Characterization of diterpenoids in the bark of Pseudolarix kaempferi by HPLC-ESI/MSn

Fragmentation behavior of diterpenoids was investigated by ESI/MSn and the qualitative analysis of diterpenoids in the bark of Pseudolarix kaempferi was performed using high-performance liquid chromatography/ multi-stage mass spectrometry (HPLC-ESI/MSn). The characteristic fragmentation behaviors of the diterpenoids are the cleavages of the lactone ring and C4-O bond. Furthermore, the eliminations of substituent groups at C-18, C-7 and C-8 can also be observed in the MS" (n = 3-4) spectra. For C-4 acetoxy subsititued diterpenoids, [M+Na-60]+ and [M-H-104] are the base peaks of MS2 spectra in the positive and negative ionization modes, respectively. For C-4 hydroxyl subsititued diterpenoids, [M+Na-44]+ and [M-H-62] are the base peaks of MS2 in the positive and negative ionization modes, respectively. For C-18 glucosylated or esterized diterpenoids, [M+Na-44]+ is the base peak of MS2 spectra in positive ionization mode. These fragmentation rules were successfully exploited in the identification of diterpenoids in methanol/water (6:4) extract of P. kaempferi by LC-MS in positive ionization mode. A total of 9 diterpenoids were identified or tentatively characterized, and one of them is reported here for the first time. The described method could be utilized for the sensitive and rapid qualitative analysis of P. kaempferi.