American Chemical Society and American Society of Pharmacognosy (May 30, 2018)   Four new microcystin congeners are described including the first three examples of microcystins containing the rare doubly homologated tyrosine residue 2-amino-5-(4-hydroxyphenyl)pentanoic acid (Ahppa) (1–4). Large-scale harvesting and biomass processing allowed the isolation of substantial quantities of these compounds, thus enabling complete structure determination