Differentiation of diastereomeric cyclic beta-amino acids by varying the neutral reagent in ion/molecule reactions studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.
Stereochemical differentiation of diasteromeric pairs of cis- and trans-2-aminocyclohexane-, -2-amino-4-cyclohexene-, and -2-aminocyclopentanecarboxylic acids was investigated with host-guest complexes where tetraethyl resorcarene was the host molecule. Diastereoselectivity was evaluated by ion/molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). The effect of varying the neutral reagent (n-propylamine, i-propylamine, diethylamine, and triethylamine) in ion/molecule reactions was evaluated. Both steric interactions and proton affinity of the neutral reagents influenced the reaction rates. High proton affinity of the neutral reagent apparently had a twofold effect. If the proton affinity of the neutral reagent was too high, the reaction tended to become too exothermic and part of the host-guest complex decomposed instead of transforming to a new host-guest complex, effecting a decrease in the reaction rate. The remaining portion of the host-guest complexes meanwhile reacted very fast with the neutral reagent due to high proton affinity causing an increase in the reaction rate. n-Propylamine and i-propylamine proved to be the best neutral reagents, providing clear diastereoselectivity for beta-amino acids in ion/molecule reactions. Interestingly, diastereoselectivity was better for flexible cyclohexane beta-amino acids (2 and 3) than for more rigid cyclopentane beta-amino acids (6 and 7). The results of ab initio and hybrid density functional theory calculations on the structures of the host-guest complexes of saturated beta-amino acids were in good agreement with the experimental results.
Hyyryläinen
Anna R M
AR
Department of Chemistry, University of Joensuu, PO Box 111, 80101 Joensuu, Finland.
Pakarinen
Jaana M H
JM
Vainiotalo
Pirjo
P
Fülöp
Ferenc
F
D000598:Amino Acids, Cyclic / Q000032:analysis* / Q000737:chemistry*; D017357:Cyclotrons; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents / Q000737:chemistry; D007477:Ions; D007536:Isomerism; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
D000598:Amino Acids, Cyclic; D007202:Indicators and Reagents; D007477:Ions