Photoreaction of 5,7-dimethoxycoumarin with adenosine

Abstract

The photoreaction of 5,7-dimethoxycoumarin (DMC) with adenosine, has been studied. The photoreaction was carried out in a dry film state formed by quick evaporation of methanol solvent the DMC and adenosine solution. Two products among photoadducts were isolated by Lobar RP-8 column chromatography and preparative HPLC. The main products of photoreaction have been characterized by spectroscopic methods using UV, $^1H$ NMR, IR and mass spectrometry. Two photoadducts were not photosplitted by short wavelength UV light, and $λ_max$ at 260 nm which is the same as that of adenosine. It indicates that adenosine chromophore remains unchanged, strongly suggesting that the photoadducts are not a $C_4$-cycloaddition product. Photobinding of DMC occurs to adenosine through covalent bond formation between the pyrone ring of DMC and the sugar ring moiety of adenosine. A reasonable mechanism may be a radical intermediate.