Synthesis of quinolinomorphinan derivatives as highly selective δ opioid receptor ligands

Morphinan Evolution: The Impact of Advances in Biochemistry and Molecular Biology

Morphinan-based opioids, derived from natural alkaloids like morphine, codeine and thebaine, have long been pivotal in managing severe pain. However, their clinical utility is marred by significant side effects and high addiction potential. This review traces the evolution of the morphinan scaffold in light of advancements in biochemistry and molecular biology, which have expanded our understanding of opioid receptor pharmacology. We explore the development of semi-synthetic and synthetic morphinans, their receptor selectivity and the emergence of biased agonism as a strategy to dissociate analgesic properties from undesirable effects. By examining the molecular intricacies of opioid receptors and their signaling pathways, we highlight how receptor-type selectivity and signaling bias have informed the design of novel analgesics. This synthesis of historical and contemporary perspectives provides an overview of the morphinan landscape, underscoring the ongoing efforts to mitigate the problems facing opioids through smarter drug design. We also highlight that most morphinan derivatives show a preference for the G protein pathway, although detailed experimental comparisons are still necessary. This fact underscores the utility of the morphinan skeleton in future opioid drug discovery.

One-pot synthesis of dihydroquinolones by sequential reactions of o-aminobenzyl alcohol derivatives with Meldrum's acids

The functionalized 3,4-dihydroquinolin-2-one nucleus has been assembled in good to high yields through the sequential reaction of readily available N-Ts-o-aminobenzyl alcohols with 5-substituted Meldrum's acid derivatives under mild basic conditions. Highly diastereoselective synthesis of 3-substituted-4-phenyl-1-tosyl-3,4-dihydroquinolin-2(1H)-ones was accomplished from N-(2-(hydroxy(phenyl)methyl)phenyl)-4-methylbenzenesulfonamide under the same reaction conditions. Regarding the reaction mechanism, we hypothesized that the formation of dihydroquinolones proceeds through the in situ generation of aza-o-QMs followed by conjugate addition of enolate/cyclization/elimination of acetone and CO₂.

Into the Fray! A Beginner's Guide to Medicinal Chemistry

Modern medicinal chemistry is a complex, multidimensional discipline that operates at the interface of the chemical and biological sciences. The medicinal chemistry contribution to drug discovery is typically described in the context of the well-recited linear progression of the drug discovery pipeline. However, compound optimization is idiosyncratic to each project, and clear definitions of hit and lead molecules and the subsequent progress along the pipeline becomes easily blurred. In addition, this description lacks insight into the entangled relationship between chemical and pharmacological properties, and thus provides limited guidance on how innovative medicinal chemistry strategies can be applied to solve optimization problems, regardless of the stage in the pipeline. Through discussion and illustrative examples, this article seeks to provide insights into the finesse of medicinal chemistry and the subtlety of balancing chemical properties pharmacology. In so doing, it aims to serve as an accessible and simple-to-digest guide for anyone who wishes to learn about the underlying principles of medicinal chemistry, in a context that has been decoupled from the pipeline description.

Synthesis and Biological Evaluation of 1,3-Dideazapurine-Like 7-Amino-5-Hydroxymethyl-Benzimidazole Ribonucleoside Analogues as Aminoacyl-tRNA Synthetase Inhibitors

Aminoacyl-tRNA synthetases (aaRSs) have become viable targets for the development of antimicrobial agents due to their crucial role in protein translation. A series of six amino acids were coupled to the purine-like 7-amino-5-hydroxymethylbenzimidazole nucleoside analogue following an optimized synthetic pathway. These compounds were designed as aaRS inhibitors and can be considered as 1,3-dideazaadenine analogues carrying a 2-hydroxymethyl substituent. Despite our intentions to obtain N¹-glycosylated 4-aminobenzimidazole congeners, resembling the natural purine nucleosides glycosylated at the N⁹-position, we obtained the N³-glycosylated benzimidazole derivatives as the major products, resembling the respective purine N⁷-glycosylated nucleosides. A series of X-ray crystal structures of class I and II aaRSs in complex with newly synthesized compounds revealed interesting interactions of these “base-flipped” analogues with their targets. While the exocyclic amine of the flipped base mimics the reciprocal interaction of the N³-purine atom of aminoacyl-sulfamoyl adenosine (aaSA) congeners, the hydroxymethyl substituent of the flipped base apparently loses part of the standard interactions of the adenine N¹ and the N⁶-amine as seen with aaSA analogues. Upon the evaluation of the inhibitory potency of the newly obtained analogues, nanomolar inhibitory activities were noted for the leucine and isoleucine analogues targeting class I aaRS enzymes, while rather weak inhibitory activity against the corresponding class II aaRSs was observed. This class bias could be further explained by detailed structural analysis.

The Synthesis of 5-Amino-dihydrobenzo[b]oxepines and 5-Amino-dihydrobenzo[b]azepines via Ichikawa Rearrangement and Ring-Closing Metathesis

The combination of Ichikawa's rearrangement and a ring-closing metathesis reaction of allyl carbamates is presented as a method for the preparation of 5-amino-substituted 2,5-dihydro-benzo[b]oxepines, 2,5-dihydro-benzo[b]azepines, and 2,5-dihydro-benzo[b]thiepins. It was demonstrated that the use of nonracemic allyl carbamates enables the synthesis of enantioenriched benzo-fused seven-membered heterocycles. Finally, it was shown that further functionalization of the obtained structures allows access to pharmacologically active 5-amino-substituted 2,3,4,5-tetrahydro-1-benzo[b]oxepine scaffolds.

The role of methoxy substituents in regulating the activity of selenides that serve as spirodioxyselenurane precursors and glutathione peroxidase mimetics

A series of o-(hydroxymethyl)phenyl selenides containing single or multiple methoxy substituents was synthesized, and the rate at which each compound catalyzed the oxidation of benzyl thiol to its disulfide with excess hydrogen peroxide was measured. This assay provided the means for comparing the relative abilities of the selenides to mimic the antioxidant selenoenzyme glutathione peroxidase. The mechanism for catalytic activity involves oxidation of the selenides to their corresponding selenoxides with hydrogen peroxide, cyclization to spirodioxyselenuranes, followed by reduction with two equivalents of thiol to regenerate the original selenide with concomitant disulfide formation. A single p-methoxy group on each aryl moiety afforded the highest catalytic activity, while methoxy groups in the meta position had little effect compared to the unsubstituted selenide, and o-methoxy groups suppressed activity. The installation of multiple methoxy groups on each aryl moiety provided no improvement. These results can be rationalized on the basis of dominating mesomeric and steric effects of the p- and o-substituents, respectively.

A microwave-assisted multicomponent synthesis of substituted 3,4-dihydroquinazolinones

A series of structurally diverse 3,4-dihydroquinazolinones was synthesized via a novel cascade imine/cyclization/aza-Henry reaction in moderate to excellent yields.

The most effective influence of 17-(3-ethoxypropyl) substituent on the binding affinity and the agonistic activity in KNT-127 derivatives, δ opioid receptor agonists

We investigated the structure-activity relationship of KNT-127 (opioid δ agonist) derivatives with various 17-substituents which are different in length and size. The 17-substituent in KNT-127 derivatives exerted a great influence on the affinity and agonistic activity for the δ receptor. While the compounds with electron-donating 17-substituents showed higher affinities for the δ receptor than those with electron-withdrawing groups, KNT-127 derivatives with 17-fluoroalkyl groups (the high electron-withdrawing groups) showed high selectivities for the δ receptor among evaluated compounds. In addition, the basicity of nitrogen as well as the structure of the 17-N substituent such as the length and configuration at an asymmetric carbon atom contributed to agonist properties for the δ receptor. Thus, the analog with a 17-(3-ethoxypropyl) group showed the best selectively and potent agonistic activity for the δ receptor among KNT-127 derivatives. These findings should be useful for designing novel δ selective agonists.