Synthesis of biflavones and their interaction with DNA

To explore new biflavones, 7-hydroxy-8-hydroxymethyl-4'-methoxyisoflavone (1), (5, 7-dihydroxyflavone-8-yl)-(7'-hydroxy-4''-methoxyisoflavone-8'-yl)methane (2), bis(7-hydroxy-4'-methoxyflavone-8- yl) methane (3), bis(3', 5'-diisopropyl-7, 4'-dihydroxyisoflavone-8-yl)methane (4), and bis(7-hydroxyisoflavone- 8-yl) methane (5) were designed and synthesized from chrysin, formononetin, 7, 4'-dihydroxy-3', 5'-diisopropyl- isoflavone and 7-hydroxyisoflavone.  Their structures were identified with IR, ¹H NMR, ¹³C NMR and elemental analysis.  The binding of 1−5 with DNA was studied with fluorescent spectroscopy.  Compounds 2−5 showed higher binding affinity with DNA than 1.  According to the Stern-Volmer equation, the binding constants of 2, 3 were determined at 35 ℃ and 25 ℃ respectively, they were K_q2 (25 ℃) = 1.95 × 10⁴ L·mol⁻¹ and K_q2 (35 ℃) = 1.67 × 10⁴ L·mol⁻¹; K_q3 (25 ℃) = 1.89 × 10⁴ L·mol⁻¹ and K_q3 (35 ℃) = 1.58 × 10⁴ L·mol⁻¹.  The quenching mechanism of 2, 3 was suggested as static quenching.