Photoreaction of 4,5',8-trimethylpsoralen with adenosine

Photoreaction of 5-methoxypsoralen with thymidine. Isolation and characterization of a pyrone-side monoadduct involving the pyrimidine methyl group

The UVA-mediated photoreaction of 5-methoxypsoralen (5-MOP) with thymidine has been investigated in the dry state. Under these conditions, the main products are 5-MOP pyrone-side monoadducts to thymidine. We report the isolation and characterization of an unusual 5-MOP-thymidine photoproduct. The assignment of the photoadduct was achieved on the basis of extensive spectroscopic measurements (UV, mass spectrometry (MS), 1H and 13C nuclear magnetic resonance (NMR), nuclear Overhauser effect (NOE) experiments). The formation of the photoadduct, which is rationalized in terms of a radical mechanism, appears to involve, in a covalent bond, the C-4 pyrone moiety of 5-MOP and the methyl group of thymidine.

Adenosine-mediated photoreaction of 4,5',8-trimethylpsoralen with alcohols

Irradiation of thin films consisting of 4,5',8-trimethylpsoralen (TMP), adenosine and small amounts of alcohols led to TMP-alcohol photoadducts in addition to TMP-adenosine photoadducts. Four TMP-ethanol and two TMP-methanol adducts have been separated and characterized. Covalent bonds were formed between the 4-carbon of TMP and the alpha-carbon to the hydroxy group in the alcohols. The TMP-alcohol photoadducts were formed only in the TMP film containing small amounts of alcohol and adenosine. Furthermore, no photoadduct of TMP and ribose was detected upon photolysis of a TMP-ribose film, suggesting that the adenine moiety plays a specific role in the reaction. The interaction of adenosine with psoralens in a dry film may be related to the DNA sequence selectivity observed for the photoreaction of psoralens with DNA.

Transient absorption spectra and quenching of coumarin excited states by nucleic acid bases

Triplet-triplet absorption spectra of coumarin show different profiles and maxima in ethanol from those in water, which are very similar to those reported in benzene. Long-lived transient species other than triplet states were generated as initial photoproducts between coumarins and nucleic acid bases. The excited singlet and triplet states of coumarins were quenched by nucleic acid bases. Adenine base quenched the excited singlet state of coumarins more efficiently than thymine base. However, photocycloadducts of furocoumarins are formed predominantly with thymine, and not with adenine. Moreover, it is reported that the poly[dA-dT].poly[dA-dT] sequence region is the most favourable site for the photocycloaddition reaction of furocoumarins. The results imply that adenine contributes to singlet-state photocycloaddition reaction of furocoumarins with thymine, probably through an adenine-furocoumarin-thymine termolecular interaction.

A novel photoadduct of 4,5',8-trimethylpsoralen and adenosine

A novel photoadduct of 4,5',8-trimethylpsoralen (TMP) and adenosine was isolated and purified by reverse-phase liquid chromatography. The structure of the photoproduct was determined by various spectral methods and found to be a TMP-adenosine 1:1 adduct resulting from the covalent bond formation between the carbon C(4) of TMP and ribose 4'-carbon of adenosine.