Advanced Strategies for Enhancing Nitroxide Stability and Synthesis: Redox Properties and Mechanisms

1. Syntheses and Redox Properties of Sterically Shielded Nitroxides of Imidazoline, Imidazolidine, Pyrroline and Pyrrolidine Series

2. 2 Nitroxide reduction consequences • Spin probe decay • Low molecular weight antioxidants depletion • Toxicity

3. 3 How to increase the nitroxide lifetime • Delivery systems • Liposomes • Inclusion complexes • Bulky substituents

4. 4 Reduction in the rat blood I.A.Kirilyuk, A.A.Bobko, I.A.Grigor’ev, V.V. Khramtsov, Org.Biomol.Chem., 2004, 2, 1025 Influence of bulky substituents Observed rates of reduction with ascorbate at pH 5.5. [nitroxide] 1 mM, [ascorbic acid] 100 mM L. Marx, R. Chiarelli, T. Guiberteau and A. Rassat, J. Chem. Soc. Perkin Trans. 1, 2000, 1181-1182. 0.027 s-1 0.0009 s-1

5. 5 Syntheses of sterically shielded nitroxides

6. 6 Organometallic Compounds Additions. pH-Sensitive Spin Probes pK 6.60 (37 °C) A. A. Bobko, T. D. Eubank, J. L. Voorhees, O. V. Efimova, I. A. Kirilyuk, S. Petryakov, D. G. Trofimiov, C. B. Marsh, J. L. Zweier, I. A. Grigor’ev, A. Samouilov, and V. V. Khramtsov, Magn. Reson. Med., 2012, 67, 1827-1836. D. A. Komarov, I. Dhimitruka, I. A. Kirilyuk, D. G. Trofimiov, I. A. Grigor’ev, J. L. Zweier, V. V. Khramtsov, Magn. Reson. Med., 2012, 68, 649–655.

7. 7 Organometallic compounds additions. Limitations metallation low reactivity deoxygenation

8. 8 Organometallic compounds additions. Nitroxides with tert-butyl group at α-carbon

9. 9 Organometallic compounds additions. Nitroxides with tert-butyl group at α-carbon

10. 10 Condensations 9% pK = 6.1 kred = 0.04 V. V. Yan’shole, I. A. Kirilyuk, I. A. Grigor’ev, S. V. Morozov, and Yu. P. Tsentalovich, Russian Chemical Bulletin, Vol. 59, No. 1, pp. 66—74.

11. 11 1,3-Dipolar cycloaddition C. Sár, J. Jekő, K. Hideg, Synthesis, 2003, 9, 1367-1372 C. Sár, E. Ősz, J. Jekő, K. Hideg, Synthesis, 2005, 2, 255-259

12. 12 Intramolecular 1,3-dipolar cycloaddition D. A. Morozov, I. A. Kirilyuk, D. A. Komarov, A. Goti, I. Yu. Bagryanskaya, N. V. Kuratieva, I. A. Grigor’ev. J. Org. Chem. 2012, 77 (23), pp. 10688-10698.

13. 13 EPR spectra of pyrrolidine nitroxides 1 mM solutions in H2O+10%DMSO; spectrometer settings: modulation amplitude, 0.5 G; microwave power, 10 mW; time constant, 20 ms; sweep time, 40 s.

14. 14 EPR line widths problem A.A. Bobko, I.A. Kirilyuk, N.P. Gritsan, D.N. Polovyanenko, I.A. Grigor’ev, V.V. Khramtsov, E.G. Bagryanskaya, ApplMagnReson (2010) 39:437–451.

15. 15 Partly deuterated nitroxides R=CH3 (1/3); CD3 (2/3).

16. 16 Paletta, J. T.; Pink, M.; Foley, B.; Rajca, S.; Rajca, A.; Synthesis and Reduction Kinetics of Sterically Shielded PyrrolidineNitroxides. Org. Lett. 2012, Vol.14, No.20, P. 5322-5325.

17. 17 Mechanism of nitroxides reduction with ascorbate A.A.Bobko, I.A.Kirilyuk, I.A.Grigor’ev, J.L.Zweier, V.V.Khramtsov. FreeRadic. Biol. Med., 2007, V. 42, P. 404-412. k = 5*10-3 M-1c-1

18. 18 Rate constants of nitroxides reduction with ascorbate 0.02 0.005

19. 19 Rate constants of reduction with ascorbate, k1, M-1s-1 6.32±0.01 0.044±0.002 5.6±0.2 0.039±0.003 0.063±0.002 0.001 Paletta, J. T.; Pink, M.; Foley, B.; Rajca, S.; Rajca, A.; Synthesis and Reduction Kinetics of Sterically Shielded PyrrolidineNitroxides. Org. Lett. 2012, Vol.14, No.20, P. 5322-5325.

20. 20 Rate constants of imidazolidine nitroxides reduction with ascorbate

21. 21 Correlation between the rate constants of nitroxide reductionwith ascorbate(kAsc) and the coupling constants with 1-(tert-butoxycarbonyl)-ethyl radical (kc)

22. 22 Rate constants of direct and reverse reactions A.A.Bobko, I.A.Kirilyuk, I.A.Grigor’ev, J.L.Zweier, V.V.Khramtsov. FreeRadic. Biol. Med., 2007, V. 42, P. 404-412.

23. Hydrogen atom exchange 23 NR CPH-15N PСА-15N 0.04 0.02