Curacin D is a novel brine shrimp toxic metabolite isolated from a Virgin Islands collection of the marine cyanobacterium Lyngbya majuscula. Structure elucidation of curacin D was accomplished through multidimensional NMR, GC/MS, and comparisons with curacin A. Curacin D provides new insights into structure-activity relationships iii this natural product class as well as some aspects of the likely biosynthetic pathway of the curacins. (C) 1998 Elsevier Science Ltd. All rights reserved.