ELECTROPHILIC GAMMA-LACTONE KAPPA-OPIOID RECEPTOR PROBES - ANALOGS OF 2'-HYDROXY-2-TETRAHYDROFURFURYL-5,9-DIMETHYL-6,7-BENZOMORPHAN DIASTEREOMERS

Benzomorphans with an electrophilic group in the nitrogen substituent were prepared as potentially irreversible ligands for the kappa-opioid receptor. These were synthesized from products of the reaction of normetazocine with the enantiomers of 5-(iodomethyl)-gamma-butyrolactone (11). alpha-Methylene gamma-lactones 5 and 7 and endocyclic alpha,beta-unsaturated gamma-lactones 8 and 9 were prepared from the corresponding saturated gamma-lactones 13 and 23 possessing the ''active'' (1R,5R,9R)-benzomorphan stereochemistry. Only gamma-lactones 8, 9, 13, and 23, lacking the exocyclic methylene group, retain significant affinities for opioid receptor binding sites when compared with the reference compounds (2''S)-3 and (2''R)-3. As observed with these references compounds, greater binding affinity is also seen with gamma-lactone diastereomers having the 2''S stereochemistry in the nitrogen substituent. Although the gamma-lactones do not bind irreversibly in opioid receptor preparations, they do show kappa-receptor selectivities comparable to those observed for the reference compounds.