Identification of C‐glycosyl flavones and O‐glycosyl flavones in five Dendrobium species by high‐performance liquid chromatography coupled with electrospray ionization multi‐stage tandem MS

Abstract

Flavones are widely used in traditional Chinese medicine (TCM) and are the pharmacologically active ingredients of many medicinal plants, such as Dendrobium. With the increasing demand for medicinal Dendrobium, the identification of characteristic flavones that can serve as chemical markers for quality control is critical step for quality assurance and safety in the TCM industry. Methods: High-performance liquid chromatography coupled with electrospray ionization multi-stage tandem mass spectrometry (HPLC/ESI-MS n ) was used to identify the chemical constituents in five types of Dendrobium: D. crystallinum, D. falconeri, D. strongylanthum, D. moniliforme, and D. gratiosissimum. Results: A total of seventy-six C-glycosyl flavones and three O-glycosyl flavones were identified, of which fifteen C-glycosyl flavones were found in D. crystallinum, twenty four were found in D. falconeri, thirty were found in D. strongylanthum, seven were found in D. moniliforme (also called "Huangtongpi", from Anhui, China), fifteen were found in D. moniliforme (also called "Zitongpi", from Yunnan, China) and seventeen were found in D. gratiosissimum. Additionally, three flavone O-glycosides were all found in D. strongylanthum. Conclusions: The results of this study may be useful for the quality assessment and for the application of D. crystallinum, D. falconeri, D. strongylanthum, D. moniliforme, and D. gratiosissimum. This study provides comprehensive information for identification of flavones from other Chinese herbs. | INTRODUCTIONDendrobium, also known as "Shihu", belongs to the orchid family. 1,2 Although seventy-four species and two varieties are known, only about forty species have medicinal value. Furthermore, some of these species with high medicinal values are now endangered. 3 Fortunately, artificial planting of Dendrobium species has been a great success in China. Some Dendrobium species have been used in traditional Chinese medicine (TCM) for centuries. At present, it is demonstrated that Dendrobium has comprehensive bioactivities, involving antioxidant, anti-cancer, anti-inflammatory and immunomodulatory. 4 According to the Chinese Pharmacopoeia (2020 version), several Dendrobium species such as, D. nobile, D. huoshanense, D. chrysotoxum, D. fimbriatum and similar species are all used as "Shihu". Nowadays, Dendrobium is not only used as medicine, but is also used as food and a tonic to condition the body. 5 Because many Dendrobium species have similar appearance and the species are more difficult to identify after processing, the market is flooded with inexpensive Dendrobium that is used as a counterfeit for precious Dendrobium. To prevent counterfeiting, it is necessary to establish an accurate and efficient identification method, such as fingerprinting method based on chromatographic techniques. The

Identification of three types of O‐glycosylated flavonoids in Dendrobium loddigesii, Dendrobium primulinum, Dendrobium crepidatum, Dendrobium porphyrochilum, and Dendrobium hancockii using mass spectrometry

“…According to our previous research, most of the flavonoid glycosides in Dendrobium are C ‐glycosylated flavones, and their acylated derivatives in some Dendrobium varieties also have certain characteristics. The flavonoid aglycones mainly included apigenin [Ag = 270], luteolin [Ag = 286], and chrysoeriol [Ag = 300] 10–15 . In this study, C ‐glycosylated flavones were also found in D. hancockii , but the main constituent was O ‐glycosylated flavones, among which 5,7‐dihydroxyflavone [Ag = 254] has rarely been reported in other species.…”

“…For example, C ‐glycosyl flavones have been shown to lose 120 and 90 Da, corresponding to hexose substituents; 90 and 60 Da corresponding to pentose substituents; and 104 and 74 Da, corresponding to methyl pentose substituents 17 . Furthermore, the intensity of − 0,2 X is greater than that of − 0,3 X. Glucose, arabinose, xylose, and rhamnose moieties are the most common glycosyls in the flavonoids of Dendrobium 10–15 . The method of determining the substituted forms of C ‐glycosylated flavones allows the identification of the flavonoid glycosides as 6/8 mono‐ C ‐glycosyl flavones of the corresponding aglycone, when characteristic ion peaks of [Ag + 41] − , [Ag + 71] − , [Ag + 41–18] − , and [Ag + 71–18] − fragments appear in the mass spectrum, or as 6,8‐di‐ C ‐glycosyl flavones of the corresponding aglycone, when characteristic fragment ion peaks of [Ag + 83] − , [Ag + 113] − , [Ag + 83–18] − , and [Ag + 113–18] − are observed 29,30 (Ag: aglycone molecular mass).…”

“…In recent years, research has shown that C-glycosylated flavones and their acylated derivatives in different species of Dendrobium or the same species but from different production areas play a crucial role in the identification process. [10][11][12][13][14][15] A few O-glycosylated flavonols have also proven to be characteristic; for example, rutin has important identification significance in Dendrobium officinale, 10,14,15 and naringin, as a dihydroflavone aglycone, has been detected in varieties of Dendrobium 16 ; however, its specificity was poor, and its glycosides are rarely studied. From an analytical point of view, qualitative profiling of flavonoids in plant extracts is a complex task, as "flavonoids" comprise a huge group of structurally diverse analytes formed by a variety of core compounds (aglycones) that mostly occur in plant material in the form of complex derivatives.…”

“…They are richly found in Dendrobium . In recent years, research has shown that C ‐glycosylated flavones and their acylated derivatives in different species of Dendrobium or the same species but from different production areas play a crucial role in the identification process 10–15 . A few O ‐glycosylated flavonols have also proven to be characteristic; for example, rutin has important identification significance in Dendrobium officinale , 10,14,15 and naringin , as a dihydroflavone aglycone, has been detected in varieties of Dendrobium 16 ; however, its specificity was poor, and its glycosides are rarely studied.…”

Comparative metabolite analysis of Piper sarmentosum organs approached by LC–MS-based metabolic profiling

“…They serve as antioxidants, UV-protectants and play a pivotal role as coloring components of flowering plants [ 100 ]. MS/MS analysis can provide structural information about flavonoids including the structure of aglycones, glycosylation patterns and the presence of other substituents such as 3-hydroxy-3-methylglutaryl and other acyl residues [ 101 ]. According to previous studies of P. sarmentosum , the major identified flavonoid aglycone was apigenin (aglycon m/z 271) [ 102 ].…”