Structural determination of synthetic monoacetyldiglycerides by tandem mass spectrometry of sodium-adducted molecules

A variety of synthetic monoacetyldiglycerides (MADGs), which show hematopoietic stem cell stimulating activity, were investigated using high-energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS) coupled with fast-atom bombardment (FAB). CID of sodium-adducted molecules, [M + Na]+, generated product ions highly informative on their structure. In particular, two type of ions (named E2,3 and J) and the relative intensity ratio (G2/G1) of two product ions (named G1 and G2) by the loss of free fatty acids (-Rn′ COOH) provided definitive information about the position of two long-chain acyl groups on the glycerol backbone. In addition, charge-remote fragmentation (CRF) along the long hydrocarbon chains of two fatty acyl groups determined the position of each double bond. Thus, this direct and rapid method can be applied to the structural determination of individual molecular species in a mixture of MADGs isolated from biological origins.