Formation of conjugate adducts in the reactions of malonaldehyde-acetaldehyde and malonaldehyde-formaldehyde with guanosine.

The reactions of guanosine with malonaldehyde in buffered aqueous solutions in the presence of acetaldehyde or formaldehyde were studied. The reaction mixtures were analyzed by RP-HPLC. Two adducts were formed in the reaction of malonaldehyde and acetaldehyde and one in the reaction of malonaldehyde and formaldehyde. The products were isolated and purified by preparative C-18 chromatography and structurally characterized by UV absorbance, 1H NMR, and 13C NMR spectroscopy and mass spectrometry. The adducts formed in the reaction of malonaldehyde and acetaldehyde were identified as 7-(2,2-diformyl-1-methylethyl)-3-(beta-D-ribofuranosyl)pyrimido[1,2-a]-purin-10(3H)-one (M2AA-Guo I) and 2-(3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)-9-(beta-D-ribofuranosyl)-purin-6(9H)-one (M2AA-Guo II). In the reaction of malonaldehyde and formaldehyde, the major product was identified as 7-formyl-3-(beta-D-ribofuranosyl)pyrimido[1,2-a]purin-10(8H)-one (M1FA-Guo). The highest yields of M2AA-Guo I and M2AA-Guo II, 7 and 2 mol %, respectively, were obtained in the reaction performed at pH 7.4 and 37 degrees C for 6 days, while M1FA-Guo was produced at a yield of 0.3 mol % after 3 days of reaction at pH 7.4 and 37 degrees C. The products are formed by reactions of malonaldehyde-acetaldehyde and malonaldehyde-formaldehyde condensation products with guanosine and are analogous to the previously identified condensation products formed with adenosine, cytidine, and proteins.