DFT Calculations and ROESY NMR Data for the Diastereochemical Characterization of Cytotoxic Tetraterpenoids from the Oleoresin of Abies balsamea

Eight non-carotenoid tetraterpenoids, abibalsamins C-J (3-10), were isolated from the oleoresin of Abies balsamea. Their chemical structures were determined based on analysis of 1D/2D NMR and MS data. The assignment of their relative configurations was accomplished using homonuclear coupling constants in tandem with ROESY data. However, the presence of two stereogenic centers on a flexible side chain complicated the characterization. In silico models and ROESY data were analyzed in order to assign relative configurations of the isolated tetraterpenoids. Abibalsamins B and H-J showed moderate cytotoxicity against human A549 lung carcinoma cells, with IC50 values ranging between 6.7 and 10 μM.