SYNTHESIS AND PHOTOCHEMICAL CLEAVAGE OF CIS-SYN PYRIMIDINE CYCLOBUTANE DIMER ANALOGS

The synthesis of cis-syn cytosine-cytosine and cytosine-thymine cyclobutane dimer analogs are described. In contrast to the thymine and uracil cyclobutane dimers, the cytosine-containing dimers have significant absorption bands in the UV-B region of the spectrum. These dimers can be reverted back to their monomeric form (split) by irradiation with UV Light. Additionally, the dimers can be split by photochemical electron transfer. Use of excited state electron donors N,N-dimethylaniline and N,N,N,N-tetramethylbenzidine gives high yields of the monomeric pyrimidines-even at high conversions. Use of excited-state electron accepters, 2-anthraquinonesulfonate and 9,10-dicyanoanthracene also resulted in efficient splitting. However the conversion-corrected chemical yields for these splitting reactions is much lower, due to the formation of a large number of side products.