Specific affinity labeling of μ opioid receptors in rat brain by S-activated sulfhydryldihydromorphine analogs

S-Activated sulfhydryldihydromorphine analogs 1 and 2 were synthesized. In the rat brain receptor binding assays, both 1 and 2 exhibited considerably high affinities for μ opioid receptors (IC50; 1= 31.1 nM, 2= 10.7 nM). However, when each analog was incubated with membranes for the purpose of getting disulfide bridgings, 1 (EC50 = 58 nM) was found to affinity-label the μ receptors about 30 times more effectively than 2 (EC50 = 1700 nM).