Isolation of four new cyclic depsipeptides, antanapeptins A-D, and dolastatin 16 from a Madagascan collection of Lyngbya majuscula

Examination of a Lyngbya majuscula collection from Antany Mora, Madagascar, led to the isolation of dolastatin 16 (5), a promising antineoplastic metabolite first reported from the marine mollusc Dolabella auricularia. In addition, a new series of depsipeptides, antanapeptins A-D (1-4), were discovered. Their structures were deduced by 2D NMR and mass spectrometry and are analogous to the molluscan kulomo'opunalides and the recently reported cyanobacterial metabolites, georgamide and the yanucamides. The antanapeptins were evaluated in several biological assays; however, this series did not exhibit activity.