Linearized and truncated microcystin analogues as inhibitors of protein phosphatases 1 and 2A.

A series of acyclic, truncated microcystin analogues, comprised of the dienic beta-amino acid (Adda) and up to four additional amino acids characteristic of the parent toxin, was synthesized and screened for activity as inhibitors of PP1 and PP2A. Despite a recent report to the contrary for a microcystin-derived tetrapeptide degradation product, none approaches the potency of microcystin itself.