The 5,6-double bond of pyrimidine nucleosides, a fragile site in nucleic acids.

Our studies have revealed reagents that can attack the 5,6-double bond of pyrimidine nucleosides; potassium permanganate and bisulfite. This review is a personal account of these studies, with a discussion on the vulnerable nature of this particular double bond to external nucleophiles and oxidizing agents. The finding that N(4)aminocytidine, produced on treatment of cytidine with bisulfite and hydrazine, is a strong mutagen is also described.