Characterization and Identification of the Ent-Kaurane Diterpenoids in Isodonis Excisoidis Herba Using UHPLC-LTQ-Orbitrap-MS

Isodonis Excisoidis Herba (IEH) is a newly discovered herbal medicine used to treat esophageal cancer, chronic pharyngitis, and hepatitis, and ent-kaurane diterpenoids are its main active components. However, systematic studies on the chemical profile of ent-kaurane diterpenoids are lacking. In this study, UHPLC-LTQ-Orbitrap-MS was performed to investigate the fragmentation behaviors of three different types of ent-kaurane diterpenoids from IEH. Bridgehead-unsubstituted 7,20-epoxy-ent-kaurane diterpenoids yielded ions with typical losses of R₇H, R₁H, R₁₄H, CH₂O, CO, and R₆H. The [M + NH₄ - NH₃ - R₂₀]⁺ precursor ions at 331.1895 and the characteristic ions at <i>m</i>/<i>z</i> 313.1792, 295.1686, 285.1842, 277.1581, 267.1737, and 249.1632 were the most possible fragmentation pathways for bridgehead-substituted 7,20-epoxy-ent-kaurane diterpenoids. Fragmentation with the successive loss of multiple 18, 42, or 60 Da occurring in the OH groups and OAc groups is characteristic of 7,20-non-epoxy-kaurane diterpenoids. Using accurate mass measurements for each precursor ion and the subsequent fragmented ions, a total of 94 ent-kaurane diterpenoids were identified or tentatively characterized in IEH, including 48 potentially new ent-kaurane diterpenoids.