Fragmentation Behavior for Iridoid Glucosides and Anthraquinones in Morinda officinalis by ESI-Q-TOF MS/MS in Negative Ion Mode

Morinda officinalis, the dried root of Morinda officinalis How, is commonly used as a traditional Chinese medicine for the treatment of impotence and osteo-porosis in clinical theraphy, and this effect is supposed to be attributed to iridoid glycoside and anthraquinone compounds. Recent years, liquid chromatography coupled with high resolution mass spectrometry was widely used for the identification of components from traditional Chinese medicine based on the fragmentation pathways of main components. However, reports on the fragmentation pathway of main ingredients in M. officinalis were limited. Therefore, in this paper, the fragmentation pathways of 4 iridoid glycosides (monotropein, deacetyla sperulosidic acid, asperulosidic acid and asperuloside) and 2 anthraquinones (rubiadin-1-methyl ether and rubiadin) in M. officinalis were investigated using electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-Q-TOF MS/MS) in negative ion mode. The deprotonated M-H^- were observed by ESI-MS, from which the molecular weights were deduced. The collision induced dissociation (CID) data of M-H^- ions provided fragmentation information of the compounds of interest. The main and typical fragmentation pathway of iridoid glycosides were neutral losses of H₂O, CO₂, CH₃COOH and glucosidic units. Meanwhile, the cleavages of dihydropyranoid and sugar ring were also observed. The common fragment ions of m/z 113, 101 were the characteristic ions for the cleavages of dihydropyranoid. The fragmentation process of anthraquinones was continual loss of CO followed by dissociation of CO₂. The experimental results indicated that the fragmentation behavior of iridoid glycosides and anthraquinones was reasonable and could provide the basis for their structures elucidation and identification.