Diastereochemical Differentiation of β-Amino Acids Using Host–Guest Complexes Studied by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Host–guest complexes where tetraethyl resorcarene was the host molecule were used to study the stereoselectivity of diasteromeric pairs of di-endo- and di-exo-2,3-disubstituted norbornane and norbornene amino acids by ion–molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Both methods showed stereoselectivity for the diastereomeric pairs. Particularly high selectivity was achieved for di-endo- and di-exo-2,3-disubstituted norbornane amino acids with ion–molecule reactions. Also, ab initio and hybrid density functional theory calculations were performed to study the different structures of the host–guest complexes. Hydrogen bonding was crucial for the calculated lowest energy structures, and sterical considerations satisfactorily explained the ion–molecule reaction results.