Exceptional gas-phase enantioselectivity of chiral tetramide macrocycles.
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.
Filippi
Antonello
A
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive. Università La Sapienza, 00185 Roma, Italy.
Gasparrini
Francesco
F
Pierini
Marco
M
Speranza
Maurizio
M
Villani
Claudio
C