Terpecurcumins A–I from the Rhizomes of Curcuma longa: Absolute Configuration and Cytotoxic Activity

Terpecurcumins A–I (1–9), together with three known analogues (10–12), were isolated from the rhizomes of Curcuma longa (turmeric). They were derived from the hybridization of curcuminoids and bisabolanes. The structures and absolute configurations of 1–9 were elucidated on the basis of extensive spectroscopic data analysis, including NMR and electronic circular dichroism spectra. The configuration of 10 was further confirmed by X-ray crystallography. A plausible biogenetic relationship for 1–12 is proposed. Compounds 4, 6, 7, 10, and 11 showed higher cytotoxic activities (IC50, 10.3–19.4 μM) than curcumin (IC50, 31.3–49.2 μM) against human cancer cell lines (A549, HepG2, and MDA-MB-231).