Identification of Oxygenated Fatty Acid as a Side Chain of Lipo-Alkaloids in Aconitum carmichaelii by UHPLC-Q-TOF-MS and a Database.

Ying Liang,Liang Liu,Hua Zhou,Jian-Lin Wu,Zhongqiu Liu,Guanyu Yan,Na Li,Ying Liu,Elaine Leung

doi:10.3390/molecules21040437

Abstract

Lipo-alkaloid is a kind of C19-norditerpenoid alkaloid usually found in Aconitum species. Structurally, they contain an aconitane skeleton and one or two fatty acid moieties of 3–25 carbon chains with 1–6 unsaturated degrees. Analysis of the lipo-alkaloids in roots of Aconitum carmichaelii resulted in the isolation of six known pure lipo-alkaloids (A1–A6) and a lipo-alkaloid mixture (A7). The mixture shared the same aconitane skeleton of 14-benzoylmesaconine, but their side chains were determined to be 9-hydroxy-octadecadienoic acid, 13-hydroxy-octadecadienoic acid and 10-hydroxy-octadecadienoic acid, respectively, by MS/MS analysis after alkaline hydrolysis. To our knowledge, this is the first time of the reporting of the oxygenated fatty acids as the side chains in naturally-occurring lipo-alkaloids. In order to identify more lipo-alkaloids, a compound database was established based on various combinations between the aconitane skeleton and the fatty acid chain, and then, the identification of lipo-alkaloids was conducted using the database, UHPLC-Q-TOF-MS and MS/MS. Finally, 148 lipo-alkaloids were identified from A. carmichaelii after intensive MS/MS analysis, including 93 potential new compounds and 38 compounds with oxygenated fatty acid moieties.

Highlights

IntroductionLipo-alkaloid is a kind of C19-norditerpenoid alkaloid usually found in Aconitum species
Lipo-alkaloid is a kind of C19-norditerpenoid alkaloid usually found in Aconitum species.Structurally, they consist of an aconitane skeleton and one or two fatty acid moieties of 3–25 carbon chains with 1–6 unsaturated degrees [1]
We reported 13 aconitane skeletons in the lipo-alkaloids with their main fragmentation ions from the neutral losses of MeOH, H2O, CO and BzOH (Figure 6 and Table 1)

Summary

Introduction

Lipo-alkaloid is a kind of C19-norditerpenoid alkaloid usually found in Aconitum species. They consist of an aconitane skeleton and one or two fatty acid moieties of 3–25 carbon chains with 1–6 unsaturated degrees [1]. Because naturally-occurring lipo-alkaloids are so close structurally, it is very difficult to purify them from the mixture. Their characterization is mainly conducted by high sensitive mass spectrometry (MS) or liquid. Only one pure lipo-alkaloid, 8-O-azeloyl-14-benzoylaconine, was isolated and elucidated by NMR from plants [12]. The separation of naturally-occurring lipo-alkaloids was optimized using column chromatography (CC), and six pure lipo-alkaloids (A1–A6) were obtained from a natural source for the first time

Methods

Results

Conclusion