Negative ion fast atom bombardment-tandem mass spectrometry for structural analysis of isoprenoid diphosphates

Abstract Applicability of negative ion fast atom bombardment (FAB)-tandem mass spectrometry ( MS MS ) was examined in trace mixture analyses and structural assignments of some isoprenoid diphosphates. Negative ion FAB-MS spectra using a glycerol matrix of these isoprenoid diphosphates showed predominantly molecular ions (M-H) − together with fragment ions at m z 177 (H 3 P 2 O 7 ) − , 176 (H 2 P 2 O 7 ) − , 159 (HP 2 O 6 ) − , and 79 (PO 3 ) − which were characteristic of the diphosphate ester moiety. The molecular ions did not overlap with peaks arising from any impurities even when crude sample such as butanol extracts from enzymatic reaction mixtures were directly analyzed without any purification. Moreover, collisionally activated dissociation spectra of the molecular ion showed many structurally significant fragment ions which enabled us to elucidate the structures of such irregular alkyl chain moieties as those having a homoisoprenoid skeleton or substituted structures. These studies indicate that negative ion FAB-MS MS is a simple and useful technique for trace mixture analysis and structure elucidation of isoprenoid diphosphates.