Solvolysis of charged active esters of carboxylic acids with cyclo (l- or d-Glu-l-His) |
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Authors: | Masao Tanihara Yukio Imanishi |
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Affiliation: | Department of Polymer Chemistry, Kyoto University, Yoshida Honmachi, Sakyo, Kyoto 606, Japan |
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Abstract: | Cyclic dipeptide cyclo(l- or d-Glu-l-His) carrying an anionic site and a nucleophilic site has been synthesized and used as a catalyst for the solvolysis of cationic esters in aqueous alcohols. In the solvolysis of 3-acyloxy-N-trimethylanilinium iodide (S+n, n = 2 and 10) and Cl?H3N+(CH2)11COOPh(NO2), no efficient nucleophilic catalysis was observed. On the other hand, in the solvolysis of Gly-OPh(NO2)·HCl, Val-OPh(NO2)·HCl and Leu-OPh(NO2)·HCl a very efficient general base-type catalysis by cyclo(l-Glu-l-His) was observed. In particular, with the latter two substrates the catalysis by cyclo(l-Glul-His) was more efficient than that by imidazole, although the catalysis was not enantiomer-selective. The diastereomeric cyclic dipeptide cyclo(d-Glu-l-His) was almost inactive under the same conditions. Confomation of cyclo(l- or d-Glu-l-His) in aqueous solution was investigated and the structure/catalysis relationship is discussed. |
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Keywords: | Esters (carboxylic) conformation solvolysis cationic ester electrostatic binding general-base catalysis |
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