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

The synthesis and characterization of products from reactions of Rh 2 (form) 2 (O 2 CCF 3 ) 2 (CH 3 CN) 2 (form = N,N ‘- p -ditolylformamidinate, N,N ‘-diphenylformamidinate) and the partially solvated [Rh 2 (DTolF) 2 (CH 3 CN) 6 ][BF 4 ] 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 Rh 2 (DTolF) 2 (O 2 CCF 3 ) 2 (CH 3 CN) 2 ( 1 ) which crystallizes in the space group P 2 1 / n with a = 10.849 (3) Å, b = 21.435 (6) Å, c = 18.677 (3) Å, V = 4340 Å 3, Z = 4, R = 0.0451, and R w = 0.0904. The two rhodium centers are bridged by four O 2 CCF 3 - ligands with a Rh−Rh distance of 2.24743(5) Å. Compound 1 reacts with 9-ethylguanine to form Rh 2 (DTolF) 2 (9-EtGH) 2 (O 2 CCF 3 ) 2 ( 3 ) which exists as two isomers, namely head-to-head and head-to-tail as confirmed by 1 H NMR spectroscopy. [Rh 2 (DTolF) 2 (CH 3 CN) 6 ][BF 4 ] 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 Å 3, Z = 8, R = 0.046, and R w = 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 [Rh 2 (DTolF) 2 (9-EtAH) 2 (CH 3 CN)][BF 4 ] 2 ( 6 ) and [Rh 2 (DTolF) 2 (9-EtGH) 2 (CH 3 CN)][BF 4 ] 2 ( 7 ), respectively. Compound 6 was characterized by X-ray crystallography as well as by variable temperature 1 H NMR spectroscopy. [Rh 2 (DTolF) 2 (9-EtAH) 2 (CH 3 CN)][BF 4 ] 2 crystallizes in the P 2 1 / 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 Å 3, Z = 4, R = 0.063, and R w = 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. 1 H NMR studies performed on 6 revealed that the N6 position is in the imino (NH - ) form.