One-step targeted accumulation and detection of camptothecin analogues from fruits of Camptotheca acuminata Decne using bilayer solid-phase extraction coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry

Camptothecins, a kind of monoterpene-quinoline alkaloids from Camptotheca acuminata Decne, have long attracted much attention worldwide as an anti-cancer drug. However, there is still a lack of effective methods for the accumulation and discovery of camptothecin analogues from botanic resources for camptothecin-based drug research. This work develops a one-step method for the targeted accumulation, quick detection, and identification of camptothecin analogues from C. acuminata fruit using bilayer solid-phase extraction coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry (bilayer-SPE-UHPLC-Q-TOF-MS/MS). The bilayer-SPE cartridge, with polyamide (PA) as the upper layer and octadecyl silane (ODS) as the lower layer, was designed for the removal of flavonoid and ellagic acid impurities and the enrichment of camptothecins for further MS analysis. Subsequently, the mass spectrometry fragmentations, especially multistage retro-Diels-Alder cleavage, were summarized based on the MS/MS data of 10 reference camptothecins. The UHPLC-Q-TOF-MS/MS conditions were optimized, and the MS/MS data of the potential camptothecin analogues in the bilayer-SPE enriched fractions were analyzed. A total of 30 camptothecin analogues, including 15 new compounds, were identified from the fruit according the fragmentation pathways of the reference standards. The proposed structure of peak 20 was confirmed using its NMR data through rapid enrichment and purification. Overall, the bilayer-SPE enrichment and reliable mass spectrometry fragmentation in our work could provide an effective and simple method for the exploration of the biosynthesis pathway and metabolomics of camptothecin analogues.