Iridoid glycosides have various biological activities, including antioxidant, anti-inflammatory, anti-tumor, hepatoprotective, antitussive, and as analgesic agents. Their potential applications require rapid, sensitive analytical methods for their detection and distinction.

However, some iridoid glycosides, especial dimers, are difficult to identify. Mass spectrometry (MS) is a widely applied method for the identification of trace natural products because it is rapid, sensitive, and consumes small amounts of sample.

Studies of iridoid glucosides using electrospray ionization (ESI)-MS have been reported. However, few have addressed the fragmentation of iridoid glucoside dimers, especially, isomeric dimers were studied.

The CID-fragmentation analysis of the three isomeric iridoid glucoside dimers was performed with ESI-QTOF-MS/MS/MS in the positive-ion mode. The MS/MS spectra of the three isomers are clearly different. Notably, both of the characteristic product ions, at m/z 469 and 487, in the MS/MS spectra of [M + Na]+ for saprosmoside E and saprosmoside D, respectively, have two possible structures.

The exact structures can be confirmed by comparing the MS/MS/MS spectra and MS/MS spectra of [M + Na]+ for paederoside and paederosidic acid, respectively. In summary, the characteristic product ions from these three isomers are especially valuable for their rapid identification of these isomers or the identification of their metabolites in complex matrices. The structural identification of isomeric ions is of interest.

Researchers from Chongqing University and Chengdu Institute of Biology cooperated to study this job.