Banyasin A and banyasides A and B, three novel modified peptides from a water bloom of the cyanobacterium Nostoc sp.

Three new modified peptides banyasin A, banyaside A and banyaside B were isolated from the hydrophilic extract of a natural bloom of the cyanobacterium Nostoc sp. The planar structure of the new compounds was determined by homonuclear and inverse-heteronuclear 2D NMR techniques as well as high-resolution mass spectrometry. Banyasides A and B, are structurally closely related to the cyanobacteria metabolite, suomilide and to the sponge derived, dysinosins. The absolute configuration of the asymmetric centers was studied using Marfeyʹs method for HPLC. Banyaside A and B were found to be trypsin and thrombin inhibitors.