Diastereoisomeric N-tetrahydrofurfurylnoroxymorphones with opioid agonist--antagonist properties.

The two diastereoisomeric N-tetrahydrofurfurylnoroxymorphones and their hydrochlorides 1a and 1b have been prepared and studied pharmacologically; The N-(R)-tetrahydrofurfuryl derivative 1a proved to be an opioid agonist--antagonist and the N-(S)-tetrahydrofurfuryl derivative 1b a pure antagonist. As an analgesic, 1a is 25 times more potent than morphine, but it does not show morphine-like side effects in mice. In withdrawn morphine-dependent rhesus monkeys, 1a only partially suppresses abstinence. Its therapeutic ratio is exceptionally favorable compared with those of morphine and pentazocine. As antagonists, 1a and 1b have comparable potencies of 0.25 and 0.20 of that of nalorphine, respectively, in vivo. In vitro, however, 1a is 28 times (guinea pig ileum) or 6.5 times (mouse vas deferens) more potent than 1b. The antagonist properties of 1a and 1b were not anticipated according to known structure--activity relationships.