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 MSⁿ (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.