Photochemical Reactions of Cytosine N‐methyl Analogs in Alcoholic Solution

Abstract— –The photochemical reactions of 1‐methylcytosine (la), 1, N4‐dimethylcytosine (Ib), and 1, N4. N4‐trimethylcytosine (Ic) in isopropanol have been investigated. In all three reactions addition of isopropanol occurs across the 5,6‐double bond of the pyrimidine ring. For example, in the case of Ir photo‐reaction with isopropanol leads to formation of 5,6‐dihydro‐6–(2‐hydroxy‐2‐propyl)‐l, N4, N4‐trimethylcytosine (IIc). In all three reactions 5,6‐dihydro‐l‐methyluracil (III) was also isolated as a product; in the case of Ic, 5,6‐dihydro‐1, N4, N4‐trimethylcytosine (IV) was isolated as well. Evidence is presented that indicates cytosine, cytidine, and 2',3'‐isopropylidene cytidine also form adducts with isopropanol. Photoinduced reaction of Ic with ethanol leads to formation of 5.6‐dihydro‐6–(l‐hydroxy‐l‐ethyl)‐l, N4. N4‐trimethylcytosine (V). Both acetone sensitization and di‐t‐butyl peroxide initiated free radical reactions of Ib with isopropanol leads to formation of an adduct identical to that formed in the unsensitized photochemical reaction of Ib with isopropanol.