Pt(II) complexes of unsubstituted guanine and 7-methylguanine.

In solution, unsubstituted guanine (GH2) is in a tautomeric equilibrium between 1H,7H-keto and 1H,9H-keto forms. Upon coordination with (dien)Pt(II), N9-bound mononuclear complex is preferentially formed. With excess (dien)Pt(II), the dinuclear complex [{Pt(dien)}2(GH-N7,N9)]3+ is formed at basic pH. The X-ray crystal structure analysis of mononuclear complexes [Pt(dien)(GH2-N9)](ClO4)2 x 2.25 H2O (1a), [Pt(dien)(GH2-N9)](Cl)(ClO4) (1b), and the dinuclear complex [{Pt(dien)}2(GH-N7,N9)](ClO4)3 (3) are reported. The N7 linkage isomer [Pt(dien)(GH2-N7)]2+ (2) could not be isolated and was tentatively assigned in solution. In HCl-acidic medium, the dinuclear complex 3 dissociates to form N9 bound mononuclear complex (1) as the major product and presumably the N7 linkage isomer (2) as a minor side product. Species 1 and 3 have been identified by the pD dependence of the 1H NMR guanine resonances. pKa values (calculated for H2O) for deprotonation of the N9 linkage isomer (1a, 1b) are 6.51 +/- 0.01 and 10.53 +/- 0.05 as well as 0.52 +/- 0.07 and 8.55 +/- 0.06 for the dinuclear complex [{Pt(dien)}2(GH-N7,N9)]3+ (3). Ab initio calculations have been performed for [Pt(dien)(GH2-N7)]2+, [Pt(dien)(GH2-N9)]2+ and [{Pt(dien)}2(GH-N7,N9)]3+. They reveal that in gas phase the N7 linkage isomer is more stable than the N9 linkage isomer by DeltaE = 8.4 kcal mol(-1). Reactions with (dien)Pt(II) and cis-(NH3)2Pt(II) were also carried out to study the metal binding behaviour of the ligand, 7-methylguanine (7-MeGH). The complexes [Pt(dien)(7-MeGH-N9)](NO3)(ClO4) (4), cis-[Pt(NH3)2(7-MeGH-N9)2]Cl2 x 2 H2O (5) and cis,cis-[{PtCl(NH3)2}2(7-MeGH-N3,N9)]Cl2 x 3 H2O (6) have been characterized by X-ray crystallography. pKa values for 4 are < 2 and 8.16 +/- 0.04, and for 5 1.86 +/- 0.45 and 8.00 +/- 0.08 (average for deprotonation of two 7-MeGH ligands). Structural peculiarities of N9 platinated guanine ligands are discussed and pKa values of Pt complexes with related guanine nucleobases are compared.

[Refined staging in Hilar bronchial neoplasms with ECG-gated multislice-CT---case report]. / Verfeinertes Staging von hilusnahen Bronchialkarzinomen durch EKG-gegatete Mehrschicht-Spiral-CT--Fallbeschreibung.

Equivocal initial CT-based staging in 2 patients with hilar bronchial neoplasms was reassessed with retrospective ECG-gated Multislice-CT and optimized examination parameters prior to definition of treatment. An initially suspected irresectable T4 tumor with mediastinal infiltration was downstaged to T2 in one case, while tumor infiltration into the left atrium could be confirmed in the other case. In doubtful conditions, ECG-gated multislice CT with optimized examination parameters may be helpful for refined staging in patients with hilar bronchial neoplasms, thus possibly influencing treatment strategies.