Okadaic acid (OA) is a naturally occurring polyether toxin that was originally derived from marine dinoflagellates, Prorocentrium spp.. It is a reversible, potent and selective inhibitor of two serine threonine protein phosphatases: PP2A-C (PP2A) which is inhibited completely at 1 nM and PP1 which is inhibited at higher concentrations (IC50= 10-15 nM). PP2B is much less sensitive to okadaic acid than PP1, while PP2C is not inhibited. This selectivity is the basis for an improved identification and quantification procedure for these enzymes. The hydrophobic backbone of okadaic acid enables it to enter cells where it stimulates intracellular protein phosphorylation. It mimics the effects of insulin, enhances transmitter release at neuromuscular junctions, causes vasodilation and is a very potent tumor promoter. Okadaic acid is an extremely useful tool for studying cellular processes that are regulated by phosphorylation. Okadaic Acid is an activator of PKC.

Orsellinic acid is a common salicylic acid unit in the biosynthesis of secondary metabolites in actinomycetes, fungi, and lichens, formally isolated from Chaetomium cochliodes in 1959. Orsellinic acid is a key biosynthetic intermediate of many depside metabolites in lichen and fungi. Orsellinic acid is also an important polar co-metabolite present in many fungi, notably Trichomonacea, however, its contribution to overall bioactivity is not well understood. Orsellinic acid is a useful standard for bioassay and analytical techniques for dereplication of common cometabolites.