(Figure Presented) Melotenine A (1), an unprecedented skeleton with a 6/5/5/6/7 pentacyclic rearranged ring system, was isolated from Melodlnus tenuicaudatus. The structure was elucidated by means of spectroscopic methods and further confirmed by the single-crystal X-ray diffraction analysis. Â possible biogenesis was also proposed. Melotenine A exhibited potential Inhibition against five human cancer cell lines. © 2010 American Chemical Society.