UPLC/Q-TOF MS/MS负离子模式下环氧烷型环烯醚萜苷的结构表征

利用四极杆飞行时间串联质谱(Q-TOF MS/MS)研究4个环氧烷型环烯醚萜苷同系组分(胡黄连苷Ⅰ、胡黄连苷Ⅱ、胡麻属苷、梓醇)的质谱裂解行为。在大气压化学电离源负离子(APCI~-)模式下,该类同系组分主要的裂解途径除了常见的母环上取代基的断裂,如中性丢失H_2O、CO_2和葡萄糖基等,生成~(1,6)F~-、~(1,4)F~-等特征碎片离子;另外还存在葡萄糖基环的断裂,生成~(0,4)A_1~-、~(1,4)A_1~-及~(2,4)A_1~-等碎片离子。通过对上述环氧烷型同系组分的质谱裂解行为进行归纳总结,依据其裂解规律,利用UPLC/Q-TOF MS/MS对胡黄连提取物中的环烯醚萜苷类化合物进行表征,共初步鉴定出10个环烯醚萜苷,其中包括8个环氧烷型环烯醚萜苷(胡黄连苷Ⅰ、胡黄连苷Ⅱ、胡黄连苷Ⅲ、胡黄连苷Ⅳ、黄金树苷、梓苷、婆婆纳苷和Piscroside B)和2个环戊烷型环烯醚萜(Boschnaloside和Mussaenosidic acid)。该方法有助于推动胡黄连在物质基础表征、质量控制和临床应用上的开发和利用。

Structural Characterization of Epoxytane-type Iridoid Glucosides by UPLC/Q-TOF MS/MS

Iridoid glucosides (IGs) are an important class of widely distributed secondary plant metabolites with a wide range of biological and physiological activities, which can be divided into several sub-classes, such as cyclopentene-type, cyclopentane-type, and epoxytane-type IGs. In this work, the mass spectral fragmentation behaviors of 4 standard epoxytane-type IGs, including picroside I, picroside Ⅱ, sesamoside and catalpol, were studied by negative atmospheric pressure chemical ionization (APCI^-) of quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). In the MS/MS spectra of ［M-H］^-, not only the frequently occurring neutral losses, such as H₂O, CO₂, CH₃OH and glucosidic units were detected, which confirmed the presence of functional substituents in the structures of the IGs, but also the characteristic ring cleavages of the aglycone moiety were observed, corresponding to^1,4F^-,^1,6F^- ions based on accurate mass measurements and the elemental compositions of the product ions, which could give valuable information on the basic structural skeletons. The^1,4F^- ion resulted from cleavage of the dihydropyran ring with the loss of 3-oxopropanoate, while the emerging of ^1,6F^- ions, which was different from the characteristic fragments ^2,6F^-, ^2,7F^- ions in cyclopentane-type and cyclopentene-type IGs. In addition, ring cleavages of the sugar moieties were also observed, corresponding to ^0,4A₁^-, ^1,4A₁^- and ^2,4A₁^- ions, yielding useful information for their characterization. On the other hand, the mass spectral fragmentation patterns of epoxytane-type IGs in negative ion mode were more characteristic than those in positive ion mode. And the fragmentation pathways of the IGs in APCI^- mode were found to be similar to those in ESI^- mode. Based on the fragmentation patterns of these 4 standard epoxytane-type IGs, 10 IGs were characterized in the extract of Picrohiza scrophulariiflora Pennell using ultra-performance liquid chromatography (UPLC)/Q-TOF MS/MS, of which 8 IGs were unambiguously or tentatively identified as epoxytane-type IGs (picroside Ⅰ, picroside Ⅱ, picroside Ⅲ, picroside Ⅳ, specioside, catalposide, veronicoside and piscroside B) and 2 tentatively identified as cyclopentane type IGs (boschnaloside and mussaenosidic acid). The UPLC/Q-TOF MS/MS method has been demonstrated to be an effective tool in analyzing the IG components in Picrohiza scrophulariiflora Pennell, which provide references for the studies of chemical constituents in the complex matrix and the exploitation of medicinal resources. And in the future, efforts should be made to explain the fragmentation pathways more accurately by combining the calculation of the quantum chemistry at a molecular level.