Malonaldehyde was reacted with cytidine in buffered aqueous solutions in the presence of acetaldehyde or formaldehyde. The reaction mixtures were analyzed by HPLC, and the products were isolated by preparative C18 chromatography and structurally characterized by UV absorbance, fluorescence emission, (1)H and (13)C NMR spectroscopy, and mass spectrometry. The major adducts formed in the reaction of malonaldehyde and acetaldehyde were identified as 7-(beta-D-ribofuranosyl)-4-methyl-6-oxo-6,7-dihydro-4H-pyrimido[1,6-a]pyrimidine-3-carbaldehyde (M(1)AA-Cyd) and 1-(beta-D-ribofuranosyl)-4-(3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)pyrimidine (M(2)AA-Cyd). In the reaction of malonaldehyde and formaldehyde, the major product was identified as 7-(beta-D-ribofuranosyl)-6-oxo-6,7-dihydro-4H-pyrimido[1,6-a]pyrimidine-3-carbaldehyde (M(1)FA-Cyd). The highest yields of M(1)AA-Cyd and M(2)AA-Cyd, 3.2 and 0.5 mol %, respectively, were obtained in the reaction performed at pH 4.6 and 37 degrees C for 8 days, while M(1)FA-Cyd was produced at a yield of 0.3 mol % after 3 days of reaction at pH 4.0 and 37 degrees C. The products consist of units derived from malonaldehyde and acetaldehyde (M(1)AA-Cyd and M(2)AA-Cyd) or from malonaldehyde and formaldehyde (M(1)FA-Cyd), and are thus further examples of nucleoside modifications containing structural elements derived from aldehyde condensation reactions. Trace amounts of the adducts may be formed at physiological conditions and may be involved in the mutagenicity of the studied aldehydes.
The reactions of adenosine with malonaldehyde and glyoxal, and with malonaldehyde and methylglyoxal resulted in the formation of one malonaldehyde-glyoxal and one malonaldehyde-methylglyoxal conjugate adduct, respectively. These adducts were isolated and purified by reversed-phase liquid chromatography, and structurally characterized by UV, (1)H- and (13)C-NMR spectroscopy, and mass spectrometry. The malonaldehyde-glyoxal adduct was identified as 8-(diformylmethyl)-3-(beta-D-ribofuranosyl)imidazo[2,1-i]purine (M(1)Gx-A), while the malonaldehyde-methylglyoxal one as 8-(diformylmethyl)-7-methyl-3-(beta-D-ribofuranosyl)imidazo[2,1-i]purine (M(1)MGx-A). Both adducts were also observed in calf thymus DNA when incubated in the respective aldehydes under physiological pH and temperature. Moreover, in the reaction of methylglyoxal and malonaldehyde with adenosine, an additional adduct was formed. This adduct was found to consist of one unit derived from methylglyoxal and one unit from formaldehyde. The adduct was identified as N(6)-(2,3-dihydroxy-2-methylpropanoyl)-9-(beta-D-ribofuranosyl)purine (MGxFA-A). Formaldehyde was found to originate from the commercial methylglyoxal in which it was present as an impurity.
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