Structure, biosynthesis, and biological activities of cyclooligomer depsipeptides from fungi

Cyclooligomer depsipeptides (CODs) are peptolides, in which their symmetric structure ring structure has two or more ester bonds formed and alternately arranged between amino and α-hydroxy acid. CODs belong to four main groups of cyclotetrapeptides, cyclohexadepsipeptides, cyclooctadepsipeptides and diketomorpholines. These compounds have been mainly isolated from Acremonium, Aspergillus, Beauveria, Cordyceps, Fusarium, Isaria, Nigrospora, Peacilomyces, and Verticillium. The biosynthesis of CODs takes place outside the ribosome by giant multi-domain enzymes called nonribosomal peptide synthetases (NRPSs). Two different models about the formation of these depsipeptides were proposed. Fungal CODs are known to exhibit various biological activities, especially insecticidal, antitumoral, antimicrobial and antiviral activities. Therefore, CODs are considered to be natural substances with extremely potential applications in medicine and agriculture. This review highlights the structures, classification, biosynthesis, and biological activities of the fungal CODs.