THE EFFECTS OF N7-COORDINATED CIS-DIAMMINE-PLATINUM(II) ON THE ACID-BASE PROPERTIES OF GUANINE DERIVATIVES

The effect of the cis-(NH3)(2)Pt2+ unit, if coordinated to the N7 site of guanine residues, on the acid-base properties of complexes of the type cis-(NH3)(2)Pt(9-EtG)(2)(2+), cis-(NH3)(2)Pt(dGuo)(dGMP), or cis- (NH3)(2)Pt(dGMP)(2)(2-), where 9-EtG = 9-ethylguanine, dGuo = 2'-deoxy guanosine, and dGMP(2-) = 2'-deoxyguanosine 5'-monophosphate, is summa rized and various micro acidity constants sue derived, which allow to quantify the intrinsic acidities of H(N1) and -P(O)(2)(OH)(-) sites. I n total the acid-base properties of more than 20 different species are considered. The deprotonation of -P(O)(2)(OH)(-) groups in nucleobase -platinated nucleotide complexes is only slightly facilitated (Delta p K(a) similar or equal to 0.4). The acidification of H(N1) sites by N7- bound platinum(II) is more pronounced, e.g., it amounts on average to Delta pK(a) similar or equal to 0.8 in cis-(NH3)(2)Pt(dGuo)(dGMP). Thi s allows conclusions regarding the situation in intrastrand crosslinks formed between cis(NH3)2Pt2+ and adjacent guanine residues in DNA.