Synthesis, molecular modeling, DFT studies, and enantioseparation of tetrahydro-4H-chromene derivatives with calcium channel blocking activity

Calcium channel blockers are considered effective therapeutics in cardiovascular and neurological disorders. Herein, we replaced the nitrogen atom of 1,4-dihydropyridines (DHPs), the most popular group of calcium channel blockers, with oxygen to yield 4H-pyrans. The target compounds (EA1-EA3) were obtained by the reaction of 4,4-dimethyl-1,3-cyclohexanedione, substituted benzaldehyde, malononitrile, and excess ammonium acetate in ethanol in which ammonium acetate functioned as a catalyst rather than a reactant resulting in the formation of tetrahydrochromenes over hexahydroquinolines. After confirming their proposed chemical structures, the title compounds were tested on two types of calcium channels, L-type (Ca_v1.2) and T-type (Ca_v3.2), to determine whether physiological activity was still maintained after this bioisosteric substitution. According to the data obtained from patch-clamp experiments, EA1 and EA3 carrying lipophilic halogens on C-4 phenyl ring were found to be more effective inhibitors of both calcium channels compared to EA2 with a nitro group at the same position. Molecular docking studies and molecular dynamics simulations were conducted on EA1 in Ca_v1.2 to investigate the binding mode of tetrahydro-4H-chromenes in the DHP binding site. EA1 achieves a binding pose similar to other DHPs in L-type channels. Density functional theory (DFT) vibrational frequency calculations were carried out for all synthesized compounds to assist in assigning the bands observed in the experimental IR spectra. Additionally, electrostatic potential (ESP) map analysis was utilized to visualize the charge distributions within the molecules. Frontier molecular orbital visualizations were employed to examine the reactivity of the compounds, along with other chemical parameters such as the HOMO-LUMO gap, electronegativity, global chemical hardness, and global softness. Finally, enantioseparation of EA1-EA3 was carried out on chiral stationary phases in three different chromatographic modes.