Abstract
A large proportion of the marine natural products actually under clinical investigation are peptide secondary metabolites with unusual amino acids residues. This growing family of compounds can be produced via two major pathways, ribosomal and nonribosomal. In this chapter are presented and illustrated, with a few famous examples, ribosomal- and nonribosomal-derived peptides. Attention is focused on five families of biologically active marine peptides of diverse origin, ranging from the oldest living cell of the world, the cyanobacteria, to more sophisticated organisms such as tunicates or mollusks. The discussed peptides illustrate differently the structural features and diversity found in marine-derived peptides; laxaphycins as an example of true peptides; dolastatins, didemnins and kahalalides are discussed in connection with their clinical trials; and azole/azoline-containing cyanobactins to exemplify the extraordinary chemical diversity within a single organism. Information about their biological properties and mechanisms of action is discussed when available.