Sesquiterpene lactones (STLs) present one of the largest groups of plant specialized metabolites with a wide range of biological activities. They are a valuable source for new plant derived drugs and drug leads since they contain several important chemical properties responsible for their versatile therapeutic potential.
The aim of this study was to analyze and compare the chemical diversity of all types of STLs in different plant groups, both qualitatively and quantitatively. For this purpose, over 5,200 STLs have been compiled and their plant origin has been recorded, resulting in a comprehensive dataset comprising over 8,600 entries. An overview of skeleton classes and their distribution among plant families was given by assigning the STLs to their major classes. An extensive scaffold diversity analysis was performed based on the molecular framework of these compounds using established metrics. Furthermore, molecular diversity and similarity was assessed via 2D fingerprint and clustering analysis.
The results highlighted significant differences in the degree of chemical diversity. It was demonstrated that the investigated plant families have tendencies to produce certain types of skeletons. The quantity and distribution of skeleton classes was determined per plant family and genus, as well as the proportions of skeleton classes to other STL producing families. Analyzing the scaffold diversity showed that they possessed specific sets of molecular frameworks with a considerable variation in their frequency of occurrence. Even if many plant families produce STLs belonging to the same skeleton class, their corresponding molecular frameworks differ. Clustering analysis confirmed the known large structural diversity and revealed similarities and differences of the compounds. The metrics employed enabled to qualitatively divide STLs into smaller groups with similar structural features, which reflected biologically and chemically different STLs and pointed out the differentiation of various plant groups, up to the taxonomic rank of the species.
Taken together, these analyses provided a comprehensive insight into scaffold and molecular diversity of STLs. Due to the detailed taxonomic annotation, the distinct distribution of different types of STLs was captured. This dataset represents the latest detailed compilation of STLs in the angiosperms, which can be used as a basis for further chemoinformatic or chemosystematic analyses. To provide an example of potential implementations, the results were utilized in a phylogenetic exploration of these metabolites.