Reactions of DNA Purines with Dirhodium Formamidinate Compounds That Display Antitumor Behavior

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Abstract

The synthesis and characterization of products from reactions of Rh2(form)2(O2CCF3)2(CH3CN)2 (form = N,N'-p-ditolylformamidinate, N,N'-diphenylformamidinate) and the partially solvated [Rh2(DTolF)2(CH3CN)6][BF4]2 (DtolF = N,N'-p-ditolylformamidinate) with the DNA purine analogues, 9-ethylguanine, and 9-ethyladenine are described. X-ray crystallography was used to characterize Rh2(DTolF)2(O2CCF3)2(CH3CN)2 (1) which crystallizes in the space group P21/n with a = 10.849 (3) Å, b = 21.435 (6) Å, c = 18.677 (3) Å, V = 4340 Å3, Z = 4, R = 0.0451, and Rw = 0.0904. The two rhodium centers are bridged by four O2CCF3- ligands with a Rh−Rh distance of 2.24743(5) Å. Compound 1 reacts with 9-ethylguanine to form Rh2(DTolF)2(9-EtGH)2(O2CCF3)2 (3) which exists as two isomers, namely head-to-head and head-to-tail as confirmed by 1H NMR spectroscopy. [Rh2(DTolF)2(CH3CN)6][BF4]2 (5) crystallizes in the Pbca space group with a = 21.646 (3) Å, b = 31.272 (3) Å, c = 14.561(4) Å, V = 9857 Å3, Z = 8, R = 0.046, and Rw = 0.063. The Rh−Rh bond distance is 2.5594 (8) Å. The partially solvated compound 5 reacts with 9-ethyladenine and 9-ethylguanine to form [Rh2(DTolF)2(9-EtAH)2(CH3CN)][BF4]2 (6) and [Rh2(DTolF)2(9-EtGH)2(CH3CN)][BF4]2 (7), respectively. Compound 6 was characterized by X-ray crystallography as well as by variable temperature 1H NMR spectroscopy. [Rh2(DTolF)2(9-EtAH)2(CH3CN)][BF4]2 crystallizes in the P21/c space group with a = 15.648(8) Å, b = 16.575(5) Å, c = 20.026(8) Å, β = 105.17(4)°, V = 4994 Å3, Z = 4, R = 0.063, and Rw = 0.073. This compound contains two bridging DTolF- ligands as well as two 9-ethyladenine ligands bridging through the N7 and exocyclic N6 positions in a head-to-tail fashion. 1H NMR studies performed on 6 revealed that the N6 position is in the imino (NH-) form.

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