Naturally-Occurring Cyclopeptides: Structures and Bioactivity

Cyclic peptides are a special bioactive group of compounds with interesting pharmacological and biochemical properties. Different natural sources are mentioned in this paper, but interest is focused on those cyclopeptides isolated from higher plants and higher fungi. Cyclopeptides occur in higher plant species, which belong to the following families: Annonaceae, Araliaceae, Asteraceae, Caryophyllaceae, Euphorbiaceae, Fabaceae, Labiatae, Linaceae, Olacaceae, Rhamnaceae, Rubiaceae, Rutaceae, Schizandraceae, Solanaceae, and Violaceae. Basidiomycetes is the group of higher fungi, which has shown to be rich in cyclopeptides, e.g., Amanita, Conocybe, Lepiota, Galerina, and Omphalotus species. Usually these compounds are associated to a toxic response in mammals, as well as to cytotoxic, insecticidal, antimalarial, estrogenic, sedative, nematicidal, antimicrobial, immunosuppressive, and enzyme-inhibitory activities. Structures are elucidated by chemical methods and spectroscopic techniques. Configurational and conformational analyses of some bioactive cyclopeptides are discussed. Conformational studies of the natural cyclopeptides and their derivatives are related to the stereochemical requirements for these bioactive compounds.