Xia Yong-Gang, Liang Jun, Li Guo-Yu, Yang Bing-You, Kuang Hai-Xue
Key Laboratory of Chinese Materia Medica (Heilongjiang University of Chinese Medicine), Ministry of Education, Harbin 150040, PR China.
Pharmaceutical College, Harbin Medical University, Harbin 150086, PR China.
J Pharm Biomed Anal. 2015 Aug 10;112:106-15. doi: 10.1016/j.jpba.2015.04.024. Epub 2015 Apr 24.
The saponins in Caulophyllum robustum have not yet been fully characterized. Furthermore these saponins are often present in trace amounts and are structurally complex. Here, a simple direct infusion electrospray ion trap multiple-stage tandem mass spectrometry (DI-ESI-IT-MS(n)) method was described for the characterization of trace C. robustum saponins. Eight reference saponins from the C. robustum hairy root were investigated by DI-ESI-IT-MS(n) in positive ion mode. Some fragmentation approaches were proposed through analysis of the M+Na ions: (1) preferential cleavage of the C-28 ester glycosidic bond to provide complementary Y0α+Na and Bα+Na ions for bidesmosidic saponins; (2) diagnostically neutral loss of CO2 from free carboxyl groups at C-28 for monodesmosidic saponins; and (3) the ion intensity ratio between C2β+Na and B2β+Na, which is sensitive to the structural differences between the two isomeric β-sugar chains (Glc → (2)Ara and Glc → (3)Ara). The DI-ESI-IT-MS(n) method was successfully used for the analysis of trace C. robustum saponins with M+Na ions at m/z 1745.6, 1729.5, 1583.7, 1567.7, 1421.7 and 1405.7. This article highlights the discovery and identification of complex α- and β-oligosaccharide moieties in Caulophyllum saponins by glycosidic product ions along with cross ring cleavage product ions. Five oligosaccharide moieties were unambiguously or tentatively identified as Rha → (4)Glc → (6)Glc → (4)Rha → (4)Glc → (6)Glc, Glc → (4)Glc → (6)Glc → (4)Rha → (4)Glc → (6)Glc, Rha → Glc → Glc (Glc) → (2,3)Ara, Glc → Glc (Glc) → (2,3)Ara and Glc (Glc) → (2,3)Ara. Accuracy of the analytical procedure was demonstrated by structural identification of two saponins isolated using 1D and 2D-NMR spectroscopy. The DI-ESI-IT-MS(n) method facilitates rapid discovery and analysis of trace Caulophyllum saponins and is a powerful and practical tool for structural characterization of complex oligosaccharide moieties in triterpene saponins.
粗壮红毛七中的皂苷尚未得到充分表征。此外，这些皂苷通常含量微量且结构复杂。在此，描述了一种简单的直接进样电喷雾离子阱多级串联质谱法（DI-ESI-IT-MS(n)）用于表征微量的粗壮红毛七皂苷。采用DI-ESI-IT-MS(n)在正离子模式下研究了粗壮红毛七毛状根中的8种参考皂苷。通过对M+Na离子的分析提出了一些裂解方法：(1) C-28酯糖苷键优先裂解，为双糖链皂苷提供互补的Y0α+Na和Bα+Na离子；(2) 单糖链皂苷在C-28处的游离羧基发生诊断性的CO2中性丢失；(3) C2β+Na与B2β+Na之间的离子强度比，其对两种异构β-糖链（Glc→(2)Ara和Glc→(3)Ara）之间的结构差异敏感。DI-ESI-IT-MS(n)方法成功用于分析m/z为1745.6、1729.5、1583.7、1567.7、1421.7和1405.7的微量粗壮红毛七皂苷的M+Na离子。本文通过糖苷产物离子以及跨环裂解产物离子突出了在红毛七皂苷中复杂α-和β-寡糖部分的发现与鉴定。明确或初步鉴定了5种寡糖部分，分别为Rha→(4)Glc→(6)Glc→(4)Rha→(4)Glc→(6)Glc、Glc→(4)Glc→(6)Glc→(4)Rha→(4)Glc→(6)Glc、Rha→Glc→Glc(Glc)→(2,3)Ara、Glc→Glc(Glc)→(2,3)Ara和Glc(Glc)→(2,3)Ara。通过对使用一维和二维核磁共振光谱分离得到的两种皂苷进行结构鉴定，证明了分析方法的准确性。DI-ESI-IT-MS(n)方法有助于快速发现和分析微量的红毛七皂苷，是用于三萜皂苷中复杂寡糖部分结构表征的一种强大而实用的工具。
