3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is a potent direct-acting bacterial mutagen and a rodent carcinogen occurring in chlorine-disinfected drinking water. In this study, we have reacted MX with guanosine, cytidine, thymidine, and calf thymus DNA in aqueous solutions. HPLC analyses of the reaction mixture of MX with guanosine showed that one main product peak was formed. In the reactions of MX with cytidine or thymidine, no product peaks representing base-modified nucleosides could be observed. The product from the MX guanosine reaction mixture was isolated by preparative chromatography on reversed phase C18 columns, and its structure was determined by UV absorbance, 1H and 13C NMR spectroscopy, and mass spectrometry. The product was identified as 3-(beta-D-ribofuranosyl)-7-formylimidazo[1,2-a]purin-9(4H)-one (epsilonfGuo), and the yield for the reaction carried out at pH 7.4 and 37 degrees C was about 0.3 mol %. The adduct could not be observed at the detection limit of five adducts per 10(7) bases in the hydrolysate of the calf thymus DNA reacted with MX. However, this failure does not rule out the possibility that lower amounts of the adduct might be involved in the observed mispairing (adenine incorporated opposite an adducted guanine base) caused by MX in the Salmonella typhimurium strain TA100.