FORMATION OF A FLUORESCENT ADDUCT IN THE REACTION OF 2'-DEOXYADENOSINE WITH A MALONALDEHYDE-ACETALDEHYDE CONDENSATION PRODUCT

Malonaldehyde (malondialdehyde, MDA) was reacted with 2'-deoxyadenosin e in buffered aqueous solution. HPLC analyses of the reaction mixtures showed that, besides the two previously characterized N-6-propenal (M (1)dA) and N-6-oxazocinyl (M(3)dA) adenine adducts, a third compound e luting at longer retention time was formed. The compound generated a s trong peak in the chromatogram recorded by a fluorescence detector. Th e new compound was isolated by preparative C18 chromatography, and its structure was characterized by UV absorbance, fluorescence emission, H-1 and C-13 NMR spectroscopy, and mass spectrometry. The product was identified as 3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)purine (M(2) AA-dA). The yield of the product was 0.8% following 7 days of reaction at 37 degrees C and pH 4.6. Lower yields were obtained at higher pH c onditions. By the addition of acetaldehyde, the yield increased about 10-fold at all studied pH conditions. The adduct was most likely forme d by an initial condensation of two molecules of malonaldehyde with on e molecule of acetaldehyde followed by reaction of the condensation pr oduct with the exocyclic amino group of 2'-deoxyadenosine, The identif ication of this adduct shows that acetaldehyde may react with DNA base s also through an initially formed malonaldehyde-acetaldehyde condensa tion product.