Sesquiterpene lactones structural diversity

The class of natural products under focus of this work, the sesquiterpene lactones (STLs) represent one prime example, as a very large group of secondary metabolites of high diversity, with respect to chemical structure as well as biological activity. The first section of this contribution ( Structural Diversity of Sesquiterpene Lactones ) therefore focuses on a general description and discussion of STL structure in terms of chemical and biological diversity. 

Finally it should not remain unmentioned, that several STLs of other structural types have been found which contain a cyclic peroxide structure. The STL database (see Structural diversity of sesquiterpene lactones ) contains 88 entries with peroxide moieties of which 24 contain this structure as part of a ring system. Of these, 21 are not derived from seco-cadinane but belong to the guaianolide and xanthanolide series. It remains to be shown whether these compounds possess anti-protozoal activity in a similar way as the artemisininoids. 

Apart from the diversity presented by their core structures, sesquiterpenes are commonly decorated with lactone moieties and hydroxyls throughout the basic core. Thus, usually isolated biologically active natural sesquiterpenes are highly oxidized, referred in the literature as sesquiterpe-noids. The a,p-unsaturated lactone functionality is a common feature of many cytotoxic sesquiterpenoids accounting as a powerful alkylating side through a Michael-type addition to suitable biomolecules as the cysteine residues on proteins and enzymes. Thus, several biological active sesquiterpenoids have been isolated and used in traditional and modem... 

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