Synthesis and Biological Evaluation of 14-Alkoxymorphinans. Part 9. 14-O-ethyl-5-methylnaltrexone, and opioid antagonist with unusual selectivity

Synthesis and biological evaluation of 14-alkoxymorphinans. 22.(1) Influence of the 14-alkoxy group and the substitution in position 5 in 14-alkoxymorphinan-6-ones on in vitro and in vivo activities

Novel 14-alkoxy-substituted (e.g. allyloxy, benzyloxy, naphthylmethoxy) morphinan-6-one derivatives were synthesized and biologically evaluated. Compounds 6-9 and 11 displayed affinities in the subnanomolar range to mu opioid receptors which were comparable to 14-O-methyloxymorphone (1) and 14-methoxymetopon (3), and higher than oxymorphone (2). Opioid binding affinity was sensitive to the character and length of the substituent in position 14. In smooth muscle preparations they behaved as potent agonists. Antinociceptive potencies of compounds 6-11 in the hot-plate test after sc administration in mice were considerably greater than the potency of morphine. In the colonic propulsion test, the most potent analgesic compound 7 showed negligible constipating activity at the analgesic dose. These findings provide further evidence that the nature of the substituent at position 14 has a major impact on the abilities of morphinans to interact with opioid receptors. Introduction of a 5-methyl group has no significant effect on in vitro biological activities, but resulted in decreased antinociceptive potency.

Synthesis and biological evaluation of 14-alkoxymorphinans. 17. Highly delta opioid receptor selective 14-alkoxy-substituted indolo- and benzofuromorphinans

14-Alkoxy analogues of naltrindole and naltriben differently substituted in positions 5 and 17 and at the indole nitrogen (compounds 28-44) have been synthesized in an effort to enhance the delta potency and/or delta selectivity and in order to further elaborate on structure-activity relationships of this class of compounds. Introduction of a 14-alkoxy instead of the 14-hydroxy group present in naltrindole resulted in somewhat lower delta binding affinity, while in many cases (compounds 31, 34, 37, 40, 41, 44, HS 378) the delta receptor selectivity was considerably increased. An ethoxy group in position 14 is superior to other alkoxy groups concerning delta affinity and selectivity (34, 41, 42, 44, HS 378). In [35S]GTP gamma S binding, compounds 34, 41, and HS 378 exhibited about one-tenth the antagonist potency of naltrindole at delta opioid receptors while their delta antagonist selectivity was considerably higher. 17-Methyl-substituted compounds 35 and 44 were found to be pure delta receptor agonists in this test.

The [4+2]] addition of singlet oxygen to thebaine: new access to highly functionalized morphine derivatives via opioid endoperoxides

The photooxidation of thebaine (3) with a sun lamp affords two main products: hydrodibenzofuran 10 (major) and benzofuran 11 (minor). The latter compound becomes predominant if a Hg lamp is used instead of a sun lamp. The formation of 10 proceeds via an endoperoxide intermediate that undergoes oxidation at the nitrogen atom. Protection of the nitrogen either by protonation or quaternization prevents its oxidation and thus the photooxidation of 3 in acid media constitutes a one-pot procedure for the preparation of 14-hydroxycodeinone 35. Photooxidation of the thebaine ammonium salt 31 allows the isolation in good yields of the corresponding to thebaine endoperoxide 32. The selective protection and reduction of the keto, aldehyde, and olefinic groups of hydrodibenzofuran 10 allowed the preparation of several diol and keto alcohol derivatives. This is the first report on the use of photooxidation to functionalize thebaine at C(6) and C(14) and also the first on the isolation of opioid endoperoxides.

Chemistry of opium alkaloids. Part 44: synthesis and opioid receptor binding profile of substituted ethenoisomorphinans and ethenomorphinans

7- and 8-substituted 6alpha,14alpha-ethenoisomorphinans were synthesized by reaction of properly substituted morphinan-6,8-dienes (analogues of thebaine) with methyl vinyl ketone or ethyl acrylate. Reaction with the appropriate Grignard reagent gave the 7- and 8-dialkylmethanols, respectively. Cleavage of the 3-methyl ether with KOH/glycol or boron tribromide afforded the 3-hydroxyl derivatives. In general, the compounds with the ethoxycarbonyl or dimethylmethanol substituent at the 8alpha-position showed lower affinity for the mu, kappa, and delta opioid receptor subtypes than the corresponding 7alpha- and 7beta-substituted compounds. Introduction of a chloro substituent in position 18 increased the potency significantly. The 7-substituent could be connected to the 18-position without loss of affinity. 5Beta-alkyl substitution of 6alpha,14alpha-ethenoisomorphinans led to a decrease in affinity for the three opioid receptor subtypes. In the 5beta-methyl series the affinity for the mu and delta receptors increased from 7alpha-dimethylmethanol to 7alpha-methylhexylmethanol. In the 5beta-alkyl series, the affinity for the mu-receptor could be increased by connecting the 5- and 7-substituents, yielding a compound with high mu-selectivity. The new 6beta,14beta-ethenomorphinans did not show affinity for any of the opioid receptors, in accordance with the inactivity earlier found in in vivo experiments.