Phakellistatins 2 and 4 are cyclic peptides with cancer cell growth inhibitory properties isolated from the ocean marine sponges Phakellia carteri and Phakellia costata. To verify the proposed structures of natural phakellistatins 2 and 4, the given sequential structures were synthesized and their NMR spectra compared with the natural product. A completely different spectral pattern indicates that the structure of the natural compound should be different in both cases. The synthetic compounds according to the formula of phakellistatin 2 and 4 turned out to be inactive against several human cancer cell lines.