Six new metabilites, nostopeptin BN920 (1), nostoginin BN741 (2), nostoginin BN578 (3), banyascyclamide A (4) banyascyclamide B (5) and banyascyclamide C (6), were isolated from the hydrophilic extract of a Nostoc sp. The planar structure of compounds 1–6 was determined by homonuclear and inverse-heteronuclear 2D NMR techniques as well as high-resolution mass spectrometry. The absolute configuration of the asymmetric centers was studied using Marfey's method for HPLC. Compound 1 inhibits the serine-protease chymotrypsin while compound 2 inhibits amino-proteases. q 2002 Elsevier Science Ltd. All rights reserved.