Analysis of cipadesin limonoids from Cipadessa cinerascens using electrospray ionization quadrupole time-of-flight tandem mass spectrometry and quantum chemical calculations

Rationale: Limonoids, a class of tetranortriterpenoids, exhibit various biological effects, such as insect antifeedant and growth regulating activities, antimicrobial activity, potent cell adhesion inhibitory effects, antimalarial activity, anticancer activities, and antioxidant activity. The potential application brings the need for reliable, fast and low-cost analysis of this class of compounds.

Methods: Six cipadesin limonoids (1-6), including a pairs of isomers, from leaves and barks of Cipadessa cinerascens were investigated by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in positive-ion mode. Characteristic processes were further studied by theoretical calculations.

Results: 1,3-Hydrogen rearrangement might play a significant role in the cleavage of -O- bridge bond in ring B and further produces some characteristic ions. For [M + Na](+) precursor ions, the product ion at m/z 133 might indicate the structure of ring A and the losses of CO(2) and AcOH occur readily. Interestingly, the radical product ion at m/z 460 from [M + Na](+) ions seems to be the characteristic ion for compound 1. A deuterium-labeling experiment supported the processes forming the radical ion. For [M + NH(4)](+) ions, high-abundance product ions resulting from sequential loss of AcOH can be observed. In addition, a pairs of isomers was unambiguously differentiated based on MS or MS/MS spectra.

Conclusions: In summary, sufficient information obtained from fragmentation experiments of [M + Na](+), [M + NH(4)](+) or [M + H](+) precursor ions is especially valuable for rapid identification of these limonoids or their metabolites in complex mixtures. The high-abundance radical product ion is of scientific interest.