Nodularin-R is a cyclic nonribosomal peptide produced by the planktonic cyanobacterium <i>Nodularia spumigena</i>. This cyanobacterium forms blooms in brackish water bodies throughout the world. Nodularin-R is a pentapeptide and contains several unusual non-proteinogenic amino acids such as methyldehydrobutyrine and the _-amino acid ADDA, (all-S,all-E)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid. Nodularin-R is a cyanotoxin and poses a health risk for wild and domestic animals as well as humans. Nodularin-R is a potent hepatotoxin and may cause serious damage to the liver.