Abstract
Pyrrolizidine alkaloids (PAs) are heterocyclic secondary metabolites with a typical pyrrolizidine motif predominantly produced by plants as defense chemicals against herbivores. They display a wide structural diversity and occur in a vast number of species with novel structures and occurrences continuously being discovered. These alkaloids exhibit strong hepatotoxic, genotoxic, cytotoxic, tumorigenic, and neurotoxic activities, and thereby pose a serious threat to the health of humans since they are known contaminants of foods including grain, milk, honey, and eggs, as well as plant derived pharmaceuticals and food supplements. Livestock and fodder can be affected due to PA-containing plants on pastures and fields. Despite their importance as toxic contaminants of agricultural products, there is limited knowledge about their biosynthesis. While the intermediates were well defined by feeding experiments, only one enzyme involved in PA biosynthesis has been characterized so far, the homospermidine synthase catalyzing the first committed step in PA biosynthesis. This review gives an overview about structural diversity of PAs, biosynthetic pathways of necine base, and necic acid formation and how PA accumulation is regulated. Furthermore, we discuss their role in plant ecology and their modes of toxicity towards humans and animals. Finally, several examples of PA-producing crop plants are discussed.
Highlights
Pyrrolizidine alkaloids (PAs) are heterocyclic organic compounds synthesized by plants that are thought to act as defense compounds against herbivores [1]
While necine bases are synthesized by a common pathway, different necic acids are formed by distinct modes
Degradation studies showed that the necine base had necic acid monocrotalic acid contained most of the base had incorporated incorporatedlittle littleradioactivity radioactivitywhile whilethe the necic acid monocrotalic acid contained most of activity
Summary
Pyrrolizidine alkaloids (PAs) are heterocyclic organic compounds synthesized by plants that are thought to act as defense compounds against herbivores [1]. PAs consist of a necine base esterified with a necic acid. The necine base typically includes pyrrolizidine, a bicyclic aliphatic hydrocarbon consisting of two fused five-membered rings with a nitrogen at the bridgehead [4] (Figure 1). Loline alkaloids may be formally considered as PAs since they possess a pyrrolizidine system, it contains an ether bridge linking carbon 2 (C-2). Contrast to necine bases, the rings the and ringsgranatane of tropanealkaloids and granatane alkaloids are than bridged rather thanseveral fused. Is hydroxylation of the necine base and/or necic acid, and acetylation groups of the itacid not surprising that several hundreds of different. As the necine base of trachelanthamine (Figure 5C) and the nervosines [12] (Figure 5E), Examples for PAs containing and (+)-isoretronecanole are acetyllaburnine [13].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
