An experimental reexamination of the reverse anomeric effect in N-glycosylimidazoles

Journal of Organic Chemistry

Volumn 61, Issue 14, 1996, Pages 4514-4515

  Vaino, Andrew R ^a   Chan, Stewart S C ^a   Szarek, Walter A ^a   Thatcher, Gregory R J ^a  

^a QUEEN S UNIVERSITY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000578669     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo960652z     Document Type: Article

References (24)

1. (a) Edwards, J. T. Chem. Ind. (London) 1955, 1102.
2. (b) Lemieux R. U.; Chu N. J. Abstr. Pap. Am. Chem. Soc. 1958, 133, 31N.
3. (c) Thatcher, G. R. J., Ed. The Anomeric Effect and Associated Stereoelectronic Effects; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993.
4. (a) Lemieux, R. U.; Morgan, A. R. Can. J. Chem. 1990, 43, 2205.
5. (b) Lemieux, R. U. Pure Appl. Chem. 1971, 49, 527.
6. (a) Paulsen, H.; Gyorgydeak, Z.; Friedmann, M. Chem. Ber. 1974, 107, 1590.
7. (b) Finch, P.; Nagpurkar, A. G. Carbohydr. Res. 1976, 25, 275.
8. (a) Sinnott M. L. Adv. Phys. Org. Chem. 1988, 24, 113.
9. (b) Kirby, A. J. The Anomeric Effect and Related Stereoelectronic Effects at Oxygen; Springer: New York, 1983.
10. (a) Perrin, C. L.; Armstrong, K. B. J. Am. Chem. Soc. 1993, 115, 6825.
11. (b) Fabian, M. A.; Perrin, C. L.; Sinnott, M. L. J. Am. Chem. Soc. 1994, 116, 8398.
12. Chan, S. S. C.; Szarek, W. A.; Thatcher, G. R. J. J. Chem. Soc., Perkin Trans. 2 1995, 45.
13. 1H NMR data, on pentopyranoses, from Paulsen et al which supports the existence of the RAE", and furthermore, "There is....a growing body of evidence that the RAE.... cannot be generalized as can the anomeric effect". Kirby A. J.; Williams N. H. The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993. Pinto and Leung suggest that "...the term RAE be reserved for those systems for which it was originally defined by Lemieux and Morgan, i.e. systems containing quaternary, nitrogen aromatic substituents". Pinto B. M.; Leung R. Y. N. The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993. Thus the N-glycosylimidazole system represents the crux of the RAE. If there is no RAE in this system, there is no raison d'etre for any extended version of the RAE.
14. 1H NMR data, on pentopyranoses, from Paulsen et al which supports the existence of the RAE", and furthermore, "There is....a growing body of evidence that the RAE.... cannot be generalized as can the anomeric effect". Kirby A. J.; Williams N. H. The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993. Pinto and Leung suggest that "...the term RAE be reserved for those systems for which it was originally defined by Lemieux and Morgan, i.e. systems containing quaternary, nitrogen aromatic substituents". Pinto B. M.; Leung R. Y. N. The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G. R. J., Ed.; ACS Symposium Series 539; American Chemical Society: Washington, DC, 1993. Thus the N-glycosylimidazole system represents the crux of the RAE. If there is no RAE in this system, there is no raison d'etre for any extended version of the RAE.
15. Perrin, C. L.; Fabian, F. A.; Armstrong, K. B. J. Org. Chem. 1994, 59, 5246.
16. Perrin, D. D; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 2nd ed.; Pergamon Press: Toronto, 1980.
17. Bard, A. J.; Faulkner, L. R. Electrochemical Methods; John Wiley & Sons: Toronto, 1980.
18. Conductivity for both species was determined in the presence of 0.5 M N-methylimidazole to ensure dissociation of the TFA and to mimic the conditions of the experiment with the N-glycosylimidazoles.
19. Durette, P. L.; Horton, D. J. Chem. Soc., Chem. Commun. 1969, 516.
20. 3 would not be expected to be identical; however, the use of these values is sufficient to demonstrate clear trends in conformational equilibria.
21. 1H NMR spectrum.
22. Praly, P. L.; Lemieux, R. U. Can. J. Chem. 1987, 65, 213.
23. Grein, F.; Deslongchamps, P. Can. J. Chem. 1992, 70, 1562..
24. 2b,3b Indeed, Perrin has recently concluded that some experimental evidence is compatible with an RAE of electrostatic origin: Perrin, C. L. Tetrahedron 1995, 51, 11901. The influence of the stereochemistry and identity of glycosyl-ring substituents on the conformational equilibrium is not well understood, and the size of such systems has precluded high-level MO calculations. It is not unreasonable that contributions to conformational energy may differ in type and magnitude in the N-(glucopyranosyl)- and N-(xylopyranosyl)-imidazoles such that an RAE, the result of a small electrostatic contribution, is manifest in the latter only.