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

Diastereomeric clusters [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) were readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissocn. (CID) studied. 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 resoln. factor Rchiral = Rhomo/Rhetero depends not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB2]+ or [MA2B]+. The origin of this behavior is discussed.