Recent discoveries in the search for non‐opiate analgetics

A novel phenanthridine, nantradol (1), resulted from a search to dissect out analgetic activity from the cannabinoid molecule. Nantradol possesses two to seven times greater potency than morphine across a battery of analgetic tests. Despite this morphine‐like profile, nantradol does not bind to the opiate receptor. Nantradol has a total of five asymmetric centers and was studied as a 50:50 mixture of two diastereomers, both of which possess thetrans6a, 10a stereochemistry and have β‐oriented substituents at positions 6 and 9. Evidence is provided that, in common with the opiates, the analgetic actions of nantradol are stereospecific, the majority of the activity residing in a single levorotatory isomer. The stereospecificity and potency of the analetic effects of the nantradol series suggests a highly specific interaction at an as yet unidentified receptor.