Cytotoxic Withanolides from the Flowers of Datura metel

Chemical investigation of a methanol extract of the flowers of Datura metel has led to the isolation of 10 new withanolides, withametelins I−P (1−8), 1,10-seco-withametelin B (9), and 12β-hydroxy-1,10-seco-withametelin B (10), together with seven known withanolides. The structures of 1−10 were elucidated by means of spectroscopic methods, and the absolute stereochemistry of 1 was confirmed by single-crystal X-ray analysis. Compounds 1, 3, 4, and 6 exhibited cytotoxic activities against A549 (lung), BGC-823 (gastric), and K562 (leukemia) cancer cell lines, with IC50 values ranging from 0.05 to 3.5 μM.