Photochemistry of psoralens

Abstract

The photoreaction of 5, 7-dimethoxycoumarin with adenosine was carried out in dry film state. Photochemical adducts were analyzed by TLC and HPLC. Adducts were isolated by Liophilic Sephadex LH-20 column chromatography. Further separation of products was achieved by preparative HPLC. Two species of photoadducts were obtained and identified as addition products which are formed via diradical intermediate. The major photoadduct was the addition product formed by the attack of 5, 7-dimethoxycoumarin on the amine group of adenosine and in the minor photoadduct, reaction site was hydroxyl groups of ribose. 4``, 5``-Dihydropsoralen was photoreacted with thymine as a model reaction of 4``, 5``-monoadducts of psoralen. Major photoadduct was isolated by solvent extraction and recrystallization and characterized by NMR, IR, UV, mass spectra, and elemental analysis. Photoadduct was identified as $C_4$-cycloaddition adduct and the stereochemistry of the adduct was determined to be syn head-to head by NMR decoupling experiments.