Resiniferatoxin (RTX) is a naturally occurring, ultrapotent capsaicin analog that activates the vanilloid receptor in a subpopulation of primary afferent sensory neurons involved in nociception (the transmission of physiological pain). RTX causes a novel ion channel in the plasma membrane of sensory neurons — the transient receptor potential vanilloid 1 — to become permeable to cations, most particularly the calcium cation; this evokes a powerful irritant effect followed by desensitization and analgesia.
Research is being conducted at the National Institutes of Health and the University of Pennsylvania to design a novel class of analgesics from the latex of resin spurge (Euphorbia resinifera), a cactus-like plant commonly found in Morocco that contains high concentrations of RTX.
A total synthesis of (+)-resiniferatoxin was completed by the Wender group at Stanford University in 1997. As of 2007, this represents the only complete total synthesis of any member of the daphnane family of molecules.