Aryl phosphate complexation by cationic cyclodextrins. An enthalpic advantage for guanidinium over ammonium and unusual enthalpy-entropy compensation

Organic Letters

Volumn 2, Issue 23, 2000, Pages 3575-3578

  Hauser, Steven L ^a   Johanson, Eric W ^a   Green, Heather P ^a   Smith, Paul J ^a  

^a UNIVERSITY OF MARYLAND   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CYCLODEXTRIN; GUANIDINE; ORGANOPHOSPHATE; QUATERNARY AMMONIUM DERIVATIVE;

ARTICLE; CHEMICAL STRUCTURE; CHEMISTRY; THERMODYNAMICS;

CYCLODEXTRINS; GUANIDINE; MODELS, MOLECULAR; PHOSPHORIC ACID ESTERS; QUATERNARY AMMONIUM COMPOUNDS; THERMODYNAMICS;

EID: 0034676529     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol006503r     Document Type: Article

References (25)

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12. This idea is consistent with recent experiments examining the binding of arginine and lysine by calixarenes substituted with four to eight sulfonate groups. It was found that in all cases arginine binding with a given calixarene occurred with greater loss in entropy. Douteau-Guével, N.; Coleman, A. W.; Morel, J.-P.; Morel-Desrosiers, N. J. Chem. Soc., Perkin Trans. 2 1999, 629-633.
13. Experiments with monocationic cyclodextrins would arguably provide a more direct comparison. However, calorimetric titrations of monoammonium and monoguanidinium β-CD derivatives with phenyl phosphate failed to provide heats sufficient for quantitation. We were also unable to detect binding between a monoguanidinium β-CD derivative and phosphotyrosine using competitive spectroscopy (ref 4b). These results underscore the weak nature of ionic bonds in aqueous environments, where both cations and anions are effectively solvated. The use of dicationic hosts complicates interpretation of the results somewhat in that both groups may not form energetically equivalent interactions with the phosphate moiety within a complex.
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15. The syntheses of 2 and 4 are reported in ref 4b. Compounds 1 and 3 were prepared by analogous chemistry, starting with a 6A,6C-disulfonate of β-CD (Cuchinotta, V.; D'Alessandro, F.; Impellizzeri, G.; Vecchio, G. Carbohydr. Res. 1992, 224, 95-102). Diamides 7 and 8 were prepared using published methods: Burke, T. R., Jr.; Barchi, J. J., Jr.; George, C.; Wolf, G.; Shoelson, S. E.; Yan, X. J. Med. Chem. 1995, 38, 1386-1396.
16. The syntheses of 2 and 4 are reported in ref 4b. Compounds 1 and 3 were prepared by analogous chemistry, starting with a 6A,6C-disulfonate of β-CD (Cuchinotta, V.; D'Alessandro, F.; Impellizzeri, G.; Vecchio, G. Carbohydr. Res. 1992, 224, 95-102). Diamides 7 and 8 were prepared using published methods: Burke, T. R., Jr.; Barchi, J. J., Jr.; George, C.; Wolf, G.; Shoelson, S. E.; Yan, X. J. Med. Chem. 1995, 38, 1386-1396.
17. Calorimetric measurements were made using a MicroCal VP-ITC isothermal titration calorimeter; equilibrium constants and enthalpies were obtained from the primary data using the software supplied by MicroCal. More details and representative primary data are available as Supporting Information.
18. With unmodified β-CD, a similar increase in association constant on going from phenylalanine to an uncharged amide of phenylalanine has been observed: Rekharsky, M. V.; Schwarz, F. P.; Tewari, Y. B.; Goldberg, R. N. J. Phys. Chem. 1994, 98, 10282-10288.
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25. 6, respectively (Reichardt, C. Solvents and Solvent Effects in Organic Chemistry, 2nd ed.; VCH: Weinheim, 1990; pp 9-13). The shapes of the corresponding potential functions indicate that changes in r, such as those resulting from dymanic motion within a complex, will have a smaller effect on the interaction energy of two ionic groups than it will on two dipoles or nonpolar groups.