5-Fluorouracil (5-FU) has been shown to be the most reactive among the pyrimidine bases tested for photoreactivity with coumaryl compounds. To see the base specificity of psoralens and 5,7-dimethoxy-coumarin (DMC) in the photoaddition of the compounds to DNA and as a model for the molecular mechanism of photosensitization by psoralens, the photoaddition reaction of DMC to 5-FU is studied.
The major photoadduct is diagnosed and isolated by TLC and column chromatography and purified by recrystallizaation after photolysis of DMC: 5-FU (mole ratio of 1:10) mixture at 360nm in a frozen solution. The structure of isolated photoproduct was identified as a C4-cycloaddition product of DMC and 5-FU by the characteristics of its UV, IR, NMR, mass spectra, and elemental analysis. When the isolated product was irradiated with 254nm light, DMC and 5-FU were obtained as identified by UV (λmax 324nm) and TLC analysis, indicating the photoproduct to be the C4-cycloadduct of DMC and 5-FU.
DMC has no self-quending effect and fluorescence of DMC was not quenched by 5-FU. The photocycloaddition reaction of DMC to 5-FU occurs probably via singlet state, since DMC shows very low efficiency in populating the triplet state and the photodimerization of DMC proceeds exclusively via singlet state in direct irradiation.
5-플루오로 우라실(5-FU)의 쿠마린 화합물과의 광반응성은 비교된 피리미딘 염기중에서 가장 큰것으로 나타났다. 소랄렌의 광독성을 분자적 차원에서 구명하고 쿠마린 화합물들의 DNA에의 광부가반응에서의 염기의 선택성을 알기 위하여, DMC의 5-FU에의 광부가반응을 연구하였다. 주생성물을 TLC로 분석하고 대롱크로마토그래피로 분리하였다. 분리된 생성물의 구조는 UV, IR, NMR, mass 그리고 원소분석 결과에 의해 DMC와 5-FU의 광고리 생성부가반응에 의한 생성물임을 알았다. 분리된 광부가물에 254nm의 빛을 쪼이면 쉽게 원래 물질인 DMC와 5-FU로 쪼개짐을 UV와 TLC로서 확인했다.
DMC는 self-quenching 효과를 볼 수 없으며 TME와 달리 5-FU에 의해서 ？칭되지 않는다. DMC는 삼중상태의 분자밀도가 매우 작고 또 직접 빛을 쪼였을때 이합체화 반응이 주로 단일상태에서 일어나는 점을 볼때 DMC와 5-FU의 광고리 생성부가반응은 단일상태에서 일어날 것으로 추측된다.
