Reactions in Which the Cycloamyloses Participate Covalently

With the realization that the cycloamyloses form stable monomolecular inclusion complexes in solution came the idea that the inclusion process might affect the reactivity of an organic substrate. This idea was initially pursued by Cramer and Dietsche (1959b) who discovered that the rates of hydrolysis of several mandelic acid esters are enhanced by the cycloamyloses. More recently, the inclusion process has been shown to exert both accelerating and decelerating effects on the rates of a variety of organic reactions. The remainder of this article will be devoted to a discussion of these reactions in an attempt to review, compare, and unify the many intriguing facets of cycloamylose catalysis. 

This differentiation between meta- and para-substituted esters, independent of electronic effects, must be the manifestation of a steric effect associated with the interaction of the esters with the cycloamyloses specifically, inclusion of the ester within the cycloamylose cavity prior to hydro- 

As noted previously, rate accelerations imposed by the cycloamyloses may be competitively inhibited by the addition of inert reagents to the reaction medium. The inhibitor, by competing with the substrate for the cycloamylose cavity, effectively removes a fraction of the catalyst from the reaction coordinate. This observation lends additional force to the mechanism illustrated in scheme I. 

Maximal Rate Constants and Dissociation Constants of Cycloamylose-Phenyl Acetate Complexes b 

Values of /c2 and Kd for the reactions of the cycloamyloses with a variety of phenyl acetates are presented in Table IV. The rate constants are normalized in the fourth column of this table to show the maximum accelerations imposed by the cycloamyloses. These accelerations vary from 10% for p-f-butylphenyl acetate to 260-fold for m-f-butylphenyl acetate, again showing the clear specificity of the cycloamyloses for meta-substituted esters. Moreover, these data reveal that the rate accelerations and consequent specificity are unrelated to the strength of binding. For example, although p-nitrophenyl acetate forms a more stable complex with cyclohexa-amylose than does m-nitrophenyl acetate, the maximal rate acceleration, h/kan, is much greater for the meta isomer. 

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