# Natural product structural chemistry

Cyanobacteria are a rich source of natural products, small metabolites, with interesting biological activities. Mass spectrometry and nuclear magnetic resonance analysis of cyanobacterial bioactive compounds has led us to discover number of microcystin toxin variants and vide variety of bioactive compounds. Cyanobacteria strains from our culture collection are studied for the presence of toxins and other bioactive compounds.

In recent years we have described (1) new potent serine protease inhibiting linear tetrapeptides, spumigins, aeruginosins and pseudoaeruginosins from Nodularia (Fewer et al. 2009, 2013, Liu et al. 2015), pseudospumigins from Brasilian Nostoc (Jokela et al. 2017) and linear tripeptide nostosins from Nostoc (Liu et al. 2014). (2) An antitoxic cyclic heptapeptide nostocyclopeptide M1, cyclic decapeptide nostoweipeptin W1 and nonapeptidic nostopeptolides L1-4 for hepatotoxic microcystins (Jokela et al. 2010, Herfindal et al. 2011, Liu et al. 2015). (3) Novel lytic cyclic lipotetrapeptides anabaenolysins A and B from benthic Anabaena (Jokela et al. 2012). (4) Novel acetylated cyclodextrins from the benthic Anabaena which are synergistically antifungal with anabaenolysins (Shishido et al. 2015 ) (5) New rare microcystin variants from lichen symbiotic Nostoc and Phormidium from Brazil and USA (Shishido et al. 2013, 2015). (6) Novel antifungal cyclic glycolipononapeptide hassallidins from Anabaena (Vestola et al. 2014). (7) A number of ribosomally produced cyanobactins which were structurally so novel that the definition of cyanobactins have to be revised (Leikoski et al. 2010, 2012, 2013). (8) Novel variants of antifungal compounds hassallidins and scytophycins from new cyanobacterial strains (Shishido et al. 2015).

Further screening (e. g. cell assays, enzymes tests) and characterization of novel bioactive compounds from our culture collection as well as new isolates of cyanobacteria are underway. Our recent studies indicate the frequent production of antifungal and antileukemia activities in cyanobacterial extracts which remain to be identified (Liu et al. 2014, Humisto et al. 2015, Shishido et al. 2015). Our cyanobacterial culture collection is an important basic resource used for screening new cyanobacterial compounds with interesting bioactivities. However, we are interested in finding new relevant clinical targets for the bioactive compound screenings and therefore we are happy to welcome new partners and collaborations to work with us. The discovery of new bioactive metabolites by using a combination of mass spectrometry and genome mining is getting a more and more important approach.