Alkaloids Derived from Ornithine

Content
Introduction
Derived from Ornithine
  - Pyrrolidine & Tropane
  - Pyrrolizidine
Derived from Lysine
  - Piperidine
  - Quinolizidine
  - Indolizidine
Derived from Nicotinic Acid
  - Pyridine
Derived from Tyrosine
  - PEA & Simple TIQ
  - Modified BTIQ
  - Phenethylisoquinoline
  - Terpenoid TIQ
  - Amaryllidaceae
Derived from Tryptophan
  - Simple Indole
  - Simple β-Carboline
  - Terpenoid Indole
  - Quinoline
  - Pyrroloindole
  - Ergot
Derived from Anthranilic Acid
  - Quinazoline
  - Quinoline & Acridine
Derived from Histidine
  - Imidazole
Derived by Amination Reactions
  - Acetate-derived
  - Phenylalanine-derived
  - Terpenoid
  - Steroidal
Purine Alkaloids
  - Saxitoxin & Tetrodotoxin


L-Ornithine (Figure 1) is a non-protein amino acid forming part of the urea cycle in animals, where it is produced from L-arginine in a reaction catalysed by the enzyme arginase. In plants it is formed mainly from L-glutamate (Figure 2). Ornithine contains both δ- and α-amino groups, and it is the nitrogen from the former group which is incorporated into alkaloid structures along with the carbon chain, except for the carboxyl group.

In plants L-Ornithine is formed mainly from L-glutamate
Figure 1

Thus ornithine supplies a C4N building block to the alkaloid, principally as a pyrrolidine ring system, but also as part of the tropane alkaloids (Figure 1). Most of the other amino acid alkaloid precursors typically supply nitrogen from their solitary α-amino group. However, the reactions of ornithine are almost exactly paralleled by those of L-lysine, which incorporates a C5N unit containing its ε-amino group (see Alkaloids Derived from Lysine).