Page 78 - phytochemistry II -pharmD general

CO-R HO-C-R R-OC H
H

N CH3 N CH3 N CH3

(L) Enol (D)

Thus, in solutions, the active water soluble alkaloid ergonovine, undergoes
gradual conversion to the inactive ergonovinine, till an equilibrium mixture is
achieved. They are converted to the isomeric lysergic acid members by refluxing
their alcoholic solution with phosphoric or acetic acids.

In badly stored aqueous solutions i.e. when exposed to light, or irradiated
with UV, ergot alkaloids are changed to the non-active lumi-derivatives. These are
non-fluorescent compounds in which the double bond between C-9 and C-10 is
reduced and an OH group is introduced at C-10. The C9-C10 double bond can be
also easily hydrogenated, by catalytic reduction, to give dihydroderivatives.
Dihydro-ergot alkaloids (e.g.dihydroergotamine) are utilized therapeutically for the
treatment of migraine, but they lose their ecbolic or oxytocic properties.

Lysergic acid alkaloids Alcoholic KOH Isolysergic acid alkaloids
H3PO4 or CH3COOH

Active ergot alkaloids Light or UV Inactive Lumi-derivatives

Tests for identification

1. Van-Urk's test: to a solution of the alkaloids add Van Urk's reagent (solution of
p-dimethyl aminobenzaldehyde, PDAB, in 15% H2SO4, containing traces of
FeCl3) a deep blue color is obtained.

2. Keller’s test: to a solution of the alkaloids in acetic acid add drops of FeCl3
followed by careful addition of concentrated H2SO4 on the wall of the test tube
a blue layer is formed between the two phases.

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