Two novel cyclic peptides with antifungal activity from the cyanobacteriumTolypothrix byssoidea (EAWAG 195)

Two novel cyclic tridecapeptides, tolybyssidins A (1) and B (2), were isola ted from the culture medium of mass cultured cyanobacterium Tolypothrix bys soidea (EAWAG 195) by means of bioguided isolation. The gross structures of these peptides were determined by 1D and 2D NMR experiments and tandem mas s spectrometry. Both peptides contain the nonnatural amino acid dehydrohomo alanine (Dhha) as well as proteinogenic amino acids albeit with D- or L-con figuration. The compounds exhibit moderate antifungal activity against the yeast Candida albicans.