of the indole alkaloids can be found in:

The indole alkaloids derived from tryptamine and secologanin can be classified into eight types, according to the structural characteristics of their skeletons.

1. Corynanthean or C-type (sarpagine, yohimbine, ajmalicine)

2. Vincosan or D-type (vincoside)

3. Vallesiachotamon or V-type (vallesiachotamine)

4. Strychnan or S-type (vomicine)

5. Aspidospermatan or A-type (condylocarpine)

6. Eburnan or E-type (vincamine)

7. Plumeran or P-type (kopsine)

8. Ibogan or J-type (voaluteine)

More than a thousand alkaloids are derived by combining a tryptamine, tryptophan or dopamine moiety with a nine or ten carbon unit in various forms. The most common being the:

as in the hetero-yohimbine ajmalicine.

or emetine

The C9 / C10 unit was found to be monoterpenoid in origin - the iridoid glucoside SECOLOGANIN.

RAUWOLFIA ALKALOIDS

For centuries the natives of the Himalayan foothills have used the root of Rauwolfia for healing afflictions ranging from snake bites to insanity. Reserpine is the most important constituent.

Reserpine depletes adrenergic vesicles of their transimitters, thereby, reducing amount of neurotransmitter released (NA). This causes hypotension, bradycardia, increased gastrointestinal motolity and increased rate of defecation. It also has a tranquillization effect but has been superseded by the Benzodiazepams.

The original source was from Rauwolfia serpentina from India. Major source at present is Rauwolfia vomitoria from West Africa.
The basic ring system of nearly all Rauwolfia alkaloids are represented in the following four compounds.

  1. Yohimbine, an alpha2 adrenergic blocking agent and a serotonin antagonist.
  2. Ajmalicine
  3. Ajmaline
  4. Sarpagine

Rauwolfia alkaloids

VINCA ROSEA (Catharanthus) [Madagascar Periwinkle).

The widespread reference in folklore of the oral hypoglycemic properties of leaf extracts from the Catharanthus roseus prompted investigations which led to the discovery of DIMERIC INDOLE - dihydroindole alkaloids; VINBLASTINE and VINCRISTINE. These alkaloids produced severe leukopenia in rats suggesting an anti-cancer potential especially for the treatment of leukemia.

These alkaloids are a dimer of CATHARANTHINE and VINDOLINE.

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Georges-Louis Friedli,MSc,PhD
georges-louis@friedli.com