Pravadoline
Pravadoline (WIN 48,098) is an antinflammatory and analgesic drug with an IC of 4.9 μM and a "K" of 2511 nM at CB, related in structure to nonsteroidal anti-inflammatory drugs (NSAIDs) such as indometacin. It was developed in the 1980s as a new antiinflammatory and prostaglandin synthesis inhibitor, acting through inhibition of the enzyme cyclooxygenase (COX). However, pravadoline was found to exhibit unexpectedly strong analgesic effects, which appeared at doses ten times smaller than the effective anti-inflammatory dose and so could not be explained by its action as a COX inhibitor. These effects were not blocked by  opioid antagonists such as naloxone, and it was eventually discovered that pravadoline represented the first compound from a novel class of cannabinoid agonists, the aminoalkylindoles. Pravadoline was never developed for use as an analgesic, partly due to toxicity concerns (although these were later shown to be a result of the salt form that the drug had been prepared in rather than from the pravadoline itself), however the discovery of cannabinoid activity in this structurally novel family of drugs led to the discovery of several new cannabinoid agonists, including the drug WIN 55,212-2, which is now widely used in scientific  research. Animal studies. Administration of pravadoline on rats showed: The antinociceptive activity of pravadoline cannot be explained by an opioid mechanism, because pravadoline-induced antinociception was not antagonized by naloxone (1 mg/kg, s.c.) and pravadoline did not bind to the opioid receptors at concentrations up to 10 μM.