Elucidation of the Active Conformation of Antiproliferative Sulfonamides, 5N-Arylsulfonyl-1,5-benzodiazepin-2-ones

Fentanyl-Type Antagonist of the μ-Opioid Receptor: Important Role of Axial Chirality in the Active Conformation

In recent years, synthetic opioids have emerged as a predominant cause of drug-overdose-related fatalities, causing the "opioid crisis." To design safer therapeutic agents, we accidentally discovered μ-opioid receptor (MOR) antagonists based on fentanyl with a relatively uncomplicated chemical composition that potentiates structural modifications. Here, we showed the development of novel atropisomeric fentanyl analogues that exhibit more potent antagonistic activity against MOR than naloxone, a morphinan MOR antagonist. Derivatives displaying stable axial chirality were synthesized based on the amide structure of fentanyl. The aS- and aR-enantiomers exerted antagonistic and agonistic effects on the MOR, respectively, and each atropisomer interacted with the MOR by assuming a distinct binding mode through molecular docking. These findings suggest that introducing atropisomerism into fentanyl may serve as a key feature in the molecular design of future MOR antagonists to help mitigate the opioid crisis.

Synthesis and Atropisomeric Properties of Benzoazepine-Fused Isoindoles

Atropisomeric, bench-stable benzoazepine-fused isoindoles were synthesized via oxidation from isoindoline precursors. Using the isoindoles 5d-f as models, the stereochemistry and conformational folding of the systems were examined. Chiral UHPLC was used to analyze the rate of racemization and calculate the Gibbs free energy of enantiomerization (ΔG^‡_Enant). X-ray crystallography, ¹H NMR spectroscopy, and DFT calculations were used to elucidate the three axes of chirality and clarify the structural factors contributing to ΔG^‡_Enant. Tandem rotation around the axes of chirality precludes the formation of diastereomers, with rotational restriction of the C_aryl-N_sulfonamide bond determined as the moderator of atropisomeric stability in the system, affected primarily by steric hindrance as well as by π-stacking interactions facilitated by the folded conformation of the sulfonamide over the isoindole moiety.

Atropodiastereoselective 5N-Acylation of 1,5-Benzodiazepin-2-ones with (S)-2-Phenylpropanoyl and (S)-2-Phenylbutanoyl Chlorides

5N-Acylation of 1N-methyl-1,5-benzodiazepin-2-ones with (S)-2-phenylpropanoyl and (S)-2-phenylbutanoyl chlorides afforded the (a¹S,a²S,S)-atropisomer (I) diastereoselectively over the (a¹R,a²R,S)-isomer (II) in the ratio of 1:0.06-0.15. The preferential formation of I may be explained by the thermodynamically preferable π-π stacking interaction between two benzene rings in the benzodiazepine ring and the acyl chloride during the reaction. Analysis using ab initio calculations (RI-MP2/6-31+G(d) level of theory) for the acylation reaction indicated the π-π stacking interaction in the transition state. Furthermore, isomer I was shown to be thermodynamically more stable than II. The higher stability of I may be caused by the folded form of the two benzene rings, which was revealed by NMR, X-ray, and computational analyses.

Stereogenic and conformational properties of medium-ring benzo-fused N-heterocycle atropisomers

Medium-ring (7-9-membered) benzo-fused N-heterocycles - a core structure in several important pharmaceuticals - have a diverse range of interesting conformational and stereochemical properties which arise from restricted bond rotation in the non-aromatic ring. The atropisomers of these pharmaceutically relevant N-heterocycles typically exhibit different biological activities, warranting the need to deeply understand the factors controlling the conformation and stereochemistry of the systems. Beginning with a brief introduction to atropisomer classification, this review will detail a number of medium-ring benzo-fused N-heterocycle systems from the recent literature to provide an overview of structural factors which can affect the atropisomeric nature of the systems by altering the overall conformation and rate of stereo-inversion. As well as general factors such as ring-size and sterics, the impact of additional stereocentres in these systems will be addressed. This includes the differences between sulfur, nitrogen and carbon stereocentres, and the consequences of stereocentre placement around the N-heterocycle ring. Further, conformational stabilisation via non-covalent intramolecular bonds will be explored. As such, this review represents a significant resource for aiding in the design, synthesis and study of new and potentially bioactive medium-ring benzo-fused N-heterocycles.