Photomodification of 4,5',8-trymethylpsoralen (TMP) and related compounds in aqueous solution.

The photomodification of 4,5',8-trimethylpsoralen (TMP) and related compounds was studied in aqueous solution in the presence of oxygen. The capacity of these compounds to generate singlet oxygen was also determined and an evident correlation between the capacity to generate singlet oxygen and the rate constant of the photomodification was observed. Moreover the photomodification was increased in the presence of D2O (which increases the lifetime of singlet oxygen) and quenched in the presence of sodium azide, a well known singlet oxygen quencher. These data support the hypothesis that the photomodification of the examined compounds occurs mainly via singlet oxygen. The role of the photomodification of TMP in relation of therapeutical efficacy is discussed.