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INTERACTIONS AND PHOTOREACTIVITY OF 5‐ALKOXYPSORALENS WITH THYMINE. A MODEL APPROACH
Author(s) -
Décout JeanLuc,
Huart Georges,
Lhomme Jean
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02868.x
Subject(s) - psoralen , chemistry , intramolecular force , adduct , thymine , photochemistry , double bond , ring (chemistry) , chromophore , stereochemistry , dna , organic chemistry , biochemistry
— In order to investigate the interactions and the photoreactions in solution between the thymine (thy) and the psoralen (Pso) rings, we have prepared model compounds Thy‐(CH 2 ) n ‐Pso in which two aromatic chromophores Thy and Pso are linked by flexible polymethylene chains of varying length (CH 2 ) n . Two series of compounds were examined and compared as models for the two important drugs 5‐methoxypsoralen and 8‐methoxypsoralen. Results concerning the 5‐alkoxypsoralen series are reported here. In water, these model molecules exhibit intramolecular ring‐ring stacking interactions as indicated by hypochromism in the UV and by shielding of the protons in 1 H NMR spectroscopy. These interactions disappear in organic solvents. The photochemical properties of the models were examined in relation with their ground state interaction properties. Irradiation at 365 nm carried out at the usual concentrations (10 ‐2 ‐10 ‐3 M) leads exclusively to a stereoselective dimerization involving the psoralen moieties of the models at the 3,4 double bonds. However, when operating at exceedingly low concentrations (2 × 10 ‐5 M ), the psoralen photodimerization is avoided and a highly regio and stereo‐selective psoralen thymine photoaddition is observed involving the 3,4 double bond of psoralen leading to the cis adduct. The same reaction occurs for all models under study being independent of the length of the (CH 2 ) n polymethylene linking chain, n = 2 to 6, 12 and of the solvent used. This is unambiguous proof for the highest intrinsic photoreactivity of the 3,4 vs the 4′,5′ double bond in 5‐alkoxy psoralen.