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

The synthesis of cis-syn cytosine-cytosine and cytosine-thymine cyclob utane dimer analogs are described. In contrast to the thymine and urac il 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 elect ron transfer. Use of excited state electron donors N,N-dimethylaniline and N,N,N,N-tetramethylbenzidine gives high yields of the monomeric p yrimidines-even at high conversions. Use of excited-state electron acc epters, 2-anthraquinonesulfonate and 9,10-dicyanoanthracene also resul ted in efficient splitting. However the conversion-corrected chemical yields for these splitting reactions is much lower, due to the formati on of a large number of side products.