Analgesic and other properties of 3: 3-dithienylalkenylamines

Pharmacological characterization of novel synthetic opioids: Isotonitazene, metonitazene, and piperidylthiambutene as potent MU opioid receptor agonists

Recent trends of opioid abuse and related fatalities have highlighted the critical role of Novel Synthetic Opioids (NSOs). We studied the μ-opioid-like properties of isotonitazene (ITZ), metonitazene (MTZ), and piperidylthiambutene (PTB) using different approaches. In vitro studies showed that ITZ and MTZ displayed a higher potency in both rat membrane homogenates (EC₅₀: 0.99 and 19.1 nM, respectively) and CHO-MOR (EC₅₀: 0.71 and 10.0 nM, respectively) than [D-Ala², NMe-Phe⁴, Gly-ol⁵]-enkephalin (DAMGO), with no difference in maximal efficacy (Emax) between DAMGO and NSOs. ITZ also has higher affinity (Ki: 0.06 and 0.05 nM) at the MOR than DAMGO in both systems, whilst MTZ has higher affinity in CHO-MOR (Ki = 0.23 nM) and similar affinity in rat cerebral cortex (Ki = 0.22 nM). PTB showed lower affinity and potency than DAMGO. In vivo, ITZ displayed higher analgesic potency than fentanyl and morphine (ED₅₀: 0.00156, 0.00578, 2.35 mg/kg iv, respectively); ITZ (0.01 mg/kg iv) and MTZ (0.03 mg/kg iv) reduced behavioral activity and increased dialysate dopamine (DA) in the NAc shell (max. about 200% and 170% over basal value, respectively. Notably, ITZ elicited an increase in DA comparable to that of higher dose of morphine (1 mg/kg iv), but higher than the same dose of fentanyl (0.01 mg/kg iv). In silico, induced fit docking (IFD) and metadynamic simulations (MTD) showed that binding modes and structural changes at the receptor, ligand stability, and the overall energy score of NSOs were consistent with the results of the biological assays.

Differences in the stereospecificity of closely related compounds; a reinvestigation of the enantiomers of procyclidine, benzhexol and their metho- and etho-salts

The findings of Duffin & Green (1955) that there are very large differences in the stereospecificity of some closely related phenyl-cyclohexylhydroxypropyl compounds have been confirmed, and it has been shown that this cannot be ascribed to any errors attached to the methods for assessing biological activity, or to inadequate resolution of some of the compounds. Measurement of the affinity constants of the compounds for the postganglionic acetylcholine receptors of the guinea-pig ileum showed that the (+)-and (-)-isomers of benzhexol differ only 5·5-fold in affinity whereas the (+)-and (-)-isomers of procyclidine differ at least 375-fold. This big variation in stereospecificity indicates that changes in one part of the molecule markedly affect the binding of the rest of the molecule and the effects are different in the different enantiomers. It is not possible to interpret the difference between the affinity of the isomers simply in terms of the fit, or failure to fit, of one group, such as the hydroxyl, attached to the asymmetric centre. In the five pairs of compounds tested, the stereospecificity was greatest in the compounds with lowest affinity, which is the reverse of what would be predicted from Pfeiffer's rule.