Total Syntheses of the Imidazo[1,2‐f]phenanthridine‐containing Alkaloid Zephycandidine A

Isolation, biological activity, and synthesis of isoquinoline alkaloids

Covering: 2019 to 2023Isoquinoline alkaloids, an important class of N-based heterocyclic compounds, have attracted considerable attention from researchers worldwide. To follow up on our prior review (covering 2014-2018) and present the progress of this class of compounds, this review summarizes and provides updated literature on novel isoquinoline alkaloids isolated during the period of 2019-2023, together with their biological activity and underlying mechanisms of action. Moreover, with the rapid development of synthetic modification strategies, the synthesis strategies of isoquinoline alkaloids have been continuously optimized, and the total synthesis of these classes of natural products is reviewed critically herein. Over 250 molecules with a broad range of bioactivities, including antitumor, antibacterial, cardioprotective, anti-inflammatory, neuroprotective and other activities, are isolated and discussed. The total synthesis of more than nine classes of isoquinoline alkaloids is presented, and thirteen compounds constitute the first total synthesis. This survey provides new indications or possibilities for the discovery of new drugs from the original naturally occurring isoquinoline alkaloids.

Tandem Palladium/Copper-Catalyzed Decarboxylative Approach to Benzoimidazo- and Imidazophenanthridine Skeletons

A protocol for a tandem Pd/Cu-catalyzed intermolecular cross-coupling cascade between o-bromobenzoic acids and 2-(2-bromoaryl)-1H-benzo[d]imidazoles or the corresponding imidazoles is presented. The protocol provides conceptually novel and controlled access to synthetically useful N-fused (benzo)imidazophenanthridine scaffolds with high efficiency, a broad substrate scope, and excellent functional group compatibility.

Sensing Magnetic Field and Intermolecular Interactions in Diamagnetic Solution Using Residual Dipolar Couplings of Zephycandidine

An unusual residual dipolar coupling of methylene protons was recorded in NMR spectra because aromatic zephycandidine has preferential orientation at the external magnetic field. The observed splitting contains contribution from the dipole-dipole D-coupling and the anisotropic component of J-coupling. Absolute values of the anisotropy of magnetic susceptibility |Δχ_ax| are larger for protic solvents because of the hydrogen-bonding compared to aprotic solvents for which polar and dispersion forces are more important. The energy barrier for the reorientation due to hydrogen-bonding is 1.22 kJ/mol in methanol-d_4, 0.85 kJ/mol in ethanol-d₆ and 0.87 kJ/mol in acetic acid-d₆. In dimethyl sulfoxide-d₆, 1.08 kJ/mol corresponds to the interaction of solvent lone pair electrons with π-electrons of zephycandidine. This energy barrier decreases for acetone-d₆ which has smaller electric dipole moment. In acetonitrile-d₃, there is no energy barrier which suggests solvent ordering around the solute due to the solvent-solvent interactions. The largest absolute values of the magnetic anisotropy are observed for aromatic benezene-d₆ and tolune-d₈ which have their own preferential orientation and enhance the order in the solution. The magnetic anisotropy of "isolated" zephycandidine, not hindered by intermolecular interaction could be estimated from the correlation between Δχ_ax and cohesion energy density.