Opioid binding and in vitro profiles of a series of 4-hdroxy-3-methoxyindolomorphinans. Transformation of a delta-selective ligand into a high affinity kappa-selective ligand by introduction of a 5,14-substituted bridge

Synthesis and SAR study of opioid receptor ligands: mono- and bis-indolomorphinans

Mono- and bis-indolomorphinans were synthesized through a multi-step synthetic approach from the alkaloid, thebaine, to further explore the C-ring SAR (structure-activity relationship) of morphinan scaffold. Both mono-indoles displayed good binding affinity and selectivity for the delta receptor, with compound 6b possessed the highest K(i) value of 1.45 nm at this receptor. Bisindolomorphinans 7a,b did not have appreciable affinity for both delta and kappa receptors, but moderate binding at the mu receptor was observed. Functional assays indicated that the newly synthesized mono-indole 6b was delta-agonist, opposite to the delta-antagonist profile of naltrindole. Bisindoles 7a,b were mu-agonists. This work further confirms that the phenol component in opioids is essential for higher binding to the opioid receptors. The different binding ability, receptor selectivity, and the functional activity profiles of naltrindole 2, monoindole 6b, and bisindole 7b clearly indicated that they interact with the opioid receptors in different modes.

3-Hydroxy-4-methoxyindolomorphinans as delta opioid selective ligands

Previous studies showed that 4-hydroxy-3-methoxyindolomorphinans had variable delta opioid affinity and selectivity. Herein, we show that the 3,4-dimethoxy analogs possessed similar low affinity, whereas the 3-hydroxy-4-methoxy analogs showed excellent delta opioid affinity and selectivity comparable with the parent indolomorphinans.

3D–QSAR studies of orvinol analogs as κ-opioid agonists

Orvinols are potent analgesics that target opioid receptors. However, their analgesic mechanism remains unclear and no significant preference for subtype opioid receptor has been achieved. In order to find new orvinols that target the kappa-receptor, comparative 3D-QSAR studies were performed on 26 orvinol analogs using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). The best predictions for the kappa-receptor were obtained with the CoMFA standard model (q2 = 0.686, r2 = 0.947) and CoMSIA model combined steric, electrostatic, hydrophobic, and hydrogen bond donor/acceptor fields (q2 = 0.678, r2 = 0.914). The models built were further validated by a test set made up of seven compounds, leading to predictive r2 values of 0.672 for CoMFA and 0.593 for CoMSIA. The study could be helpful for designing and prepare new category kappa-agonists from orvinols.

Opioid ligands with mixed mu/delta opioid receptor interactions: an emerging approach to novel analgesics

Opioids are widely used in the treatment of severe pain. The clinical use of the opioids is limited by serious side effects such as respiratory depression, constipation, development of tolerance, and physical dependence and addiction liabilities. Most of the currently available opioid analgesics exert their analgesic and adverse effects primarily through the opioid mu receptors. A large number of biochemical and pharmacological studies and studies using genetically modified animals have provided convincing evidence regarding the existence of modulatory interactions between opioid mu and delta receptors. Several studies indicate that delta receptor agonists as well as delta receptor antagonists can provide beneficial modulation to the pharmacological effects of mu agonists. For example, delta agonists can enhance the analgesic potency and efficacy of mu agonists, and delta antagonists can prevent or diminish the development of tolerance and physical dependence by mu agonists. On the basis of these observations, the development of new opioid ligands possessing mixed mu agonist/delta agonist profile and mixed mu agonist/delta antagonist profile has emerged as a promising new approach to analgesic drug development. A brief overview of mu-delta interactions and recent developments in identification of ligands possessing mixed mu agonist/delta agonist and mu agonist/delta antagonist activities is provided in this report.

Molecular modeling and 3D-QSAR studies of indolomorphinan derivatives as kappa opioid antagonists

Molecular modeling and 3D-QSAR studies were performed on 31 indolomorphinan derivatives to evaluate their antagonistic behaviors on kappa opioid receptor and provide information for further modification of this kind of compounds. Best predictions were obtained with CoMFA standard model (q2 = 0.693, N = 4, r2 = 0.900) and CoMSIA combined model (q2 = 0.617, N = 4, r2 = 0.904). Both models were further validated by an external test set of eight compounds with satisfactory predictions: r2 = 0.607 for CoMFA and r2 = 0.701 for CoMSIA. In addition, the 3D structure of human kappa opioid receptor was constructed based on the crystal structure of bovine rhodopsin, and the CoMSIA contour plots were then mapped into the structural model of kappa opioid receptor-GNTI complex to identify key residues, which might account for kappa antagonist potency and selectivity. The roles of nonconserved Glu297 and conserved Lys227 of human kappa opioid receptor were then discussed.

Synthesis and opioid receptor binding properties of a highly potent 4-hydroxy analogue of naltrexone

Very high affinity for opioid receptors (e.g., K(i)=0.052nM for mu) has been observed in the rationally designed naltrexone analogue 5. SAR and physical data supports the hypothesis that the 4-OH group of 5 stabilizes the 3-carboxamido group in the putative bioactive conformation.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain as isoquinoline system, together with napthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids with the structures of new bases, together with their reactions and syntheses, are reported. The literature from July 2003 to June 2004 is reviewed, with 145 references cited.