14-ALPHA,14'BETA-[DITHIOBIS[(2-OXO-2,1-ETHANEDIYL)IMINO]]BIS (7,8-DIHYDROMORPHINONE) AND 14-ALPHA,14'BETA-[DITHIOBIS[(2-OXO-2,1-ETHANEDIYL)IMINO]]BIS[7,8-DIHYDRO-N-(CYCLOPROPYLMETHYL)NORMORPHINONE] - CHEMISTRY AND OPIOID BINDING-PROPERTIES

14 alpha,14'beta-[Dithiobis[(2-oxo-2,1-ethanediyl)imino]]bis(7,8-dihydromorphinone) (TAMO) (13) was synthesized by condensing 14 beta-amino-7,8-dihydrornorphinone (4) with acetylthioglycolyl chloride and hydrolyzing the resulting ester with mild base Ito give a mixture of the thiol 9 and the disulfide 13. Chromatography of the mixture resulted in conversion of the bulk of the thiol 9 to the disulfide 13 by air oxidation. The disulfide 13 was also prepared by condensing the tert-butyldimethylsilyl ether of 4 with the dithiodiglycolyl chloride and treating the resulting product with F- to give the desired product. The pure thiol 9 free of contamination with the disulfide was prepared by treating 13 with excess N-acetyl-L-cysteine and processing the reaction mixture without resorting to chromatography for purification. The corresponding N-(cyclopropylmethyl) nor compound 15 was prepared from the silyl ether 6 and acetylthioglycolyl chloride followed by hydrolysis, treatment with F-, and air oxidation. Incubation of bovine striatal membranes with 13 and 15 resulted in wash-resistant inhibition of the binding of the mu-selective peptide [H-3][D-Ala(2),(Me)Phe(4),Gly(ol)(5)]-enkephalin (DAMGO). Incubation of membranes with mu but not kappa or delta ligands protected the mu binding sites from alkylation by 13 and 15. The wash-resistant inhibition of mu opioid binding was partially reversed by the addition of the reducing reagent dithiothreitol (DTT). A Scatchard plot of the effect of 13 and 15 on [H-3]DAMGO binding showed that these affinity ligands caused a marked decrease in the B-max value without affecting the K-d value. The wash-resistant inhibition of binding, the reduction in the number of binding sites, the partial reversal of wash-resistant inhibition of binding by DTT, and previously observed long-term antagonism of mu opioid receptors in vivo support the conclusion that 13 and 15 bind covalently to the mu opioid receptor.