Abstract
Abstract— 3‐Carbethoxypsoralen (3‐CPs) has been tested in the photochemotherapy of psoriasis. It only forms monoadducts with DNA and is being considered as a non‐carcinogenic alternative to 8‐MOP which itself forms DNA crosslinks that arc difficult to repair. Using laser flash photolysis or pulse radiolysis, the triplet state of 3‐CPs, a possible intermediate in photosensitization, has been generated in several solvents: ethanol, water and benzene. The triplet lifetime, extinction coefficient and quantum efficiency of formation have been measured. Triplet reactivities towards (i) the solvents used, (ii) 3‐CPs, (iii) oxygen, (iv) tryptophan and (v) tyrosine, leading, respectively, to photoadditions with water, ethanol and 3‐CPs, to 1O2, semioxidized tryptophan and semioxidized tyrosine, (vi) thymine and (vii) uracil have been investigated. The dark binding of 3‐CPs to DNA has been studied by comparing the reactivity of eaq‐ with free 3‐CPs, free DNA and the 3‐CPs DNA complex. Some photophysical and photochemical properties of 4′,5′di‐hydro‐3‐carbethoxypsoralen(DH–3‐CPs), model of the main fluorescent photo‐product of 3‐CPs, have also been investigated. Biological consequences of the photochemical properties of 3‐CPs andDH–3‐CPs have been studied in a cellular system (haploid yeast).
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