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 beta-amino acid 3-amino-2,5,7-trihydroxy-8-phenyloctanoic acid (Atpoa). Compounds 1 and 2 have cytotoxic activity towards cancer cell lines in a monolayer assay with mean IC50 values of 0.9 and 3.3 mu g mL(-1), respectively. Compound 2 was shown to be active against tumor cell suspensions derived from solid tumor xenografts in a clonogenic assay (mean IC50 2.4 mu gmL(-1)). Additionally, antiprotozoal activity was observed (Trypanosoma b. rhodesiense, IC50 0.1 mu gmL(-1)) for compound 1. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).