Cylindrospermopsin
![](/Images/godic/202501/07/Cylindrospermopsin_structure20330.png")
![Figure 1. Initial incorrect proposed structure of cylindrospermopsin (CYN), with its four rings labelled (A-D). The incorrect feature was the orientation of the hydroxyl group. This epimer was later identified as 7-epicyclindrospermopsin.](/Images/godic/202501/07/7-epiCYN0330.png")
![Figure 2. Proposed tautomerism between the keto and enol forms, showing the hydrogen bond between the uracil nitrogen and the guanidino hydrogen.](/Images/godic/202501/07/Cylindrospermopsin_tautomers0330.png")
![Figure 3. Deoxycylindrospermopsin, a non-toxic metabolite of C. raciborskii](/Images/godic/202501/07/Deoxycylindrospermopsin0330.png")
Cylindrospermopsin (abbreviated to CYN, or CYL) is a cyanotoxin produced by a variety of freshwater cyanobacteria. CYN is a polycyclic uracil derivative containing guanidino and sulfate groups. It is also zwitterionic, making it highly water soluble. CYN is toxic to liver and kidney tissue and is thought to inhibit protein synthesis and to covalently modify DNA and/or RNA. It is not known whether cylindrospermopsin is a carcinogen, but it appears to have no tumour initiating activity in mice.