Isolation and structure of the cytotoxic cycloheptapeptide phakellistatin 13.

A new cyclic hepptapeptide phakellistatin 13(1) had been isolated from the sponge phakellia fusca Thiele, collected at Yongxing Island of China. Its structure was elucidated as cyclo-(Pro~1Trp_leu-Thr-Pro~2-Gly-Phe) on the basis of MS, UV, IR, and high-field NMR (600 MHz) analysis. The compound was significantly cytotoxic against the human hepatoma BEL-7404 cell line with an ED^50<10-2 μg/mL