organometallic anticancer complexes
21 narrow to under one minute in width, resulting in only a small loss of resolution (0.47)
Compounds with a ruthenium centre were also analysed. 22, [Ru(η6-‐
flu)(en)Cl]+, and 23, [Ru(η6-‐phent)(en)Cl],+ which are facially chiral and only have a
small difference in their aromatic ligands from fluorene (22) to phenanthrene (23). This is reflected in a maximum difference of 0.28 min between the retention times of the enantiomers eluted first, and only a difference of 0.06 in the resolution of the two chromatograms. Upon separation of the two enantiomers of 22, they remain stable in solution, Fig 3.14. There is a small amount of contamination observed in the chromatogram shown in Fig. 3.14 this is believed to be due to grease from the vacuum line. This stability means that it is possible to scale up the separation and collect enough of each purified enantiomer in order to carry out kinetic studies, cell testing and further experiments required for potential new drugs that are chiral. This is also the case for the Os-‐based complex 18, which has already shown promising activity as a racemic mixture.19
Studies on the other Ru-‐based complex investigated, 24 ([Ru(η6-‐p-‐ cym)(Impy)I]+), show that diasteriomers with two chiral centres, one of which is in the R-‐ configuration, can be separated by chromatographic methods. Studies of the
stability of the separated enantiomers of the Os-‐ and Ru-‐based complexes suggest that the iridium(II) Cp ligands are more labile than the Os(II) and Ru(II) arene ligands.
3.5 Conclusions
In conclusion, the enantiomers and diastereomers of several metal-‐based compounds were separated by chromatographic methods using CHIRALPAK IA and CHIRALPAK IC columns. The stability of some of these enantiomers was also assessed. All of the neutral Ir(Cp*)-‐based complexes tested reverted to a racemic mixture after a minimum of 2 h in solution at approximately 20°C, however, the Ru-‐ and Os-‐based enantiomers maintained stability over 2 or more hours in ethanol at approximately 20°C. Separations of these enantiomers can, in the future, be scaled up to obtain enough material for cell testing and further biological assays.
Small structural differences, such as changing the halide leaving group (complexes 11-‐17), were found to have a substantial effect on the retention time of the enantiomers and the resolution of the separation. Alteration of any of the ligands of the complex was shown to give rise to change in retention times, but the most dramatic changes were caused by the addition of either hydrophillic or hydrophobic groups to the bi-‐dentate ligand. In summary, these studies have provided an important step towareds the preparation of chirally pure organometallic complexes which can undergo clinical development. In prinicle, biological assays can now be carried out using both the racemate and the individual
enantiomers of those compounds which are stable in solution, or only the racemate for those that were shown to be unstable.
3.6 References
1. S. E. Sherman and S. J. Lippard, Chem. Rev., 1987, 87, 1153–1181. 2. A. Pinto and S. Lippard, Biochim. Biophys. Acta, 1985, 780, 167–180. 3. J. Reedijk, Eur. J. Inorg. Chem., 2009, 2009, 1303–1312.
4. P. J. Dyson and G. Sava, Dalt. Trans., 2006, 2006, 1929–1933.
5. F. S. Mackay, J. A. Woods, H. Moseley, J. Ferguson, A. Dawson, S. Parsons, and P. J. Sadler, Chem. Eur. J., 2006, 12, 3155–3161.
6. G. Sava, G. Jaouen, E. a Hillard, and A. Bergamo, Dalt. Trans., 2012, 41, 8226– 8234.
7. A. Casini, C. G. Hartinger, A. A. Nazarov, and P. J. Dyson, Medicinal
Organometallic Chemistry, Springer Berlin Heidelberg, Berlin, Heidelberg, 2010, vol. 32.
8. S. W. Smith, Toxicolo. Sci., 2009, 110, 4–30. 9. FDA, Chirality, 1992, 4, 338–340.
10. K. J. Kilpin, S. M. Cammack, C. M. Clavel, and P. J. Dyson, Dalt. Trans., 2013,
42, 2008–2014.
11. P. Beagley, M. a. L. Blackie, K. Chibale, C. Clarkson, J. R. Moss, and P. J. Smith, J. Chem. Soc. Dalt. Trans., 2002, 2002, 4426–4433.
12. P. Beagley, M. Blackie, and K. Chibale, Dalt. …, 2003, 2003, 3046–3051. 13. B. Chankvetadze, J Chromatogr. A, 1997, 787, 67–77.
14. C. Yamamoto, S. Inagaki, and Y. Okamoto, J. Sep. Sci., 2006, 29, 915–923. 15. B. Chankvetadze, J. Chromatogr. A, 2012, 1269, 26–51.
16. S. N. Paisner and R. G. Bergman, J. Organomet. Chem., 2001, 621, 242–245. 17. T. Nagai, J. Chromatogr. A, 1992, 606, 33–42.
18. P. Sun, A. Krishnan, A. Yadav, S. Singh, F. M. MacDonnell, and D. W. Armstrong, Inorg. Chem., 2007, 46, 10312–10320.
19. Y. Fu, A. Habtemariam, A. M. Pizarro, S. H. van Rijt, D. J. Healey, P. a Cooper, S. D. Shnyder, G. J. Clarkson, and P. J. Sadler, J. Med. Chem., 2010, 53, 8192– 8196.
20. S. D. Shnyder, Y. Fu, A. Habtemariam, S. H. van Rijt, P. a. Cooper, P. M. Loadman, and P. J. Sadler, Medchemcomm, 2011, 2, 666–668.
21. Y. Fu, M. J. Romero, A. Habtemariam, M. E. Snowden, L. Song, G. J. Clarkson, B. Qamar, A. M. Pizarro, P. R. Unwin, and P. J. Sadler, Chem. Sci., 2012, 3, 2485–2494.
22. A. Habtemariam and M. Melchart, J. Med. Chem., 2006, 49, 6858–6868. 23. G. Büchel, I. Stepanenko, and M. Hejl, J. Inorg. Bio. Chem., 2012, 113, 47–54. 24. A. R. Timerbaev, C. G. Hartinger, and B. K. Keppler, Trends Anal. Chem., 2006,
25, 868–875.
25. B. Chankvetadze, C. Yamamoto, and Y. Okamoto, J. Chromatogr. A, 2001,
922, 127–137.
26. B. Chankvetadze, E. Yashima, and Y. Okamoto, J. Chromatogr. A, 1995, 694, 101–109.
27. I. Ali, K. Kumerer, and H. Y. Aboul-‐Enein, Chromatographia, 2006, 63, 295– 307.
28. L. Peng, S. Jayapalan, B. Chankvetadze, and T. Farkas, J. Chromatogr. A, 2010,
1217, 6942–6955.
29. P. Wang, D. Liu, X. Lei, S. Jiang, and Z. Zhou, J. Sep. Sci., 2006, 29, 265–271. 30. K. S. S. Dossou, P. Chiap, B. Chankvetadze, A.-‐C. Servais, M. Fillet, and J.
Crommen, J. Chromatogr. A, 2009, 1216, 7450–7455.
31. F. Gasparrini, I. D’Acquarica, J. G. Vos*, C. M. O’Connor, and C. Villani, Tetrah. Asymm., 2000, 11, 3535–3541.
32. P. Sun, A. Krishnan, A. Yadav, F. M. MacDonnell, and D. W. Armstrong, J. Mol. Struct., 2008, 890, 75–80.
33. G. Atilla-‐Gokcumen and D. Williams, ChemBioChem, 2006, 7, 1443–1450. 34. H. Brunner, Angew. Chem. Int. Ed., 1969, 8, 382–383.
35. H. Brunner and J. Aclasis, Angew. Chem. Int. Ed., 1974, 31, 13–14.
37. H. Brunner, T. Zwack, and M. Zabel, Polyhedron, 2003, 22, 861–865. 38. C. G. Hartinger, M. a Jakupec, S. Zorbas-‐Seifried, M. Groessl, A. Egger, W.
Berger, H. Zorbas, P. J. Dyson, and B. K. Keppler, Chem. Biodiver., 2008, 5, 2140–2155.
39. Z. Liu, A. Habtemariam, A. M. Pizarro, G. J. Clarkson, and P. J. Sadler, Organomet., 2011, 30, 4702–4710.
40. M. J. McKeage, S. J. Berners-‐Price, P. Galettis, R. J. Bowen, W. Brouwer, L. Ding, L. Zhuang, and B. C. Baguley, Cancer Chemother. Pharmacol., 2000, 46, 343–350.
41. Z. Liu, A. Habtemariam, A. M. Pizarro, S. a Fletcher, A. Kisova, O. Vrana, L. Salassa, P. C. a Bruijnincx, G. J. Clarkson, V. Brabec, and P. J. Sadler, J. Med. Chem., 2011, 54, 3011–3026.
42. X. Chen, Y. Okamoto, T. Yano, and J. Otsuki, J. Sep. Sci., 2007, 30, 713–716. 43. I. Romero-‐Canelón, L. Salassa, and P. J. Sadler, J. Med. Chem., 2013, 56,