Dictamins A–C, three unprecedented apotirucallane-type trinortriterpenoids from Dictamnus dasycarpus

Dictamins A–C, the first known examples of apotirucallane-type trinortriterpenoids, were isolated from the root bark of Dictamnus dasycarpus. Their structures and relative configurations were elucidated on the basis of extensive NMR and single-crystal X-ray diffraction analyses. Such compounds might be the key C5 side chain intermediates for an alternative degradation process from protolimonoids (C8 side chain) to limonoids (C4 side chain), bridging an oxidative cleavage biogenetic pathway between these two classes of structurally diverse triterpenoids.