Phytochemical Investigation and Cytotoxic Activity of Annona amazonica (Annonaceae): Comprehensive Spectroscopic Characterization of N-Formylactinodaphnine

Annona amazonica R. E. Fries (Annonaceae) is a tropical species native to Central and South America whose phytochemical profile remains poorly investigated. In the present study, the bark of A. amazonica was subjected to phytochemical investigation using conventional chromatographic techniques, leading to the isolation and identification of 18 metabolites comprising a diterpene, sesquiterpenes, steroids, ketosteroids, and alkaloids. Attention was given to N-formylactinodaphnine (16), which was isolated and comprehensively characterized by high-resolution electrospray ionization mass spectrometry (HRESIMS), infrared spectroscopy (IR), and one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy. The present study provides a complete spectroscopic dataset for this compound and documents its occurrence in A. amazonica. The other isolated metabolites further expand the known phytochemical profile of the species. The effects of the isolated compounds on cellular viability were evaluated against HepG2, HCT116, MDA-MB-231, MCF-7, and U-87 MG human cancer cell lines and MRC-5 fibroblasts using the Alamar Blue assay after 72 h of incubation. Actinodaphnine (14) activity was detected across all five evaluated cancer cell lines, with IC50 values ranging from 5.59 to 11.73 μg/mL. N-Methylactinodaphnine (cassythicine) (15) had an IC50 value of 4.27 μg/mL against HCT116 cells; because of the limited amount of isolated material, compound 15 was evaluated only against HCT116 and MRC-5 cells. Overall, the results expand the phytochemical knowledge of A. amazonica, provide comprehensive spectroscopic documentation of N-formylactinodaphnine (16) from this species, and identify alkaloids with measurable in vitro activity in the cell-based viability assay.