Annonaceous acetogenins within extracts: dereplication by HPLC-ESI-LTQ-Orbitrap® using post-column lithium infusion

Annonaceous acetogenins (AAGs) are a homogenous class of polyketides proposed as environmental neurotoxins. Previous dereplication studies of AAGs were limited by the use of low resolution mass spectrometers. Only poor information in terms of structures was provided due to the limited fragmentation of protonated or sodiated species. An innovative approach, using reversed-phase high-performance liquid chromatography coupled to a hybrid linear ion trap/orbitrap mass spectrometer (LTQ-Orbitrap®), was therefore performed. Sensitivity was enhanced by post-column infusion of lithium, as AAGs have a high affinity for this cation. High level of structural information was obtained from low-energy-CID fragmentation experiments of lithium-cationized AAGs ([M+Li]⁺ ions). The method was then applied to a total ethyl-acetate extract of soursop nectar (Annona muricata L.), giving surprising insights on the number, structural types and diversity of AAGs within a single extract.