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Valnemulin, a semisynthetic pleuromutilin derivative related to tiamulin, is broadly used to treat bacterial diseases of animals. Despite its widespread use, metabolism in animals has not yet been fully investigated. To better understand valnemulin biotransformation, in this study, metabolites of valnemulinin in in vitro and in vivo rats, chickens, swines, goats, and cows were identified and elucidated using ultraperformance liquid chromatography–quadrupole/time-of-flight hybrid mass spectrometry (UPLC-Q/TOF-MS). As a result, there were totally 7 metabolites of valnemulin identified in vitro and 75, 61, and 74 metabolites detected in in vivo rats, chickens, and swines, respectively, and the majority of metabolites were reported for the first time. The main metabolic pathways of valnemulin were found to be hydroxylation in the mutilin part (the ring system) and the side chain, oxidization on the sulfur of the side chain to form S-oxides, hydrolysis of the amido bond, and acetylization in the amido of the side chain. In addition, hydroxylation in the mutilin part was proposed to be the primary metabolic route. Furthermore, the results revealed that 2β-hydroxyvalnemulin (V1) and 8α-hydroxyvalnemulin (V2) were the major metabolites for rats and swines and S-oxides (V6) in chickens.

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For detection and differentiation of two types of triterpenoid saponins based on different aglycons of the lupane and oleanane skeleton from the roots of Pulsatilla chinensis (Bunge) Regel, the silver ion was introduced and electrospray ionization multi-stage tandem mass spectrometry was applied to analyze eleven triterpenoid saponin silver complexes. The quasi-molecular ion [M+Ag](+) was observed in the full-scan MS spectra of all the silver complexes. The MS(2) data of the [M+Ag](+) ion provided structural information on the sugar sequence of the oligosaccharide chains and the aglycon of the saponins. There are two patterns in the cleavage pathway of oleanane-type saponins. One is elimination of the sugar chain and subsequent loss of the carboxylic group which is the same as the cleavage of lupine-type saponins. The other is loss of the distinguishing ions at m/z 72 and 28 (C(2)H(4)) followed by loss of the carboxylic group. Diagnostic fragmentation pathways of the silver complexes of the saponins allow successful identification of the two types of saponins from the roots of Pulsatilla chinensis (Bunge) Regel.