3-UREIDOACRYLONITRILES - NOVEL PRODUCTS FROM THE PHOTOISOMERIZATION OF CYTOSINE, 5-METHYLCYTOSINE, AND RELATED-COMPOUNDS

During studies of the effects of far-ultraviolet light on DNA and its components, we have discovered that cytosine and 5-methylcytosine, as well as their nucleosides and N1-methyl derivatives, undergo photoisomerization reactions to yield the corresponding cis- and trans-3-ureidoacrylonitriles. For example, N1-methylcytosine reacts to give cis- and trans-3-[N3-methylureido]acrylonitrile. These products have been characterized through use of one- and two-dimensional high-resolution 1H and 13C NMR spectroscopy, ultraviolet and infrared spectroscopy, electron impact and liquid secondary ion mass spectrometry, and, in some cases, synthesis by an alternate route. Detailed 13C NMR data for the parent compounds are presented for comparison purposes. These photoisomerization reactions take place cleanly in acetonitrile; the corresponding reactions occur in aqueous solution as well. For cytosine and 5-methylcytosine the photoreaction in acetonitrile is slow; however, the rate of reaction is greatly enhanced by N1 substitution. We determined the quantum yields for formation of the products derived from 2′-deoxycytidine to be 2.44 ⨯ 10-4 in water and 1.34 ⨯ 10-3 in acetonitrile. The mechanism of formation of the 3-ureidoacryionitriles is proposed to involve initial formation of a N3-C6 Dewar structure, followed by a ring-opening rearrangement. © 1990, American Chemical Society. All rights reserved.