Isolation and Characterization of Two Furan‐side Photoadducts of 7‐Methylpyrido[3,4‐c] Psoralen to the Sugar Moiety of 2‐Deoxyadenosine†

Abstract

Abstract. The UVA‐mediated photoreaction of the monofunctional 7‐methylpyrido[3,4‐c]psoralen (MePyPs) with 2′‐deoxy‐adenosine was investigated in the dry state. Two main 7‐methylpyrido[3,4‐c]psoralen monoadducts to 2′‐deoxy‐adenosine were isolated by HPLC and characterized by soft ionization mass spectrometry (fast atom bombardment) and extensive 1H NMR analyses including correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser effect measurements. The two unusual photoadducts exhibit a covalent bond between the C‐4′ of the furan moiety of the psoralen on one hand and either the C‐l' or the C‐4′ of the furanose ring of the purine nucleoside on the other hand. The furan‐side monoadducts appear to be specific for both 2′‐deoxy‐adenosine and MePyPs. They are likely to result from the recombination of the 4′,5′‐dihydrofuran‐4′‐yl radical of MePyPs with 2′‐deoxyadenosyl carbon‐centered sugar radicals at either the 1′ or the 5′ position.