Inhibition of protein phosphatase 2A by cyclic peptides modelled on the microcystin ring

Several synthetic analogues of microcystin-LR and nodularin at 1 mM inhibited PP2A. The active microcystin analogues were cyclic heptapeptides envisaged to interact with the catalytic subunit of PP1 and PP2A when an Adda-type hydrophobic group was added. The cyclic core was found to have some intrinsic phosphatase inhibitory activity.