However, a clear trend in the SAR of these compounds can hardly be derived from these studies. 82 Pyrrolizidine- N -oxides have typically lower acute and long-term toxicity than the corresponding tertiary amines and both usually coexist in plants. 4 They are present in 3% of all flowering plants such as Asteraceae , Boraginaceae , and Leguminosae . 84 They play a role in chemical ecology, as pyrrolizidine- N -oxides are reduced by enzymes in the liver and microbes of the gastrointestinal tract of herbivores.
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