Further evidence on the intramolecular lactonization in rat liver microsomal metabolism of 12-O-acetylated retronecine-type pyrrolizidine alkaloids.

We have previously found evidence of intramolecular lactonization in rat liver microsomal metabolism of isoline, a 12-O-acetylated pyrrolizidine alkaloid. In this study, the metabolism of another 12-O-acetylated pyrrolizidine alkaloid, acetylduciformine, by the proposed transformation pathway was investigated under the same incubation conditions. Two deacetylated metabolites from acetylduciformine were isolated and purified by chromatographic methods, and further characterized based on their physical properties and spectral data. One metabolite (lankongensisine A) was the lactone of another one (duciformine). Both compounds were first obtained as hydrolyzed metabolites from acetylduciformine by rat liver microsomes. More importantly, the present study provided further evidence for the intramolecular lactonization in the microsomal metabolism of 12-O-acetylated retronecine-type PAs.