A Novel β‐Amino Acid in Cytotoxic Peptides from the Cyanobacterium Tychonema sp.

The cyclic dodecapeptides tychonamide A (1) and B (2) isolated from the methanolic extract of the cyanobacterium Tychonema sp. contain the novel β‐amino acid 3‐amino‐2,5,7‐trihydroxy‐8‐phenyloctanoic acid (Atpoa). Compounds 1 and 2 have cytotoxic activity towards cancer cell linesin a monolayer assay with mean IC50 values of 0.9 and 3.3 μg mL–1, respectively. Compound 2 was shown to be active against tumor cell suspensions derived fromsolid tumor xenografts in a clonogenic assay (mean IC50 2.4 μg mL–1). Additionally, antiprotozoal activity was observed (Trypanosoma b. rhodesiense, IC50 0.1 μg mL–1) for compound 1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)