Exceptional gas-phase enantioselectivity of chiral tetramide macrocycles |
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Authors: | Filippi Antonello Gasparrini Francesco Pierini Marco Speranza Maurizio Villani Claudio |
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Institution: | Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive. Università La Sapienza, 00185 Roma, Italy. |
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Abstract: | Diastereomeric proton-bound complexes between some phenylalanine derivatives (A) and chiral tetramide macrocycles (M) exhibit an uncommon enantioselectivity when reacting with the enantiomers of 2-aminobutanes in the gas phase (B). The measured enantioselectivity depends mainly on two distinct factors: (i) the configuration of the A guest; and (ii) the structure and the relative stability of isomeric MHA]+ complexes. No significant effects of the B configuration are observed. The diastereomeric MHA]+ complexes with A = 1-naphthylalanine ethyl ester exhibit the largest enantioselectivity factor ever measured in the gas phase (khomo/khetero = 0.046). The origin of such an exceptional enantioselectivity is mainly attributed to the relative stability of the diastereomeric MHA]+ complexes, as demonstrated by the comparison of the kinetic results with those from collision-induced dissociation of the trimeric M2HA]+ adducts and with computational evidence. |
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