Substitution of inosine and guanosine 5′-monophosphate for chloride, and water on PdII(polyaminopolycarboxylate) complexes: mechanistic controls in forming PdII(pac)L or PdII(pac)L2 products

Inhibitory effects of the guanine moiety on Suzuki couplings of unprotected halonucleosides in aqueous media

In the Suzuki arylations of unprotected halonucleosides in aqueous media, 8-bromo-2'-deoxyguanosine (8BrdG) couplings were slower to reach completion than the corresponding 8-bromo-2'-deoxyadenosine (8BrdA) couplings. The guanine moiety has an acidic proton, which under our Suzuki conditions (pH congruent with 10) may be deprotonated to give an anion that can coordinate to palladium. The possibility that guanine coordination was responsible for the observed slower rates was explored using additive experiments in which nonhalogenated nucleosides were added to the Suzuki coupling reaction of 8BrdA or 4-bromotoluene and PhB(OH)2 and the reaction progress monitored by HPLC or GC. Adding dG slowed these reactions, and an induction period was observed. The addition of dA or 1-methyl-2'-deoxyguanosine (1MedG) to these couplings did not affect the rate of conversion to product. Guanine coordination was further explored using 13C and 31P NMR spectroscopy, which implies that guanine is coordinating to palladium through N-1 or O-6, or both. Furthermore, the presence of dG inhibited the formation of the active palladium(0) catalytic species, which may account for both the observed induction period and the sluggishness of reactions where guanine is involved.

Studies on the interaction of altromycin B and its platinum(II) and palladium(II) metal complexes with calf thymus DNA and nucleotides

The interaction of the anticancer antibiotic altromycin B and its isostructrural Pt(II) and Pd(II) metal complexes with native calf thymus (CT) DNA was studied using UV-thermal denaturation experiments, circular dichroism spectroscopy and temperature controlled spectrophotometric titrations. Altromycin B stabilizes the double helix by raising the T(m), mainly by intercalation of its chromophore between the base pairs and interacting electrostatically via its sugar moieties with the edges of the DNA helix. Moreover, altromycin B induces a B-->A structural transition of CT DNA. The effect on DNA stability and conformation depends on the metal ion. Pt(II) and Pd(II) complexes induce the B-->A structural transition and stabilize the double helix similarly but they present lower final hyperchromicity due to premelting effects which were caused by intra- and interstrand crosslinking. Thus, a synergic effect of the metal ions to altromycin B-CT DNA interaction is observed in both cases. Altromycin B interacts with 5'-GMP, 5'-AMP and 5'-CMP by electrophilic attack of the opened epoxide ring to the N(7)G, N(1)/N(7)A and N(3)C. Thus, covalent binding between these nucleotides and altromycin B takes place and explain the multiple binding mode suggested by the studies of the interaction of altromycin B and its complexes with DNA. The [Pd(II)-altroB] complex dissociates in the presence of the nucleotides, and various species of Pd(II)-nucleotide complexes, especially with 5'-GMP, are formed. The [Pt(II)-altroB] complex dissociates too, but only one or two species of Pt(II)-nucleotide complexes are formed, and in the case of 5'-AMP interaction the formation of a tertiary altroB-Pt(II)-5'AMP complex is proposed. 5'-TMP reacts very weakly in comparison with the other three nucleotides. These interactions were followed by 1H-NMR.