Our previous observation of a putative microginin BGC (mic) in M. aeruginosa LEGE 91341 motivated a search for known or new microginins in this strain. AntiSMASH 17 -based annotation of this BGC allowed for predicting the specificity of three out of the four NRPS modules: two would incorporate Pro and one would incorporate Tyr. Manual inspection of LC-HRESIMS data for a methanolic extract of M. aeruginosa LEGE 91341 revealed 12 features corresponding to compounds with isotope patterns characteristic of one or two chlorinations or to their non-halogenated counterparts (Fig. ). The most abundant features were in the m/z 600-800 range ([M+H] + ) which would be consistent with microginin-like metabolites. Overall, these mass features could be considered as making up four groups of analogues, each group containing variants with different degrees of halogenation (absent, one and two chlorine atoms). Searches for the accurate masses (± 5 ppm) of the compounds in NP Atlas and Dictionary of Natural Products 19 returned no hits for cyanobacteria, suggesting that these were novel compounds.