Pyrrolizidine, Quinolizidine, and Indolizidine Alkaloids

Abstract

Pyrrolizidine, quinolizidine, and indolizidine alkaloids are chemically diverse and restricted in distribution. Some similarities in structures and biosynthesis exist, but as the pathways become more clear, these three major groups of alkaloids definitely are of distinct origins. Pyrrolizidine alkaloids are derived from arginine or ornithine and possess two fused 5-membered rings that share a nitrogen atom. Quinolizidine alkaloids are derived from lysine and have two fused 6-membered rings that share a nitrogen atom. Indolizidine rings have a 5-membered ring fused to 6-membered ring and share a nitrogen atom. Pyrrolizidine, quinolizidine, and indolizidine alkaloids are involved in many plant-herbivore interactions, but are of anthropocentric importance chiefly because of their involvement in livestock poisoning, although several have antitumor activity and others are used medicinally. The phenanthroindolizidine alkaloids are a major subgroup of indolizidine alkaloids.