Interligand CH · · · π interaction in binary cobalt(III) complexes of N-pyridoxy-L-amino acids. Biological significance of the pyridoxal 2-methyl group

Abstract

Reaction of K₃[Co(CO₃)₃] with 2 equivalents of N-pyridoxy-L-amino acid (pyridoxy = 3-hydroxy-5-hydroxymethyl-2-methylpyridin-4-ylmethyl; amino acid = alanine, leucine, phenylglycine, phenylalanine, p-nitrophenylalanine, p-methoxyphenylalanine, or tryptophan) afforded the bis(N-pyridoxy-L-amino acidato)cobalt(III) complex as a single band on anion-exchange chromatography. Each complex has been isolated as its sodium salt and characterized in aqueous solution by UV/VIS circular dichroism (CD), and ¹H NMR spectra and by X-ray crystallographic analysis in the solid state. The cobalt(III) atom is co-ordinated to two trans(N)-meridional N-pyridoxy-L-amino acid ligands. The 2-methyl group of one pyridoxal moiety lies over the aromatic ring of another pyridoxal ring with separations of 3.67 and 3.56 Å. The ¹H NMR resonance of the 2-methyl group shows an upfield shift when compared with that of the free pyridoxyamino acid. The selective formation of the trans(N)-meridional-Λ-[R(N), R(N)] diastereoisomer is interpreted in terms of an interligand CH · · · π interaction. The CD and ¹H NMR spectra suggest that addition of 1 equivalent HCl weakens this interaction. The biological significance of the pyridoxy 2-methyl group in vitamin B₆ coenzyme is discussed.

References

1. B. Alberts, D. Bray, J. Lewis, M. Raff, K. Roberts and J. D. Watson, Molecular Biology of the Cell, Garland Publishing, New York, 3rd edn., 1994, p. 89.
2. E. Frieden, J. Chem. Educ., 1975, 52, 754.
3. W. P. Jencks, Adv. Enzymol. Relat. Areas Mol. Biol., 1975, 43, 219.
4. S. K. Burley, P. R. David, A. Taylor and W. N. Lipscomb, Proc. Natl. Acad. Sci. USA, 1990, 87, 6878.
5. S. K. Burley, P. R. David, R. M. Sweet, A. Taylor and W. N. Lipscomb, J. Mol. Biol., 1992, 224, 113.
6. H. Kim, S. K. Burley and W. N. Lipscomb, J. Mol. Biol., 1993, 230, 722.
7. S. K. Burley, P. R. David, R. M. Sweet and W. N. Lipscomb, Proc. Natl. Acad. Sci. USA, 1991, 88, 6919.
8. T. Mizutani, T. Ema, T. Tomita, Y. Kuroda and H. Ogoshi, J. Am. Chem. Soc., 1994, 116, 4240.
9. H. Masuda, A. Odani, T. Yamazaki, T. Yajima and O. Yamauchi, Inorg. Chem., 1993, 32, 1111.
10. K. Jitsukawa, T. Morioka, H. Masuda, H. Ogoshi and H. Einaga, Inorg. Chim. Acta, 1994, 216, 249.
11. O. Yamauchi, A. Odani, H. Masuda and H. Sigel, Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, New York, 1996, vol. 32, p. 207.
12. Y. Kodama, K. Nishihata, M. Nishio and Y. Iitaka, J. Chem. Soc., Perkin Trans. 2, 1976, 1490.
13. H. Okawa, Coord. Chem. Rev., 1988, 92, 1.
14. M. Levitt and M. F. Perutz, J. Mol. Biol., 1988, 201, 751.
15. M. Nishio and M. Hirota, Tetrahedron, 1989, 45, 7201.
16. M. Nishio, Y. Umezawa, M. Hirota and Y. Takeuchi, Tetrahedron, 1995, 51, 8665.
17. E. Fischer and H. Sigel, J. Am. Chem. Soc., 1980, 102, 2998.
18. K. Kobayashi, Y. Asakawa, Y. Kikuchi, H. Toi and Y. Aoyama, J. Am. Chem. Soc., 1993, 115, 2648.
19. K. Jitsukawa, K. Iwai, H. Masuda, H. Ogoshi and H. Einaga, Chem. Lett., 1994, 303.
20. D. M. Smith, N. R. Thomas and D. Gani, Experimentia, 1991, 47, 1104.
21. A. M. Catherine, G. V. Michel and N. J. Johan, J. Mol. Biol., 1992, 225, 495.
22. P. A. Clark, J. N. Jansonius and E. L. Mehler, J. Am. Chem. Soc., 1993, 115, 1894.
23. P. A. Clark, J. N. Jansonius and E. L. Mehler, J. Am. Chem. Soc., 1993, 115, 9790.
24. P. Christen and D. E. Metzler(Editors), Transaminases, Wiley, New York, 1985.
25. K. Dakshinamurti, Ann. N.Y. Acad. Sci., 1990, vol. 585.
26. J. Kielland, J. Am. Chem. Soc., 1973, 59, 1675.
27. J. A. Ibers and W. C. Hamilton(Editors), International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4.
28. MOLEN, An Interactive Structure Solution Procedure, Enraf-Nonius, Delft, 1990.
29. J. E. Fergusson, Stereochemistry and Bonding in Inorganic Chemistry, Prentice-Hall, New York, 1974.
30. K. Jitsukawa, T. Yamamoto, H. Masuda and H. Einaga, unpublished work.
31. E. H. Abbott and A. E. Martell, J. Am. Chem. Soc., 1969, 91, 6866.
32. E. H. Abbott and A. E. Martell, J. Am. Chem. Soc., 1970, 92, 5845.
33. M. Noritake, K. Okamoto, J. Hidaka and H. Einaga, Bull. Chem. Soc. Jpn., 1990, 63, 353.
34. R. J. Motekaitis, Y. Sun and A. E. Martell, Inorg. Chim. Acta, 1989, 159, 29.
35. C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976.
36. L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, 3rd edn., NY, 1960.
37. C. E. Johnson and F. A. Bovey, J. Chem. Phys., 1958, 29, 1012.
38. T. Yasui, J. Hidaka and Y. Shimura, J. Am. Chem. Soc., 1965, 87, 2762.