Structural and antivirial studies of dipetalactone and its methyl derivative

Dipetalactone (6,6,10,10-tetramethyl-6H,10H-dipyranocoumarin) and its C4-methyl derivative have been synthesized and structurally studied. The structures of these compounds, explored on the basis of 1D and 2D NMR techniques in solution and the DFT/B3LYP calculations for the single molecule of dipetalactone, are in good agreement with those found in the crystals. In the tetracyclic dipetalactones the central coumarin ring systems are nearly planar and the pyran rings adopt a distorted sofa conformation. ompounds crystallize with two symmetry independent molecules, A and B. The π-stacking is the main force stabilizing the pairs of centrosymmetric dimers, A⋅A and B⋅B. These dimers interact via the intermolecular CH⋯O and CH⋯π hydrogen bonds forming three-dimensional supramolecular frameworks which are nearly isostructural. The MP2 calculations reveal that the dimers of dipetalactone only slightly distort during the crystal formation as compared with those in the gas phase. The energy increase upon such a distortion was estimated as ca. 4 kcal mol−1. In addition, the binding energy for the dimer was found to be ca. 20 kcal mol−1. lactone and its methyl derivative were examined for cytotoxicity as well as anti-HIV activity.