Isolation and structural elucidation of new cyclotetrapeptides, trapoxins A and B, having detransformation activities as antitumor agents.

New cyclotetrapeptides, trapoxins A and B were isolated from the culture broth of Helicoma ambiens RF-1023. These compounds exhibit detransformation activities against v-sis oncogenetransformed NIH3T3 cells (sis/NIH3T3) as antitumor agents. The structures were found to be new cyclotetrapeptides, cyclo[(S)-phenylalanyl-(S)-phenylalanyl-(R)-pipecolinyl-(2S, 9S)-2-amino-8-oxo-9, 10-epoxydecanoyl-] for trapoxin A and cyclo[(S)-phenylalanyl-(S)-phenylalanyl-(R)-prolyl-2-amino-8-oxo-9, 10-epoxydecanoyl-] for trapoxin B, by X-ray analysis, mass spectrometric, NMR and chemical studies.