Page 81 - Phytochemistry 2 (06-PG 605)

The polypeptide alkaloids
These polypeptide alkaloids, together with the simple
lysergic amide, ergometrine, represent the most important
medicinally utilized ergot alkaloids. The polypeptide alkaloids are
more complex, high molecular weight, water-insoluble alkaloids.
Though they are also amides of lysergic acid, they are built up
from a lysergic acid moiety forming an amide with a complex
polycyclic polypeptide moiety. The latter moiety is formed up of
three different amino acids.

(a) R1 HO

O (b)
N
CO NH

H N O
O
NCH3

R2 (c)

NH

General structure of the polypeptide alkaloids
(Showing the three amino acids part structures a, b and c)
(Linked together and to the lysergic moiety by three amide

linkages)
Amino acid (a) = α-hydroxyalanine or α-hydroxyvaline
Amino acid (b) = Proline
Amino acid (c) = Valine or Leucine or Phenylalanine
General Characters

Ergot alkaloids are N-monosubstituted amide derivatives of
both lysergic acid and its isomer isolysergic acid that differ only in
configuration at C-8. On treatment with ammonia lysergic and

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