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The isolation and structural characterization of three new heterocyclic and macrocyclic peptides, balgacyclamides A-C, from Microcystis aeruginosa EAWAG 251 are reported. The constitutions were determined by 2D-NMR methods and mass spectrometry, and the configurations were assigned after ozonolysis and hydrolysis by HPLC-MS methods using Marfey's method as well as GC-MS using authentic standards. Balgacyclamides A and B were active against Plasmodium falciparum K1 in the low micromolar range, while displaying low toxicity to rat myoblasts.

By using the Telospot assay, 27 different extracts of cyanobacteria were evaluated for telomerase inhibition. All extracts showed varying, but significant activity. We selected Microcystis aeruguinosa PCC 7806 to identify the active compound and a bioassay guided fractionation led us to isolate mixtures of sulfoquinovosyl diacylglycerols (SQDGs), which were identified by 2D NMR and MS/MS experiments. Pure SQDG derivatives were then synthesized. The IC(50) values of pure synthetic sulfoquinovosyl dipalmitoylglycerol and the monopalmitoylated derivative against telomerase were determined to be 17 and 40 μM, respectively. A structure-activity relationship study allowed the identification of compounds with modified lipophilic acyl groups that display improved activity., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)