Main iridoid glycosides and HPLC/DAD-Q-TOF-MS/MS profile of glycosides from the antioxidant extract of Eucommia ulmoides Oliver seeds

Abstract

Eucommia ulmoides Oliver, a commercial tree widely in China, has long been used in traditional Chinese medicine, yet few phytochemical investigations on the seeds have been reported. The aim of the present research is to systematically isolate and identify glycosides from the antioxidant extract of E. ulmoides seeds. Antioxidant activity of each extract was evaluated by DPPH and ABTS methods based on free radical scavenging. DPPH and ABTS tests showed that the ethanol extract and each extractive fraction had strong antioxidant effects, of which ethyl acetate and n-butanol fraction showed more significant antioxidant activities with IC50 values at 87.14±0.08, 66.30±0.06μg/mL by DPPH assay and 139.61±0.05, 231.35±1.03μg/mL by ABTS test respectively. Four main iridoid glycosides were isolated firstly and structurally determined by NMR and mass spectrum data and their antioxidant effects were measured. Then other minor compounds in antioxidant extract were identified by HPLC/DAD-Q-TOF-MS/MS, totally nineteen compounds were tentatively identified by their chromatographic behaviors and mass spectral characteristics, which included ten iridoid glycosides, seven flavonoid glycosides and two chlorogenic acid isomers. Three iridoid glycoside polymers (14, 15 and 18) were tentatively identified as new compounds and compounds 5, 9 and 12 were reported in the E. ulmoides seeds for the first time. Thus, the extract and iridoid glycosides of E. ulmoides seeds had strong antioxidant effects and also had the potential commercialization for pharmaceutical and nutraceutical purposes.