Seven new didemnins-didemnins M (1), N (2), X (3), and Y (4), nordidem
nin N (5), epididemnin A(1) (6), and acyclodidemnin A (7)-were isolate
d from an extract of the Caribbean tunicate Trididemnum solidum. The s
tructures of these compounds were assigned, based on FABMS, high-field
NMR data, and chemical degradation studies. Biological activities of
these peptides are also described.