A uridine adduct with an ester of the carcinogen 3-hydroxy-1-methylxanthine

The structure of the uridine adduct with the acetate ester of the carcinogen 3-hydroxy-1-methylxanthine has been determined. Covalent binding is between C-8 of xanthine and O-2 of uracil. This was determined from studies of the NMR spectrum, mass spectra and solvolysis in liquid hydrogen sulfide. The nucleoside adduct, formed with uridine, is identical with the adduct with polyuridylic acid after enzymatic hydrolysis. Treatment with aqueous ammonia or pH 7 at 100 degrees C leads to the loss of ribose. Thymidine also forms an adduct with 3-acetoxy-1-methylxanthine in a similar yield. Model studies with a space-filling model suggest that the methylxanthine moiety can fit into the major groove of DNA and cause minimal helix distortion if the thymine base is rotated into the unnatural syn conformation.