<unk> s are a group of macrocyclic lactones first discovered in the late 1960s in a species of<unk> zoan, Bugula neritina. Believed to be produced by symbiont bacteria to protect the<unk> zoan larva from predation, they have cytotoxic properties and are under investigation as anti-cancer agents and as a memory enhancement agent.
In vitro trials have shown<unk> s to act synergistically with other anti-cancer drugs and to modulate protein kinase C (PKC) activity, with a potent antileukemic effect and action against lung, prostate and non-Hodgkin's lymphoma tumor cells.
Human clinical trials have been less promising, but suggest<unk> s to have a potentially useful synergistic action with other chemotherapeutic agents.
The low concentration in<unk> zoans (to extract one gram of<unk> , roughly one tonne of the raw<unk> zoans is needed) makes extraction unviable for large scale production. Due to the structural complexity, synthesis has proved difficult, with only a few total syntheses reported so far.  However, structurally simpler synthetic analogs have been prepared which exhibit similar biological profile and in some cases greater potency, which may provide a practical supply for clinical use.
Bryostatin
Pentostatin
Follitropin beta
Histrelin
Menotropins
Somatropin
Growth hormone-releasing hormone
Gonadotropins