Celastrofurans A-G: Dihydro-β-Agarofurans from the Australian Rainforest Vine Celastrus subspicata and Their Inhibitory Effect on Leucine Transport in Prostate Cancer Cells

Seven new dihydro-β-agarofurans, celastrofurans A–G (1–7), along with two known secondary metabolites, 9β-benzoyloxy-1α-furoyloxydihydro-β-agarofuran (8) and (1R,2R,4R,5S,7R,9S,10R)-2-acetoxy-9-benzoyloxy-1-furoyloxydihydro-β-agarofuran (9), were obtained from the leaves of the Australian rainforest vine, Celastrus subspicata. The structures of the new compounds were determined by detailed spectroscopic (1D/2D NMR) and MS data analysis. The absolute configurations of compounds 1–4 were defined by ECD and single-crystal X-ray diffraction studies. All compounds were found to exhibit inhibitory activity on leucine transport in the human prostate cancer cell line LNCaP with IC50 values ranging from 7.0 to 98.9 μM. Dihydro-β-agarofurans 1–9 showed better potency than the L-type amino acid transporter (LAT) family inhibitor, 2-aminobicyclo[2.2.1]-heptane-2-carboxylic acid (BCH).