(The) photoreactivities of 8-MOP thymidine 4',5'-monoadducts and 5,7-dimethoxycoumarin to thymidine

Abstract

The 8-MOP<4`` 5``, 5 6>thymidine and DMC-thymidine photocycloadducts were formed on irradiation of the 8-MOP-thymidine and DMC-thymidine mixture with 350 nm light in dry film state. The products were separated by dry silica gel column chromatography or flash column chromatography. Unreacted thymidine could be removed much efficiently with this procedure than the conventional thin layer chromatography and liquid chromatography. The 4``,5``-monoadducts(F-2-A and F-2-B) of 8-MOP and thymidine separated were characterized by UV, IR, $^1H$-NMR and CD spectra and DMC-thymidine adducts by comparing with authentic samples. Some photophysical properties of the 8-MOP<4`` 5``, 5 6>thymidine were investigated. The fluorescence maximum and quantum yield of the 4``,5``-monoadducts are largely dependent on solvent polarity and the ratio of the phosphorescence to fluorescence quantum yields ($\Phi_p/\Phi_f$) was significantly influenced by the external heavy atoms. The relative reactivities of photocycloaddition of the 8-MOP<4`` 5``, 5 6>thymidine monoadduct and DMC with thymidine in dry film state were investigated to elucidate the photosensitization mechanism. DMC disappeared faster than the 4``5``-monoadduct and the rate increment of DMC-thymidine adducts formation along irradiation time is relatively greater than that of F-2-B - thymidine, i.e., biadducts formation.