Preparation and properties of oligodeoxynucleotides containing 5-iodouracil and 5-bromo- and 5-iodocytosine.

The behavior of oligonucleotides containing 5-iodouracil, 5-bromocytidine, and 5-iodocytidine in concentrated ammonia is described. 5-Aminouracil and 5-aminocytidine are obtained as side products when deprotection is performed at 60 degrees C. Small amounts, if any, of side products are obtained when ammonia deprotection is performed at room temperature. The base-pairing properties of these 5-halopyrimidines including triple helix are described.