Pseudotheonamides, Serine Protease Inhibitors from the Marine Sponge Theonella swinhoei1

Six new peptides with serine protease inhibitory activity have been isolated from the marine sponge Theonella swinhoei . Their structures including absolute stereochemistry were unambiguously established by interpretation of spectral data and chemical degradation. Pseudotheonamides A 1 ( 1 ), A 2 ( 2 ), and B 2 ( 3 ) are linear pentapeptides embracing the rare piperazinone and piperidinoiminoimidazolone ring systems. Pseudotheonamide C ( 4 ) contains v-Tyr (vinylogous tyrosine) instead of a piperazinone ring. Pseudotheonamide D ( 5 ) is a tetrapeptide which lacks a C -terminal k-Arg (α-ketohomoarginine) unit. Dihydrocyclotheonamide A ( 6 ) is a reduction product of the known cyclotheonamide A ( 7 ). 2