Pyrrolizidine alkaloids (PAs) are a group of secondary plant metabolites, with more than 660 known compounds to date. It is widely accepted that PAs are produced by certain plants to protect themselves from herbivorous insects. Chemotaxonomic estimates suggest that PAs are present in more than 6000 plant species, accounting for 3% of all flowering plants worldwide. All PAs share a common pyrrolizidine-like core structure (1-azabicyclo[3.3.0]octane), typically featuring a hydroxymethyl group at C1 and a hydroxyl group at C7, collectively referred to as the necine base (Figure 1). This base is usually esterifed to one or more polyhydroxylated carboxylic acids, known as necic acids, which allow PAs to be classifed as monoesters, open-chained diesters or cyclic diesters. Nearly all PAs can exist in two forms: as tertiary amine PAs and as their more hydrophilic counterparts, PA N-oxides. It is estimated that PA N-oxides are the preferred storage form in the vacuolated tissues of PA-producing plants, while the more lipophilic tertiary amine PAs tend to accumulate in their seeds (Toppel et al. 1988).