Quinazoline Alkaloids

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


Peganine (Figure 107) is a quinazoline alkaloid found in Peganum harmala (Zygophyllaceae), where it co-occurs with the β-carboline alkaloid harmine. It is also responsible for the bronchodilator activity of Justicia adhatoda(Adhatoda vasica) (Acanthaceae), a plant used in the treatment of respiratory ailments. As a result, the alternative name vasicine is also sometimes used for peganine. Studies in Peganum harmalahave clearly demonstrated peganine to be derived from anthranilic acid, the remaining part of the structure being a pyrrolidine ring supplied by ornithine (compare Figure 1, page 292). The peganine skeleton is readily rationalized as a result of nucleophilic attack from the anthranilate nitrogen on to the pyrrolinium cation, followed by amide formation (Figure 107). Remarkably, this pathway is not operative in Justicia adhatoda, and a much less predictable sequence from Nacetylanthranilic acid and aspartic acid is observed (Figure 107).


Figure 107