Isolation and characterization of the mono-heterodimers of 8-methoxypsoralen and thymidine involving the pyrone moiety

Abstract

The photoreaction of 8-methoxypsoralen (MeO 8 Pso), a bifunctional psoralen, with thymidine (dThd) as a DNA model has been investigated in the dry state. Eight major photoproducts have been isolated by reversed phase high performance liquid chromatography. These products have been characterized as mono-heterodimers by UV, 1 H-NMR, circular dichroism and electron impact mass spectrometry. The cyclobutyl structure of these products was further confirmed by the well-known photoreversal reaction. The MeO 8 Pso < > dThd heterodimers were shown to involve exclusively the pyrone ring of MeO 8 Pso. The two cissyn diastereoisomers of MeO 8 Pso < > dThd were preferentially produced, with relatively minor quantities of cis-anti and trans-syn isomers. The instability of these photoproducts in aqueous solutions may account for their reversal to generate the parent dThd.