Page 90 - phytochemistry II -pharmD general

Tests for identification

▪ On treatment of yohimbine with concentrated H2SO4 and crystals of K2Cr2O7,
violet streaks are obtained that turns blue then green (c.f. strychnine).

▪ Yohimbine gives with Mandalin's reagent a blue color that turns to green (c.f.
strychnine that gives a violet color which changes to red).

Uses

Yohimbine is mainly used as an aphrodisiac drug.

c. Rauwolfia alkaloids

Occurrence

Rauwolfia roots (Rauwolfia serpentina, family Apocynaceae) contain several
alkaloids, the most important of which is reserpine.

Rauwolfia alkaloids are subclassified as follows:

▪ The weakly basic tertiary colorless alkaloids e.g. reserpine, deserpidine and
recinamine.

▪ The intermediately basic tertiary colorless alkaloids e.g. ajmaline and
rauwolfine.

▪ The strongly basic quaternary yellow alkaloids e.g. serpentine and serpentinine.

N R1 R2
R1 H

NH Reserpine OCH3 Trimethoxybenzoyl
H OCH3 Trimethoxycinnamyl
H OR2 Rescinamine H Trimethoxybenzoyl
Deserpedine

H3COOC OCH3

Reserpine

Properties

Reserpine occurs as fine, white or pale buff or slightly yellow colored
crystals or crystalline powder, m.p.270 ˚C, with decomposition. It is laevorotatory.
Reserpine and related alkaloids are weakly basic ester, tertiary alkaloids and

possess a carboxylic ring "E".

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