New iodine derivatives of flavonol and isoflavone

Abstract

The reaction of the flavonol 3,7,3 , 4 -tetra-O-methylquercetin (1) and of the isoflavone 7,4 -di-O-methylgenistein (2) with alkaline iodine in methanol afforded four new iodine derivatives: 8-iodo-5-hydroxy-3,7,3 , 4 -tetramethoxyflavone (1a) and 6-iodo-5-hydroxy-3,7,3 , 4 -tetramethoxyflavone (1b) from 1; 2 afforded a mixture of two compounds, identified as a racemic mixture of (±)-trans-5-hydroxy-2,3,7,4 -tetramethoxy-8-iodo-isoflavanone (2a) and (±)-trans-5-hydroxy-2,3,7,4 -tetramethoxy-6,8-diiodo-isoflavanone (2b). The formation of these different products reveals a significant difference involving the chemical interaction between the reactive site of α, β-unsaturated ketones of flavonol and isoflavone under the tested reaction conditions (using I 2 /KOH/MeOH). Furthermore, the trans stereoselectivity is noteworthy in the nucleophylic addition of methanol at the isoflavone α, β-unsaturated system. The structures were identified on the basis of spectral data, mainly 1D and 2D NMR and mass spectra.