Stereoselective formation of a cyclobutane pyrimidine dimer by using N4-acetyl protection of the cytosine base.

The cytosine base in DNA undergoes hydrolytic deamination at a considerable rate when UV radiation induces formation of a cyclobutane pyrimidine dimer (CPD) with an adjacent pyrimidine base. As a part of our study on the synthesis of CPD-containing oligonucleotides, we have prepared properly-protected thymidylyl-(3' 5')-N(4)-acetyl-2'-deoxycytidine, and the solution of this compound was UV-irradiated using acetophenone as a sensitizer. In this reaction, hydrolysis of the acetylamino group occurred, and a trans-syn cyclobutane thymine-uracil dimer with the syn-anti conformation around the glycosidic bonds was formed stereoselectively.