Abstract: The lipophilic extract of the freshwater blue-green alga Oscillatoria acutissima contains two novel macrolides, acutiphycin (1) and 20, 21-didehydroacutiphycin (2), which exhibit cytotoxicity and antineoplastic activity. The structures and absolute stereochemistries of 1 and 2 have been determined by spectral studies and chemical degradation.
