Synthesis, Crystal Structure, DFT Analysis and Docking Studies of a Novel Spiro Compound Effecting on EGR-1-Regulated Gene Expression

The spiro compound, 5,5′-dimethoxy-1,3-bis(3-(trifluoromethyl)phenyl)-3,3a-dihydro-1H-spiro[cyclopenta[a]indene-2,2′-indene]-1′,8(3′H,8aH)-dione (4), was synthesized and identified by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Compound 4, C36H26F6O4, was crystallized in the triclinic space group P-1with the cell parameters a = 8.8669(5) Å, b = 10.5298(8) Å, c = 17.0135(11) Å, α = 91.396(2)°, β = 90.490(2)°, γ = 109.235°, V = 1499.14(17) Å3, Z = 2. In an asymmetric unit, two molecules are packed by short contacts to form an inversion dimer. The molecules are linked into chains along the a- and b-axis directions by additional short contacts in the crystal. Compound 4 was synthesized by the dimerization of (E)-5-methoxy-2-(3-(trifluoromethyl)benzylidene)-2,3-dihydro-1H-inden-1-one (3). (E)-5-Methoxy-2-(3-methoxybenzylidene)-2,3-dihydro-1H-inden-1-one (5), one of the analogs of compound 3, was compared with compound 4 based on in vitro experiments, DFT calculations, and an in silico docking study. The HOMO/LUMO energy difference and binding energy difference between the two compounds are consistent with the results obtained from an in vitro assay where 4 showed a better effect than 5. To evaluate the biological activity of 4, we examined its inhibitory effects on Early Growth Respone-1 (EGR-1)-regulated gene expression in HaCaT keratinocytes. Treatment of cells with 4 reduced interleukin-4 (IL-4)-induced thymic stromal lymphopoietin (TSLP) mRNA levels, as revealed by reverse transcription-polymerase chain reaction and quantitative real-time PCR. Furthermore, the electrophoretic mobility shift assay demonstrated that 4 inhibited IL-4-induced DNA binding of EGR-1 to the promoter region of the TSLP gene.