PHTHALOCYANINE AND NAPHTHALOCYANINE PHOTOSENSITIZED OXIDATION OF 2'-DEOXYGUANOSINE - DISTINCT TYPE-I AND TYPE-II PRODUCTS

The photodynamic properties of the di- and tetrasulfonated zinc and aluminium phthalocyanines and a tetrasulfonated aluminium napththalocyanine were studied using 2'-deoxyguanosine as a DNA model compound. The major photooxidation products of this nucleoside were identified and classified according to their formation through a radical mechanism (type I) or a singlet oxygen mediated mechanism (type II). The major type I product was obtained and identified as 2,2-diamino-[( 2-deoxy-beta-D-erythropentofuranosyl)-4-amino]-5(2H)-oxazolone. Two major type II products were characterized as the 4R* and 4S* diastereomers of 9-(2-deoxy-beta-D-erythropentofuranosyl)-7,8-dihydro-4-hydroxy-8-oxoguanine. In addition a third product, also resulting from a type II photooxidation, was identified as 8-oxo-7,8-dihydro-2'-deoxyguanosine. Quantification of these products provided a means to estimate the contribution of type I and type II pathways during the phthalocyanine and naphthalocyanine mediated photooxidation of 2'-deoxyguanosine, confirming the major role of singlet oxygen in these processes.