Crystallographic studies of piperazine derivatives of 3-methyl-5-spirofluorenehydantoin in search of structural features of P-gp inhibitors

5-Spirofluorenehydantoin derivatives show efflux modulating, cytotoxic and antiproliferative effects in sensitive and resistant mouse T-lymphoma cells. In order to extend the knowledge available about the pharmacophoric features responsible for the glycoprotein P (P-gp) inhibitory properties of arylpiperazine derivatives of 3-methyl-5-spirofluorenehydantoin, we have performed crystal structure analyses for 1-[3-(3′-methyl-2′,4′-dioxospiro[fluorene-9,5′-imidazolidin]-1′-yl)propyl]-4-phenylpiperazine-1,4-diium dichloride monohydrate, C29H32N4O2 2+·2Cl−·H2O (1), 3′-methyl-1′-{3-[4-(4-nitrophenyl)piperazin-1-yl]propyl}spiro[fluorene-9,5′-imidazolidine]-2′,4′-dione, C29H29N5O4·H2O (2), 3′-methyl-1′-{5-[4-(4-nitrophenyl)piperazin-1-yl]pentyl}spiro[fluorene-9,5′-imidazolidine]-2′,4′-dione, C31H33N5O4 (3), and 1-benzyl-4-[5-(3′-methyl-2′,4′-dioxospiro[fluorene-9,5′-imidazolidin]-1′-yl)pentyl]piperazine-1,4-diium dichloride 0.613-hydrate, C32H38N4O2 2+·2Cl−·0.613H2O (4). Structure 3 is anhydrous but the other three structures crystallize with water present. The investigated compounds crystallize in the monoclinic crystal system, with the space group P21/n for 1 and 3, and P21/c for 2 and 4. The cations of salts 1 and 4 are doubly protonated, with the protons located on the N atoms of the piperazine rings. The packing of 1 and 4 in the crystals is dominated by intermolecular N—H...Cl and O—H...Cl hydrogen bonds. In the crystal structure of 2, the intermolecular interactions are dominated by O—H...O and O—H...N hydrogen bonds, while in 3, which is lacking in classic hydrogen-bond donors, it is C—H...O contacts that dominate. Additionally, we have performed induced-fit docking studies for the investigated compounds docked to the P-gp human homology model.