Structural Characterization of Quinolizidine Alkaloids in Heimia salicifolia by Electrospray Ionization Tandem Mass Spectrometry

Heimia salicifolia (Lythraceae), also known as sun opener or shrubby yellow crest, is a wild flowering shrub distributed from Mexico, southwestern Texas to northern Argentina. It has been used as antipyretic, emetic, laxative, diuretic and anti-inflammatory and for its wound healing activity in Central and South America. The folkloric reports claimed the plant had psychotomimetic activity [1]. Nine quinolizidine alkaloids and biphenyl quinolizidine lactone alkaloids isolated from H. salicifolia have been structurally characterized by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MSⁿ) coupled with an ion-trap analyzer. The fragmentation patterns of these alkaloids are dominated by the existence of bridge between C-2 and C-4, and less affected in accordance with structural variations of substitution at C-2 and C-12. When forming the lactone bridge between C-2 and C-4 over a biphenyl moiety, a neutral loss of 44 Da corresponding to carbon dioxide is easily generated. Moreover, the product ions will further yield fragment ions related to the cleavage of A-ring at C-1/C-2 and C-4/C-5. B ring bearing nitrogen atom has been found as one very easily loss group in the fragmentation pathways of all analyzed quinolizidine alkaloids. The results of this study can benefit the determination of trace quinolizidine alkaloids and biphenyl quinolizidine lactone alkaloids in crude plant extract and also provide background information to aid the structural investigations of related biological studies and forensic science. Acknowledgements: This research is funded in part by “Science Based Authentication of Dietary Supplements” Funded by the Food and Drug Administration grant number 2 U01 FD 002071-07. References: [1] Malone MH, et al. (1994), J Ethnopharm, 42: 135–159.

Fig. 1 Fragmentation pattern proposed for [M+H]⁺ ions of vertine.