Sonny Larsson

Naturally Occurring Xanthones; Latest Investigations: Isolation, Structure Elucidation and Chemosystematic Significance

In this review, an updated literature survey covering the reports of naturally occurring xanthones in the period of 2005-2008 is presented. In some 143 studies, the isolation of 264 different xanthones from 36 plant species (representing 15 genera in 6 families of higher plants), 7 species of fungi, and 1 lichen species were reported. Of these, 122 compounds were isolated for the first time from nature. We discuss plant origin, the way of separation, and spectral analysis done for structure elucidation, along with a brief discussion of the chemosystematic significance.

Distribution of circular proteins in plants: large-scale mapping of cyclotides in the Violaceae

During the last decade there has been increasing interest in small circular proteins found in plants of the violet family (Violaceae). These so-called cyclotides consist of a circular chain of approximately 30 amino acids, including six cysteines forming three disulfide bonds, arranged in a cyclic cystine knot (CCK) motif. In this study we map the occurrence and distribution of cyclotides throughout the Violaceae. Plant material was obtained from herbarium sheets containing samples up to 200 years of age. Even the oldest specimens contained cyclotides in the preserved leaves, with no degradation products observable, confirming their place as one of the most stable proteins in nature. Over 200 samples covering 17 of the 23–31 genera in Violaceae were analyzed, and cyclotides were positively identified in 150 species. Each species contained a unique set of between one and 25 cyclotides, with many exclusive to individual plant species. We estimate the number of different cyclotides in the Violaceae to be 5000–25,000, and propose that cyclotides are ubiquitous among all Violaceae species. Twelve new cyclotides from six phylogenetically dispersed genera were sequenced. Furthermore, the first glycosylated derivatives of cyclotides were identified and characterized, further increasing the diversity and complexity of this unique protein family.