Diastereoselective Fragmentation of Chiral alfa-Aminophosphonic Acids/Metal Ion aggregates

Diastereomeric clusters of general formula [MAB2]+ and [MA2B]+ (M = Li.I/, Na(I), Ag(I), Ni(II)-H, or Cu(II)-H; A = .R/-(-)- and (S)-(+)-(1-aminopropyl)phosphonic acid; B = .1R)-(-)- and (1S)-(+)-(1-aminohexyl)phosphonic acid) have been readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissociation (CID) investigated. CID of diastereomeric complexes, e.g. [MAS(BS)2]+ and [MAR(BS/2]+, leads to fragmentation patterns characterized by Rhomo = [MASBS]+/[M(BS)2]+ and Rhetero = [MARBS]+/[M(BS/2]+ abundance ratios, which depend upon the relative stability of the diastereomeric [MASBS]+ and [MARBS]+ complexes in the gas phase. The chiral resolution factor Rchiral = Rhomo/Rhetero is found to depend not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB2]+ or [MA2B]+.