14α,14'β-[Dithiobis[(2-oxo-2,1-ethanediyl)imino]]bis(7,8- dihydromorphinone) and 14α,14'β-[dithiobis[2-oxo-2,1- ethanediyl]imino]]bis[7,8-dihydro-N-(cyclopropyl-methyl)normorphinone]: Chemistry and opioid binding properties

Article abstract of DOI:10.1021/jm00037a008

14α,14'β-[Dithiobis[2-oxo-2,1-ethanediyl)imino]]bis(7,8- dihydromorphinone) (TAMO) (13) was synthesized by condensing 14β-amino-7,8- dihydromorphinone (4) with acetylthioglycolyl chloride and hydrolyzing the resulting ester with mild base to 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 μ-selective peptide[³H][D-Ala²,(Me)Phe⁴,Gly(ol)⁵]- enkephalin (DAMGO). Incubation of membranes with μ but not κ or δ ligands protected the μ binding sites from alkylation by 13 and 15. The wash- resistant inhibition of μ 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 [³H]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 μ opioid receptors in vivo support the conclusion that 13 and 15 bind covalently to the μ opioid receptor.